diff --git a/.gitattributes b/.gitattributes
index 84c7add0..14c3c359 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,4 +1,3 @@
 /Tests export-ignore
 /phpunit.xml.dist export-ignore
-/.gitattributes export-ignore
-/.gitignore export-ignore
+/.git* export-ignore
diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
new file mode 100644
index 00000000..4689c4da
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -0,0 +1,8 @@
+Please do not submit any Pull Requests here. They will be closed.
+---
+
+Please submit your PR here instead:
+https://github.com/symfony/symfony
+
+This repository is what we call a "subtree split": a read-only subset of that main repository.
+We're looking forward to your PR there!
diff --git a/.github/workflows/close-pull-request.yml b/.github/workflows/close-pull-request.yml
new file mode 100644
index 00000000..e55b4781
--- /dev/null
+++ b/.github/workflows/close-pull-request.yml
@@ -0,0 +1,20 @@
+name: Close Pull Request
+
+on:
+  pull_request_target:
+    types: [opened]
+
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: superbrothers/close-pull-request@v3
+      with:
+        comment: |
+          Thanks for your Pull Request! We love contributions.
+
+          However, you should instead open your PR on the main repository:
+          https://github.com/symfony/symfony
+
+          This repository is what we call a "subtree split": a read-only subset of that main repository.
+          We're looking forward to your PR there!
diff --git a/ExecutableFinder.php b/ExecutableFinder.php
index feee4ad4..89edd22f 100644
--- a/ExecutableFinder.php
+++ b/ExecutableFinder.php
@@ -19,7 +19,15 @@
  */
 class ExecutableFinder
 {
-    private $suffixes = ['.exe', '.bat', '.cmd', '.com'];
+    private const CMD_BUILTINS = [
+        'assoc', 'break', 'call', 'cd', 'chdir', 'cls', 'color', 'copy', 'date',
+        'del', 'dir', 'echo', 'endlocal', 'erase', 'exit', 'for', 'ftype', 'goto',
+        'help', 'if', 'label', 'md', 'mkdir', 'mklink', 'move', 'path', 'pause',
+        'popd', 'prompt', 'pushd', 'rd', 'rem', 'ren', 'rename', 'rmdir', 'set',
+        'setlocal', 'shift', 'start', 'time', 'title', 'type', 'ver', 'vol',
+    ];
+
+    private $suffixes = [];
 
     /**
      * Replaces default suffixes of executable.
@@ -44,43 +52,52 @@ public function addSuffix(string $suffix)
      * @param string|null $default   The default to return if no executable is found
      * @param array       $extraDirs Additional dirs to check into
      *
-     * @return string|null The executable path or default value
+     * @return string|null
      */
-    public function find(string $name, string $default = null, array $extraDirs = [])
+    public function find(string $name, ?string $default = null, array $extraDirs = [])
     {
-        if (ini_get('open_basedir')) {
-            $searchPath = array_merge(explode(\PATH_SEPARATOR, ini_get('open_basedir')), $extraDirs);
-            $dirs = [];
-            foreach ($searchPath as $path) {
-                // Silencing against https://bugs.php.net/69240
-                if (@is_dir($path)) {
-                    $dirs[] = $path;
-                } else {
-                    if (basename($path) == $name && @is_executable($path)) {
-                        return $path;
-                    }
-                }
-            }
-        } else {
-            $dirs = array_merge(
-                explode(\PATH_SEPARATOR, getenv('PATH') ?: getenv('Path')),
-                $extraDirs
-            );
+        // windows built-in commands that are present in cmd.exe should not be resolved using PATH as they do not exist as exes
+        if ('\\' === \DIRECTORY_SEPARATOR && \in_array(strtolower($name), self::CMD_BUILTINS, true)) {
+            return $name;
         }
 
-        $suffixes = [''];
+        $dirs = array_merge(
+            explode(\PATH_SEPARATOR, getenv('PATH') ?: getenv('Path')),
+            $extraDirs
+        );
+
+        $suffixes = [];
         if ('\\' === \DIRECTORY_SEPARATOR) {
             $pathExt = getenv('PATHEXT');
-            $suffixes = array_merge($pathExt ? explode(\PATH_SEPARATOR, $pathExt) : $this->suffixes, $suffixes);
+            $suffixes = $this->suffixes;
+            $suffixes = array_merge($suffixes, $pathExt ? explode(\PATH_SEPARATOR, $pathExt) : ['.exe', '.bat', '.cmd', '.com']);
         }
+        $suffixes = '' !== pathinfo($name, PATHINFO_EXTENSION) ? array_merge([''], $suffixes) : array_merge($suffixes, ['']);
         foreach ($suffixes as $suffix) {
             foreach ($dirs as $dir) {
+                if ('' === $dir) {
+                    $dir = '.';
+                }
                 if (@is_file($file = $dir.\DIRECTORY_SEPARATOR.$name.$suffix) && ('\\' === \DIRECTORY_SEPARATOR || @is_executable($file))) {
                     return $file;
                 }
+
+                if (!@is_dir($dir) && basename($dir) === $name.$suffix && @is_executable($dir)) {
+                    return $dir;
+                }
             }
         }
 
+        if ('\\' === \DIRECTORY_SEPARATOR || !\function_exists('exec') || \strlen($name) !== strcspn($name, '/'.\DIRECTORY_SEPARATOR)) {
+            return $default;
+        }
+
+        $execResult = exec('command -v -- '.escapeshellarg($name));
+
+        if (($executablePath = substr($execResult, 0, strpos($execResult, \PHP_EOL) ?: null)) && @is_executable($executablePath)) {
+            return $executablePath;
+        }
+
         return $default;
     }
 }
diff --git a/InputStream.php b/InputStream.php
index 4f8f7133..0c45b524 100644
--- a/InputStream.php
+++ b/InputStream.php
@@ -17,6 +17,8 @@
  * Provides a way to continuously write to the input of a Process until the InputStream is closed.
  *
  * @author Nicolas Grekas <p@tchwork.com>
+ *
+ * @implements \IteratorAggregate<int, string>
  */
 class InputStream implements \IteratorAggregate
 {
@@ -28,7 +30,7 @@ class InputStream implements \IteratorAggregate
     /**
      * Sets a callback that is called when the write buffer becomes empty.
      */
-    public function onEmpty(callable $onEmpty = null)
+    public function onEmpty(?callable $onEmpty = null)
     {
         $this->onEmpty = $onEmpty;
     }
@@ -67,7 +69,7 @@ public function isClosed()
     }
 
     /**
-     * @return \Traversable
+     * @return \Traversable<int, string>
      */
     #[\ReturnTypeWillChange]
     public function getIterator()
diff --git a/LICENSE b/LICENSE
index 9ff2d0d6..0138f8f0 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2004-2021 Fabien Potencier
+Copyright (c) 2004-present Fabien Potencier
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/PhpExecutableFinder.php b/PhpExecutableFinder.php
index e4f03f76..c3a9680d 100644
--- a/PhpExecutableFinder.php
+++ b/PhpExecutableFinder.php
@@ -29,20 +29,17 @@ public function __construct()
     /**
      * Finds The PHP executable.
      *
-     * @return string|false The PHP executable path or false if it cannot be found
+     * @return string|false
      */
     public function find(bool $includeArgs = true)
     {
         if ($php = getenv('PHP_BINARY')) {
-            if (!is_executable($php)) {
-                $command = '\\' === \DIRECTORY_SEPARATOR ? 'where' : 'command -v';
-                if ($php = strtok(exec($command.' '.escapeshellarg($php)), \PHP_EOL)) {
-                    if (!is_executable($php)) {
-                        return false;
-                    }
-                } else {
-                    return false;
-                }
+            if (!is_executable($php) && !$php = $this->executableFinder->find($php)) {
+                return false;
+            }
+
+            if (@is_dir($php)) {
+                return false;
             }
 
             return $php;
@@ -52,12 +49,12 @@ public function find(bool $includeArgs = true)
         $args = $includeArgs && $args ? ' '.implode(' ', $args) : '';
 
         // PHP_BINARY return the current sapi executable
-        if (\PHP_BINARY && \in_array(\PHP_SAPI, ['cgi-fcgi', 'cli', 'cli-server', 'phpdbg'], true)) {
+        if (\PHP_BINARY && \in_array(\PHP_SAPI, ['cli', 'cli-server', 'phpdbg'], true)) {
             return \PHP_BINARY.$args;
         }
 
         if ($php = getenv('PHP_PATH')) {
-            if (!@is_executable($php)) {
+            if (!@is_executable($php) || @is_dir($php)) {
                 return false;
             }
 
@@ -65,12 +62,12 @@ public function find(bool $includeArgs = true)
         }
 
         if ($php = getenv('PHP_PEAR_PHP_BIN')) {
-            if (@is_executable($php)) {
+            if (@is_executable($php) && !@is_dir($php)) {
                 return $php;
             }
         }
 
-        if (@is_executable($php = \PHP_BINDIR.('\\' === \DIRECTORY_SEPARATOR ? '\\php.exe' : '/php'))) {
+        if (@is_executable($php = \PHP_BINDIR.('\\' === \DIRECTORY_SEPARATOR ? '\\php.exe' : '/php')) && !@is_dir($php)) {
             return $php;
         }
 
@@ -85,7 +82,7 @@ public function find(bool $includeArgs = true)
     /**
      * Finds the PHP executable arguments.
      *
-     * @return array The PHP executable arguments
+     * @return array
      */
     public function findArguments()
     {
diff --git a/PhpProcess.php b/PhpProcess.php
index 2bc338e5..3a1d147c 100644
--- a/PhpProcess.php
+++ b/PhpProcess.php
@@ -32,7 +32,7 @@ class PhpProcess extends Process
      * @param int         $timeout The timeout in seconds
      * @param array|null  $php     Path to the PHP binary to use with any additional arguments
      */
-    public function __construct(string $script, string $cwd = null, array $env = null, int $timeout = 60, array $php = null)
+    public function __construct(string $script, ?string $cwd = null, ?array $env = null, int $timeout = 60, ?array $php = null)
     {
         if (null === $php) {
             $executableFinder = new PhpExecutableFinder();
@@ -53,7 +53,7 @@ public function __construct(string $script, string $cwd = null, array $env = nul
     /**
      * {@inheritdoc}
      */
-    public static function fromShellCommandline(string $command, string $cwd = null, array $env = null, $input = null, ?float $timeout = 60)
+    public static function fromShellCommandline(string $command, ?string $cwd = null, ?array $env = null, $input = null, ?float $timeout = 60)
     {
         throw new LogicException(sprintf('The "%s()" method cannot be called when using "%s".', __METHOD__, self::class));
     }
@@ -61,7 +61,7 @@ public static function fromShellCommandline(string $command, string $cwd = null,
     /**
      * {@inheritdoc}
      */
-    public function start(callable $callback = null, array $env = [])
+    public function start(?callable $callback = null, array $env = [])
     {
         if (null === $this->getCommandLine()) {
             throw new RuntimeException('Unable to find the PHP executable.');
diff --git a/Pipes/AbstractPipes.php b/Pipes/AbstractPipes.php
index 2d145872..656dc032 100644
--- a/Pipes/AbstractPipes.php
+++ b/Pipes/AbstractPipes.php
@@ -47,7 +47,9 @@ public function __construct($input)
     public function close()
     {
         foreach ($this->pipes as $pipe) {
-            fclose($pipe);
+            if (\is_resource($pipe)) {
+                fclose($pipe);
+            }
         }
         $this->pipes = [];
     }
@@ -102,7 +104,7 @@ protected function write(): ?array
                 stream_set_blocking($input, 0);
             } elseif (!isset($this->inputBuffer[0])) {
                 if (!\is_string($input)) {
-                    if (!is_scalar($input)) {
+                    if (!\is_scalar($input)) {
                         throw new InvalidArgumentException(sprintf('"%s" yielded a value of type "%s", but only scalars and stream resources are supported.', get_debug_type($this->input), get_debug_type($input)));
                     }
                     $input = (string) $input;
@@ -133,7 +135,7 @@ protected function write(): ?array
             }
 
             if ($input) {
-                for (;;) {
+                while (true) {
                     $data = fread($input, self::CHUNK_SIZE);
                     if (!isset($data[0])) {
                         break;
diff --git a/Pipes/UnixPipes.php b/Pipes/UnixPipes.php
index 58a8da07..5a0e9d47 100644
--- a/Pipes/UnixPipes.php
+++ b/Pipes/UnixPipes.php
@@ -35,10 +35,7 @@ public function __construct(?bool $ttyMode, bool $ptyMode, $input, bool $haveRea
         parent::__construct($input);
     }
 
-    /**
-     * @return array
-     */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
diff --git a/Pipes/WindowsPipes.php b/Pipes/WindowsPipes.php
index 69768f3d..968dd026 100644
--- a/Pipes/WindowsPipes.php
+++ b/Pipes/WindowsPipes.php
@@ -88,10 +88,7 @@ public function __construct($input, bool $haveReadSupport)
         parent::__construct($input);
     }
 
-    /**
-     * @return array
-     */
-    public function __sleep()
+    public function __sleep(): array
     {
         throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
     }
@@ -152,7 +149,7 @@ public function readAndWrite(bool $blocking, bool $close = false): array
             if ($w) {
                 @stream_select($r, $w, $e, 0, Process::TIMEOUT_PRECISION * 1E6);
             } elseif ($this->fileHandles) {
-                usleep(Process::TIMEOUT_PRECISION * 1E6);
+                usleep((int) (Process::TIMEOUT_PRECISION * 1E6));
             }
         }
         foreach ($this->fileHandles as $type => $fileHandle) {
diff --git a/Process.php b/Process.php
index a541cd66..91f9e8fe 100644
--- a/Process.php
+++ b/Process.php
@@ -27,6 +27,8 @@
  *
  * @author Fabien Potencier <fabien@symfony.com>
  * @author Romain Neutron <imprec@gmail.com>
+ *
+ * @implements \IteratorAggregate<string, string>
  */
 class Process implements \IteratorAggregate
 {
@@ -53,7 +55,7 @@ class Process implements \IteratorAggregate
     private $hasCallback = false;
     private $commandline;
     private $cwd;
-    private $env;
+    private $env = [];
     private $input;
     private $starttime;
     private $lastOutputTime;
@@ -78,6 +80,7 @@ class Process implements \IteratorAggregate
     private $processPipes;
 
     private $latestSignal;
+    private $cachedExitCode;
 
     private static $sigchild;
 
@@ -138,7 +141,7 @@ class Process implements \IteratorAggregate
      *
      * @throws LogicException When proc_open is not installed
      */
-    public function __construct(array $command, string $cwd = null, array $env = null, $input = null, ?float $timeout = 60)
+    public function __construct(array $command, ?string $cwd = null, ?array $env = null, $input = null, ?float $timeout = 60)
     {
         if (!\function_exists('proc_open')) {
             throw new LogicException('The Process class relies on proc_open, which is not available on your PHP installation.');
@@ -174,7 +177,7 @@ public function __construct(array $command, string $cwd = null, array $env = nul
      * In order to inject dynamic values into command-lines, we strongly recommend using placeholders.
      * This will save escaping values, which is not portable nor secure anyway:
      *
-     *   $process = Process::fromShellCommandline('my_command "$MY_VAR"');
+     *   $process = Process::fromShellCommandline('my_command "${:MY_VAR}"');
      *   $process->run(null, ['MY_VAR' => $theValue]);
      *
      * @param string         $command The command line to pass to the shell of the OS
@@ -187,7 +190,7 @@ public function __construct(array $command, string $cwd = null, array $env = nul
      *
      * @throws LogicException When proc_open is not installed
      */
-    public static function fromShellCommandline(string $command, string $cwd = null, array $env = null, $input = null, ?float $timeout = 60)
+    public static function fromShellCommandline(string $command, ?string $cwd = null, ?array $env = null, $input = null, ?float $timeout = 60)
     {
         $process = new static([], $cwd, $env, $input, $timeout);
         $process->commandline = $command;
@@ -245,7 +248,7 @@ public function __clone()
      *
      * @final
      */
-    public function run(callable $callback = null, array $env = []): int
+    public function run(?callable $callback = null, array $env = []): int
     {
         $this->start($callback, $env);
 
@@ -264,7 +267,7 @@ public function run(callable $callback = null, array $env = []): int
      *
      * @final
      */
-    public function mustRun(callable $callback = null, array $env = []): self
+    public function mustRun(?callable $callback = null, array $env = []): self
     {
         if (0 !== $this->run($callback, $env)) {
             throw new ProcessFailedException($this);
@@ -292,7 +295,7 @@ public function mustRun(callable $callback = null, array $env = []): self
      * @throws RuntimeException When process is already running
      * @throws LogicException   In case a callback is provided and output has been disabled
      */
-    public function start(callable $callback = null, array $env = [])
+    public function start(?callable $callback = null, array $env = [])
     {
         if ($this->isRunning()) {
             throw new RuntimeException('Process is already running.');
@@ -305,10 +308,10 @@ public function start(callable $callback = null, array $env = [])
         $descriptors = $this->getDescriptors();
 
         if ($this->env) {
-            $env += $this->env;
+            $env += '\\' === \DIRECTORY_SEPARATOR ? array_diff_ukey($this->env, $env, 'strcasecmp') : $this->env;
         }
 
-        $env += $this->getDefaultEnv();
+        $env += '\\' === \DIRECTORY_SEPARATOR ? array_diff_ukey($this->getDefaultEnv(), $env, 'strcasecmp') : $this->getDefaultEnv();
 
         if (\is_array($commandline = $this->commandline)) {
             $commandline = implode(' ', array_map([$this, 'escapeArgument'], $commandline));
@@ -329,7 +332,7 @@ public function start(callable $callback = null, array $env = [])
 
             // See https://unix.stackexchange.com/questions/71205/background-process-pipe-input
             $commandline = '{ ('.$commandline.') <&3 3<&- 3>/dev/null & } 3<&0;';
-            $commandline .= 'pid=$!; echo $pid >&3; wait $pid; code=$?; echo $code >&3; exit $code';
+            $commandline .= 'pid=$!; echo $pid >&3; wait $pid 2>/dev/null; code=$?; echo $code >&3; exit $code';
 
             // Workaround for the bug, when PTS functionality is enabled.
             // @see : https://bugs.php.net/69442
@@ -338,7 +341,7 @@ public function start(callable $callback = null, array $env = [])
 
         $envPairs = [];
         foreach ($env as $k => $v) {
-            if (false !== $v) {
+            if (false !== $v && false === \in_array($k, ['argc', 'argv', 'ARGC', 'ARGV'], true)) {
                 $envPairs[] = $k.'='.$v;
             }
         }
@@ -349,7 +352,7 @@ public function start(callable $callback = null, array $env = [])
 
         $this->process = @proc_open($commandline, $descriptors, $this->processPipes->pipes, $this->cwd, $envPairs, $this->options);
 
-        if (!\is_resource($this->process)) {
+        if (!$this->process) {
             throw new RuntimeException('Unable to launch a new process.');
         }
         $this->status = self::STATUS_STARTED;
@@ -383,7 +386,7 @@ public function start(callable $callback = null, array $env = [])
      *
      * @final
      */
-    public function restart(callable $callback = null, array $env = []): self
+    public function restart(?callable $callback = null, array $env = []): self
     {
         if ($this->isRunning()) {
             throw new RuntimeException('Process is already running.');
@@ -410,7 +413,7 @@ public function restart(callable $callback = null, array $env = []): self
      * @throws ProcessSignaledException When process stopped after receiving signal
      * @throws LogicException           When process is not yet started
      */
-    public function wait(callable $callback = null)
+    public function wait(?callable $callback = null)
     {
         $this->requireProcessIsStarted(__FUNCTION__);
 
@@ -426,7 +429,7 @@ public function wait(callable $callback = null)
 
         do {
             $this->checkTimeout();
-            $running = '\\' === \DIRECTORY_SEPARATOR ? $this->isRunning() : $this->processPipes->areOpen();
+            $running = $this->isRunning() && ('\\' === \DIRECTORY_SEPARATOR || $this->processPipes->areOpen());
             $this->readPipes($running, '\\' !== \DIRECTORY_SEPARATOR || !$running);
         } while ($running);
 
@@ -530,7 +533,7 @@ public function disableOutput()
             throw new RuntimeException('Disabling output while the process is running is not possible.');
         }
         if (null !== $this->idleTimeout) {
-            throw new LogicException('Output can not be disabled while an idle timeout is set.');
+            throw new LogicException('Output cannot be disabled while an idle timeout is set.');
         }
 
         $this->outputDisabled = true;
@@ -569,7 +572,7 @@ public function isOutputDisabled()
     /**
      * Returns the current output of the process (STDOUT).
      *
-     * @return string The process output
+     * @return string
      *
      * @throws LogicException in case the output has been disabled
      * @throws LogicException In case the process is not started
@@ -591,7 +594,7 @@ public function getOutput()
      * In comparison with the getOutput method which always return the whole
      * output, this one returns the new output since the last call.
      *
-     * @return string The process output since the last call
+     * @return string
      *
      * @throws LogicException in case the output has been disabled
      * @throws LogicException In case the process is not started
@@ -615,10 +618,10 @@ public function getIncrementalOutput()
      *
      * @param int $flags A bit field of Process::ITER_* flags
      *
+     * @return \Generator<string, string>
+     *
      * @throws LogicException in case the output has been disabled
      * @throws LogicException In case the process is not started
-     *
-     * @return \Generator
      */
     #[\ReturnTypeWillChange]
     public function getIterator(int $flags = 0)
@@ -685,7 +688,7 @@ public function clearOutput()
     /**
      * Returns the current error output of the process (STDERR).
      *
-     * @return string The process error output
+     * @return string
      *
      * @throws LogicException in case the output has been disabled
      * @throws LogicException In case the process is not started
@@ -708,7 +711,7 @@ public function getErrorOutput()
      * whole error output, this one returns the new error output since the last
      * call.
      *
-     * @return string The process error output since the last call
+     * @return string
      *
      * @throws LogicException in case the output has been disabled
      * @throws LogicException In case the process is not started
@@ -776,7 +779,7 @@ public function getExitCodeText()
     /**
      * Checks if the process ended successfully.
      *
-     * @return bool true if the process ended successfully, false otherwise
+     * @return bool
      */
     public function isSuccessful()
     {
@@ -814,7 +817,7 @@ public function getTermSignal()
         $this->requireProcessIsTerminated(__FUNCTION__);
 
         if ($this->isSigchildEnabled() && -1 === $this->processInformation['termsig']) {
-            throw new RuntimeException('This PHP has been compiled with --enable-sigchild. Term signal can not be retrieved.');
+            throw new RuntimeException('This PHP has been compiled with --enable-sigchild. Term signal cannot be retrieved.');
         }
 
         return $this->processInformation['termsig'];
@@ -855,7 +858,7 @@ public function getStopSignal()
     /**
      * Checks if the process is currently running.
      *
-     * @return bool true if the process is currently running, false otherwise
+     * @return bool
      */
     public function isRunning()
     {
@@ -871,7 +874,7 @@ public function isRunning()
     /**
      * Checks if the process has been started with no regard to the current state.
      *
-     * @return bool true if status is ready, false otherwise
+     * @return bool
      */
     public function isStarted()
     {
@@ -881,7 +884,7 @@ public function isStarted()
     /**
      * Checks if the process is terminated.
      *
-     * @return bool true if process is terminated, false otherwise
+     * @return bool
      */
     public function isTerminated()
     {
@@ -895,7 +898,7 @@ public function isTerminated()
      *
      * The status is one of: ready, started, terminated.
      *
-     * @return string The current process status
+     * @return string
      */
     public function getStatus()
     {
@@ -908,11 +911,11 @@ public function getStatus()
      * Stops the process.
      *
      * @param int|float $timeout The timeout in seconds
-     * @param int       $signal  A POSIX signal to send in case the process has not stop at timeout, default is SIGKILL (9)
+     * @param int|null  $signal  A POSIX signal to send in case the process has not stop at timeout, default is SIGKILL (9)
      *
      * @return int|null The exit-code of the process or null if it's not running
      */
-    public function stop(float $timeout = 10, int $signal = null)
+    public function stop(float $timeout = 10, ?int $signal = null)
     {
         $timeoutMicro = microtime(true) + $timeout;
         if ($this->isRunning()) {
@@ -971,8 +974,6 @@ public function addErrorOutput(string $line)
 
     /**
      * Gets the last output time in seconds.
-     *
-     * @return float|null The last output time in seconds or null if it isn't started
      */
     public function getLastOutputTime(): ?float
     {
@@ -982,7 +983,7 @@ public function getLastOutputTime(): ?float
     /**
      * Gets the command line to be executed.
      *
-     * @return string The command to execute
+     * @return string
      */
     public function getCommandLine()
     {
@@ -990,9 +991,9 @@ public function getCommandLine()
     }
 
     /**
-     * Gets the process timeout (max. runtime).
+     * Gets the process timeout in seconds (max. runtime).
      *
-     * @return float|null The timeout in seconds or null if it's disabled
+     * @return float|null
      */
     public function getTimeout()
     {
@@ -1000,9 +1001,9 @@ public function getTimeout()
     }
 
     /**
-     * Gets the process idle timeout (max. time since last output).
+     * Gets the process idle timeout in seconds (max. time since last output).
      *
-     * @return float|null The timeout in seconds or null if it's disabled
+     * @return float|null
      */
     public function getIdleTimeout()
     {
@@ -1038,7 +1039,7 @@ public function setTimeout(?float $timeout)
     public function setIdleTimeout(?float $timeout)
     {
         if (null !== $timeout && $this->outputDisabled) {
-            throw new LogicException('Idle timeout can not be set while the output is disabled.');
+            throw new LogicException('Idle timeout cannot be set while the output is disabled.');
         }
 
         $this->idleTimeout = $this->validateTimeout($timeout);
@@ -1071,7 +1072,7 @@ public function setTty(bool $tty)
     /**
      * Checks if the TTY mode is enabled.
      *
-     * @return bool true if the TTY mode is enabled, false otherwise
+     * @return bool
      */
     public function isTty()
     {
@@ -1103,7 +1104,7 @@ public function isPty()
     /**
      * Gets the working directory.
      *
-     * @return string|null The current working directory or null on failure
+     * @return string|null
      */
     public function getWorkingDirectory()
     {
@@ -1131,7 +1132,7 @@ public function setWorkingDirectory(string $cwd)
     /**
      * Gets the environment variables.
      *
-     * @return array The current environment variables
+     * @return array
      */
     public function getEnv()
     {
@@ -1141,25 +1142,12 @@ public function getEnv()
     /**
      * Sets the environment variables.
      *
-     * Each environment variable value should be a string.
-     * If it is an array, the variable is ignored.
-     * If it is false or null, it will be removed when
-     * env vars are otherwise inherited.
-     *
-     * That happens in PHP when 'argv' is registered into
-     * the $_ENV array for instance.
-     *
-     * @param array $env The new environment variables
+     * @param array<string|\Stringable> $env The new environment variables
      *
      * @return $this
      */
     public function setEnv(array $env)
     {
-        // Process can not handle env values that are arrays
-        $env = array_filter($env, function ($value) {
-            return !\is_array($value);
-        });
-
         $this->env = $env;
 
         return $this;
@@ -1168,7 +1156,7 @@ public function setEnv(array $env)
     /**
      * Gets the Process input.
      *
-     * @return resource|string|\Iterator|null The Process input
+     * @return resource|string|\Iterator|null
      */
     public function getInput()
     {
@@ -1189,7 +1177,7 @@ public function getInput()
     public function setInput($input)
     {
         if ($this->isRunning()) {
-            throw new LogicException('Input can not be set while the process is running.');
+            throw new LogicException('Input cannot be set while the process is running.');
         }
 
         $this->input = ProcessUtils::validateInput(__METHOD__, $input);
@@ -1321,9 +1309,9 @@ private function getDescriptors(): array
      *
      * @param callable|null $callback The user defined PHP callback
      *
-     * @return \Closure A PHP closure
+     * @return \Closure
      */
-    protected function buildCallback(callable $callback = null)
+    protected function buildCallback(?callable $callback = null)
     {
         if ($this->outputDisabled) {
             return function ($type, $data) use ($callback): bool {
@@ -1358,6 +1346,19 @@ protected function updateStatus(bool $blocking)
         $this->processInformation = proc_get_status($this->process);
         $running = $this->processInformation['running'];
 
+        // In PHP < 8.3, "proc_get_status" only returns the correct exit status on the first call.
+        // Subsequent calls return -1 as the process is discarded. This workaround caches the first
+        // retrieved exit status for consistent results in later calls, mimicking PHP 8.3 behavior.
+        if (\PHP_VERSION_ID < 80300) {
+            if (!isset($this->cachedExitCode) && !$running && -1 !== $this->processInformation['exitcode']) {
+                $this->cachedExitCode = $this->processInformation['exitcode'];
+            }
+
+            if (isset($this->cachedExitCode) && !$running && -1 === $this->processInformation['exitcode']) {
+                $this->processInformation['exitcode'] = $this->cachedExitCode;
+            }
+        }
+
         $this->readPipes($running && $blocking, '\\' !== \DIRECTORY_SEPARATOR || !$running);
 
         if ($this->fallbackStatus && $this->isSigchildEnabled()) {
@@ -1455,8 +1456,9 @@ private function readPipes(bool $blocking, bool $close)
     private function close(): int
     {
         $this->processPipes->close();
-        if (\is_resource($this->process)) {
+        if ($this->process) {
             proc_close($this->process);
+            $this->process = null;
         }
         $this->exitcode = $this->processInformation['exitcode'];
         $this->status = self::STATUS_TERMINATED;
@@ -1504,8 +1506,6 @@ private function resetProcessData()
      * @param int  $signal         A valid POSIX signal (see https://php.net/pcntl.constants)
      * @param bool $throwException Whether to throw exception in case signal failed
      *
-     * @return bool True if the signal was sent successfully, false otherwise
-     *
      * @throws LogicException   In case the process is not running
      * @throws RuntimeException In case --enable-sigchild is activated and the process can't be killed
      * @throws RuntimeException In case of failure
@@ -1514,7 +1514,7 @@ private function doSignal(int $signal, bool $throwException): bool
     {
         if (null === $pid = $this->getPid()) {
             if ($throwException) {
-                throw new LogicException('Can not send signal on a non running process.');
+                throw new LogicException('Cannot send signal on a non running process.');
             }
 
             return false;
@@ -1592,7 +1592,14 @@ function ($m) use (&$env, &$varCache, &$varCount, $uid) {
             $cmd
         );
 
-        $cmd = 'cmd /V:ON /E:ON /D /C ('.str_replace("\n", ' ', $cmd).')';
+        static $comSpec;
+
+        if (!$comSpec && $comSpec = (new ExecutableFinder())->find('cmd.exe')) {
+            // Escape according to CommandLineToArgvW rules
+            $comSpec = '"'.preg_replace('{(\\\\*+)"}', '$1$1\"', $comSpec) .'"';
+        }
+
+        $cmd = ($comSpec ?? 'cmd').' /V:ON /E:ON /D /C ('.str_replace("\n", ' ', $cmd).')';
         foreach ($this->processPipes->getFiles() as $offset => $filename) {
             $cmd .= ' '.$offset.'>"'.$filename.'"';
         }
@@ -1638,7 +1645,7 @@ private function escapeArgument(?string $argument): string
         if (str_contains($argument, "\0")) {
             $argument = str_replace("\0", '?', $argument);
         }
-        if (!preg_match('/[\/()%!^"<>&|\s]/', $argument)) {
+        if (!preg_match('/[()%!^"<>&|\s]/', $argument)) {
             return $argument;
         }
         $argument = preg_replace('/(\\\\+)$/', '$1$1', $argument);
@@ -1659,20 +1666,9 @@ private function replacePlaceholders(string $commandline, array $env)
 
     private function getDefaultEnv(): array
     {
-        $env = [];
-
-        foreach ($_SERVER as $k => $v) {
-            if (\is_string($v) && false !== $v = getenv($k)) {
-                $env[$k] = $v;
-            }
-        }
-
-        foreach ($_ENV as $k => $v) {
-            if (\is_string($v)) {
-                $env[$k] = $v;
-            }
-        }
+        $env = getenv();
+        $env = ('\\' === \DIRECTORY_SEPARATOR ? array_intersect_ukey($env, $_SERVER, 'strcasecmp') : array_intersect_key($env, $_SERVER)) ?: $env;
 
-        return $env;
+        return $_ENV + ('\\' === \DIRECTORY_SEPARATOR ? array_diff_ukey($env, $_ENV, 'strcasecmp') : $env);
     }
 }
diff --git a/ProcessUtils.php b/ProcessUtils.php
index 3be7e61a..2a7aff71 100644
--- a/ProcessUtils.php
+++ b/ProcessUtils.php
@@ -35,7 +35,7 @@ private function __construct()
      * @param string $caller The name of method call that validates the input
      * @param mixed  $input  The input to validate
      *
-     * @return mixed The validated input
+     * @return mixed
      *
      * @throws InvalidArgumentException In case the input is not valid
      */
@@ -48,7 +48,7 @@ public static function validateInput(string $caller, $input)
             if (\is_string($input)) {
                 return $input;
             }
-            if (is_scalar($input)) {
+            if (\is_scalar($input)) {
                 return (string) $input;
             }
             if ($input instanceof Process) {
diff --git a/README.md b/README.md
index afce5e45..8777de4a 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,17 @@ Process Component
 
 The Process component executes commands in sub-processes.
 
+Sponsor
+-------
+
+The Process component for Symfony 5.4/6.0 is [backed][1] by [SensioLabs][2].
+
+As the creator of Symfony, SensioLabs supports companies using Symfony, with an
+offering encompassing consultancy, expertise, services, training, and technical
+assistance to ensure the success of web application development projects.
+
+Help Symfony by [sponsoring][3] its development!
+
 Resources
 ---------
 
@@ -11,3 +22,7 @@ Resources
  * [Report issues](https://github.com/symfony/symfony/issues) and
    [send Pull Requests](https://github.com/symfony/symfony/pulls)
    in the [main Symfony repository](https://github.com/symfony/symfony)
+
+[1]: https://symfony.com/backers
+[2]: https://sensiolabs.com
+[3]: https://symfony.com/sponsor
diff --git a/Tests/ErrorProcessInitiator.php b/Tests/ErrorProcessInitiator.php
old mode 100755
new mode 100644
index 4c8556ac..0b75add6
--- a/Tests/ErrorProcessInitiator.php
+++ b/Tests/ErrorProcessInitiator.php
@@ -14,18 +14,18 @@
 use Symfony\Component\Process\Exception\ProcessTimedOutException;
 use Symfony\Component\Process\Process;
 
-require \dirname(__DIR__).'/vendor/autoload.php';
+require is_file(\dirname(__DIR__).'/vendor/autoload.php') ? \dirname(__DIR__).'/vendor/autoload.php' : \dirname(__DIR__, 5).'/vendor/autoload.php';
 
 ['e' => $php] = getopt('e:') + ['e' => 'php'];
 
 try {
-    $process = new Process("exec $php -r \"echo 'ready'; trigger_error('error', E_USER_ERROR);\"");
+    $process = new Process([$php, '-r', "echo 'ready'; trigger_error('error', E_USER_ERROR);"]);
     $process->start();
     $process->setTimeout(0.5);
     while (!str_contains($process->getOutput(), 'ready')) {
         usleep(1000);
     }
-    $process->signal(\SIGSTOP);
+    $process->isRunning() && $process->signal(\SIGSTOP);
     $process->wait();
 
     return $process->getExitCode();
diff --git a/Tests/ExecutableFinderTest.php b/Tests/ExecutableFinderTest.php
index 83f263ff..84e5b3c3 100644
--- a/Tests/ExecutableFinderTest.php
+++ b/Tests/ExecutableFinderTest.php
@@ -19,29 +19,18 @@
  */
 class ExecutableFinderTest extends TestCase
 {
-    private $path;
-
     protected function tearDown(): void
     {
-        if ($this->path) {
-            // Restore path if it was changed.
-            putenv('PATH='.$this->path);
-        }
-    }
-
-    private function setPath($path)
-    {
-        $this->path = getenv('PATH');
-        putenv('PATH='.$path);
+        putenv('PATH='.($_SERVER['PATH'] ?? $_SERVER['Path']));
     }
 
     public function testFind()
     {
-        if (ini_get('open_basedir')) {
+        if (\ini_get('open_basedir')) {
             $this->markTestSkipped('Cannot test when open_basedir is set');
         }
 
-        $this->setPath(\dirname(\PHP_BINARY));
+        putenv('PATH='.\dirname(\PHP_BINARY));
 
         $finder = new ExecutableFinder();
         $result = $finder->find($this->getPhpBinaryName());
@@ -51,13 +40,13 @@ public function testFind()
 
     public function testFindWithDefault()
     {
-        if (ini_get('open_basedir')) {
+        if (\ini_get('open_basedir')) {
             $this->markTestSkipped('Cannot test when open_basedir is set');
         }
 
         $expected = 'defaultValue';
 
-        $this->setPath('');
+        putenv('PATH=');
 
         $finder = new ExecutableFinder();
         $result = $finder->find('foo', $expected);
@@ -67,11 +56,11 @@ public function testFindWithDefault()
 
     public function testFindWithNullAsDefault()
     {
-        if (ini_get('open_basedir')) {
+        if (\ini_get('open_basedir')) {
             $this->markTestSkipped('Cannot test when open_basedir is set');
         }
 
-        $this->setPath('');
+        putenv('PATH=');
 
         $finder = new ExecutableFinder();
 
@@ -82,11 +71,11 @@ public function testFindWithNullAsDefault()
 
     public function testFindWithExtraDirs()
     {
-        if (ini_get('open_basedir')) {
+        if (\ini_get('open_basedir')) {
             $this->markTestSkipped('Cannot test when open_basedir is set');
         }
 
-        $this->setPath('');
+        putenv('PATH=');
 
         $extraDirs = [\dirname(\PHP_BINARY)];
 
@@ -96,67 +85,94 @@ public function testFindWithExtraDirs()
         $this->assertSamePath(\PHP_BINARY, $result);
     }
 
+    /**
+     * @runInSeparateProcess
+     */
     public function testFindWithOpenBaseDir()
     {
         if ('\\' === \DIRECTORY_SEPARATOR) {
             $this->markTestSkipped('Cannot run test on windows');
         }
 
-        if (ini_get('open_basedir')) {
+        if (\ini_get('open_basedir')) {
             $this->markTestSkipped('Cannot test when open_basedir is set');
         }
 
-        $this->iniSet('open_basedir', \dirname(\PHP_BINARY).\PATH_SEPARATOR.'/');
+        putenv('PATH='.\dirname(\PHP_BINARY));
+        $initialOpenBaseDir = ini_set('open_basedir', \dirname(\PHP_BINARY).\PATH_SEPARATOR.'/');
 
-        $finder = new ExecutableFinder();
-        $result = $finder->find($this->getPhpBinaryName());
+        try {
+            $finder = new ExecutableFinder();
+            $result = $finder->find($this->getPhpBinaryName());
 
-        $this->assertSamePath(\PHP_BINARY, $result);
+            $this->assertSamePath(\PHP_BINARY, $result);
+        } finally {
+            ini_set('open_basedir', $initialOpenBaseDir);
+        }
     }
 
-    public function testFindProcessInOpenBasedir()
+    /**
+     * @runInSeparateProcess
+     */
+    public function testFindBatchExecutableOnWindows()
     {
-        if (ini_get('open_basedir')) {
+        if (\ini_get('open_basedir')) {
             $this->markTestSkipped('Cannot test when open_basedir is set');
         }
-        if ('\\' === \DIRECTORY_SEPARATOR) {
-            $this->markTestSkipped('Cannot run test on windows');
+        if ('\\' !== \DIRECTORY_SEPARATOR) {
+            $this->markTestSkipped('Can be only tested on windows');
         }
 
-        $this->setPath('');
-        $this->iniSet('open_basedir', \PHP_BINARY.\PATH_SEPARATOR.'/');
+        $target = str_replace('.tmp', '_tmp', tempnam(sys_get_temp_dir(), 'example-windows-executable'));
 
-        $finder = new ExecutableFinder();
-        $result = $finder->find($this->getPhpBinaryName(), false);
+        try {
+            touch($target);
+            touch($target.'.BAT');
 
-        $this->assertSamePath(\PHP_BINARY, $result);
-    }
+            $this->assertFalse(is_executable($target));
 
-    public function testFindBatchExecutableOnWindows()
-    {
-        if (ini_get('open_basedir')) {
-            $this->markTestSkipped('Cannot test when open_basedir is set');
-        }
-        if ('\\' !== \DIRECTORY_SEPARATOR) {
-            $this->markTestSkipped('Can be only tested on windows');
+            putenv('PATH='.sys_get_temp_dir());
+
+            $finder = new ExecutableFinder();
+            $result = $finder->find(basename($target), false);
+        } finally {
+            unlink($target);
+            unlink($target.'.BAT');
         }
 
-        $target = tempnam(sys_get_temp_dir(), 'example-windows-executable');
+        $this->assertSamePath($target.'.BAT', $result);
+    }
 
-        touch($target);
-        touch($target.'.BAT');
+    /**
+     * @runInSeparateProcess
+     */
+    public function testEmptyDirInPath()
+    {
+        putenv(sprintf('PATH=%s%s', \dirname(\PHP_BINARY), \PATH_SEPARATOR));
 
-        $this->assertFalse(is_executable($target));
+        try {
+            touch('executable');
+            chmod('executable', 0700);
 
-        $this->setPath(sys_get_temp_dir());
+            $finder = new ExecutableFinder();
+            $result = $finder->find('executable');
 
-        $finder = new ExecutableFinder();
-        $result = $finder->find(basename($target), false);
+            $this->assertSame(sprintf('.%sexecutable', \DIRECTORY_SEPARATOR), $result);
+        } finally {
+            unlink('executable');
+        }
+    }
 
-        unlink($target);
-        unlink($target.'.BAT');
+    public function testFindBuiltInCommandOnWindows()
+    {
+        if ('\\' !== \DIRECTORY_SEPARATOR) {
+            $this->markTestSkipped('Can be only tested on windows');
+        }
 
-        $this->assertSamePath($target.'.BAT', $result);
+        $finder = new ExecutableFinder();
+        $this->assertSame('rmdir', strtolower($finder->find('RMDIR')));
+        $this->assertSame('cd', strtolower($finder->find('cd')));
+        $this->assertSame('move', strtolower($finder->find('MoVe')));
     }
 
     private function assertSamePath($expected, $tested)
diff --git a/Tests/PhpExecutableFinderTest.php b/Tests/PhpExecutableFinderTest.php
index cf3ffb55..23de6d42 100644
--- a/Tests/PhpExecutableFinderTest.php
+++ b/Tests/PhpExecutableFinderTest.php
@@ -50,12 +50,36 @@ public function testFindArguments()
     public function testNotExitsBinaryFile()
     {
         $f = new PhpExecutableFinder();
-        $phpBinaryEnv = \PHP_BINARY;
-        putenv('PHP_BINARY=/usr/local/php/bin/php-invalid');
 
-        $this->assertFalse($f->find(), '::find() returns false because of not exist file');
-        $this->assertFalse($f->find(false), '::find(false) returns false because of not exist file');
+        $originalPhpBinary = getenv('PHP_BINARY');
 
-        putenv('PHP_BINARY='.$phpBinaryEnv);
+        try {
+            putenv('PHP_BINARY=/usr/local/php/bin/php-invalid');
+
+            $this->assertFalse($f->find(), '::find() returns false because of not exist file');
+            $this->assertFalse($f->find(false), '::find(false) returns false because of not exist file');
+        } finally {
+            putenv('PHP_BINARY='.$originalPhpBinary);
+        }
+    }
+
+    public function testFindWithExecutableDirectory()
+    {
+        if ('\\' === \DIRECTORY_SEPARATOR) {
+            $this->markTestSkipped('Directories are not executable on Windows');
+        }
+
+        $originalPhpBinary = getenv('PHP_BINARY');
+
+        try {
+            $executableDirectoryPath = sys_get_temp_dir().'/PhpExecutableFinderTest_testFindWithExecutableDirectory';
+            @mkdir($executableDirectoryPath);
+            $this->assertTrue(is_executable($executableDirectoryPath));
+            putenv('PHP_BINARY='.$executableDirectoryPath);
+
+            $this->assertFalse((new PhpExecutableFinder())->find());
+        } finally {
+            putenv('PHP_BINARY='.$originalPhpBinary);
+        }
     }
 }
diff --git a/Tests/PipeStdinInStdoutStdErrStreamSelect.php b/Tests/PipeStdinInStdoutStdErrStreamSelect.php
index a206d2b8..09124a4b 100644
--- a/Tests/PipeStdinInStdoutStdErrStreamSelect.php
+++ b/Tests/PipeStdinInStdoutStdErrStreamSelect.php
@@ -34,7 +34,7 @@
         exit(ERR_TIMEOUT);
     }
 
-    if (in_array(\STDOUT, $w) && strlen($out) > 0) {
+    if (in_array(\STDOUT, $w) && '' !== $out) {
         $written = fwrite(\STDOUT, (string) $out, 32768);
         if (false === $written) {
             exit(ERR_WRITE_FAILED);
@@ -45,7 +45,7 @@
         $write = array_diff($write, [\STDOUT]);
     }
 
-    if (in_array(\STDERR, $w) && strlen($err) > 0) {
+    if (in_array(\STDERR, $w) && '' !== $err) {
         $written = fwrite(\STDERR, (string) $err, 32768);
         if (false === $written) {
             exit(ERR_WRITE_FAILED);
diff --git a/Tests/ProcessFailedExceptionTest.php b/Tests/ProcessFailedExceptionTest.php
index d6d7bfb0..259ffd63 100644
--- a/Tests/ProcessFailedExceptionTest.php
+++ b/Tests/ProcessFailedExceptionTest.php
@@ -25,7 +25,7 @@ class ProcessFailedExceptionTest extends TestCase
      */
     public function testProcessFailedExceptionThrowsException()
     {
-        $process = $this->getMockBuilder(Process::class)->setMethods(['isSuccessful'])->setConstructorArgs([['php']])->getMock();
+        $process = $this->getMockBuilder(Process::class)->onlyMethods(['isSuccessful'])->setConstructorArgs([['php']])->getMock();
         $process->expects($this->once())
             ->method('isSuccessful')
             ->willReturn(true);
@@ -49,7 +49,7 @@ public function testProcessFailedExceptionPopulatesInformationFromProcessOutput(
         $errorOutput = 'FATAL: Unexpected error';
         $workingDirectory = getcwd();
 
-        $process = $this->getMockBuilder(Process::class)->setMethods(['isSuccessful', 'getOutput', 'getErrorOutput', 'getExitCode', 'getExitCodeText', 'isOutputDisabled', 'getWorkingDirectory'])->setConstructorArgs([[$cmd]])->getMock();
+        $process = $this->getMockBuilder(Process::class)->onlyMethods(['isSuccessful', 'getOutput', 'getErrorOutput', 'getExitCode', 'getExitCodeText', 'isOutputDisabled', 'getWorkingDirectory'])->setConstructorArgs([[$cmd]])->getMock();
         $process->expects($this->once())
             ->method('isSuccessful')
             ->willReturn(false);
@@ -97,7 +97,7 @@ public function testDisabledOutputInFailedExceptionDoesNotPopulateOutput()
         $exitText = 'General error';
         $workingDirectory = getcwd();
 
-        $process = $this->getMockBuilder(Process::class)->setMethods(['isSuccessful', 'isOutputDisabled', 'getExitCode', 'getExitCodeText', 'getOutput', 'getErrorOutput', 'getWorkingDirectory'])->setConstructorArgs([[$cmd]])->getMock();
+        $process = $this->getMockBuilder(Process::class)->onlyMethods(['isSuccessful', 'isOutputDisabled', 'getExitCode', 'getExitCodeText', 'getOutput', 'getErrorOutput', 'getWorkingDirectory'])->setConstructorArgs([[$cmd]])->getMock();
         $process->expects($this->once())
             ->method('isSuccessful')
             ->willReturn(false);
diff --git a/Tests/ProcessTest.php b/Tests/ProcessTest.php
index 70b8e051..e4d92874 100644
--- a/Tests/ProcessTest.php
+++ b/Tests/ProcessTest.php
@@ -66,11 +66,11 @@ public function testInvalidCwd()
         $cmd->run();
     }
 
+    /**
+     * @group transient-on-windows
+     */
     public function testThatProcessDoesNotThrowWarningDuringRun()
     {
-        if ('\\' === \DIRECTORY_SEPARATOR) {
-            $this->markTestSkipped('This test is transient on Windows');
-        }
         @trigger_error('Test Error', \E_USER_NOTICE);
         $process = $this->getProcessForCode('sleep(3)');
         $process->run();
@@ -130,12 +130,11 @@ public function testStopWithTimeoutIsActuallyWorking()
         $this->assertLessThan(15, microtime(true) - $start);
     }
 
+    /**
+     * @group transient-on-windows
+     */
     public function testWaitUntilSpecificOutput()
     {
-        if ('\\' === \DIRECTORY_SEPARATOR) {
-            $this->markTestIncomplete('This test is too transient on Windows, help wanted to improve it');
-        }
-
         $p = $this->getProcess([self::$phpBin, __DIR__.'/KillableProcessWithOutput.php']);
         $p->start();
 
@@ -276,7 +275,7 @@ public function testLiveStreamAsInput()
     public function testSetInputWhileRunningThrowsAnException()
     {
         $this->expectException(LogicException::class);
-        $this->expectExceptionMessage('Input can not be set while the process is running.');
+        $this->expectExceptionMessage('Input cannot be set while the process is running.');
         $process = $this->getProcessForCode('sleep(30);');
         $process->start();
         try {
@@ -301,7 +300,7 @@ public function testInvalidInput($value)
         $process->setInput($value);
     }
 
-    public function provideInvalidInputValues()
+    public static function provideInvalidInputValues()
     {
         return [
             [[]],
@@ -319,7 +318,7 @@ public function testValidInput($expected, $value)
         $this->assertSame($expected, $process->getInput());
     }
 
-    public function provideInputValues()
+    public static function provideInputValues()
     {
         return [
             [null, null],
@@ -328,7 +327,7 @@ public function provideInputValues()
         ];
     }
 
-    public function chainedCommandsOutputProvider()
+    public static function chainedCommandsOutputProvider()
     {
         if ('\\' === \DIRECTORY_SEPARATOR) {
             return [
@@ -422,7 +421,7 @@ public function testIncrementalOutput($getOutput, $getIncrementalOutput, $uri)
         fclose($h);
     }
 
-    public function provideIncrementalOutput()
+    public static function provideIncrementalOutput()
     {
         return [
             ['getOutput', 'getIncrementalOutput', 'php://stdout'],
@@ -772,7 +771,8 @@ public function testIterateOverProcessWithTimeout()
         $start = microtime(true);
         try {
             $process->start();
-            foreach ($process as $buffer);
+            foreach ($process as $buffer) {
+            }
             $this->fail('A RuntimeException should have been raised');
         } catch (RuntimeException $e) {
         }
@@ -938,7 +938,7 @@ public function testExitCodeIsAvailableAfterSignal()
     public function testSignalProcessNotRunning()
     {
         $this->expectException(LogicException::class);
-        $this->expectExceptionMessage('Can not send signal on a non running process.');
+        $this->expectExceptionMessage('Cannot send signal on a non running process.');
         $process = $this->getProcess('foo');
         $process->signal(1); // SIGHUP
     }
@@ -956,7 +956,7 @@ public function testMethodsThatNeedARunningProcess($method)
         $process->{$method}();
     }
 
-    public function provideMethodsThatNeedARunningProcess()
+    public static function provideMethodsThatNeedARunningProcess()
     {
         return [
             ['getOutput'],
@@ -987,7 +987,7 @@ public function testMethodsThatNeedATerminatedProcess($method)
         throw $e;
     }
 
-    public function provideMethodsThatNeedATerminatedProcess()
+    public static function provideMethodsThatNeedATerminatedProcess()
     {
         return [
             ['hasBeenSignaled'],
@@ -1057,7 +1057,7 @@ public function testEnableOrDisableOutputAfterRunDoesNotThrowException()
     public function testDisableOutputWhileIdleTimeoutIsSet()
     {
         $this->expectException(LogicException::class);
-        $this->expectExceptionMessage('Output can not be disabled while an idle timeout is set.');
+        $this->expectExceptionMessage('Output cannot be disabled while an idle timeout is set.');
         $process = $this->getProcess('foo');
         $process->setIdleTimeout(1);
         $process->disableOutput();
@@ -1066,7 +1066,7 @@ public function testDisableOutputWhileIdleTimeoutIsSet()
     public function testSetIdleTimeoutWhileOutputIsDisabled()
     {
         $this->expectException(LogicException::class);
-        $this->expectExceptionMessage('timeout can not be set while the output is disabled.');
+        $this->expectExceptionMessage('timeout cannot be set while the output is disabled.');
         $process = $this->getProcess('foo');
         $process->disableOutput();
         $process->setIdleTimeout(1);
@@ -1092,7 +1092,7 @@ public function testGetOutputWhileDisabled($fetchMethod)
         $p->{$fetchMethod}();
     }
 
-    public function provideOutputFetchingMethods()
+    public static function provideOutputFetchingMethods()
     {
         return [
             ['getOutput'],
@@ -1129,17 +1129,17 @@ public function testTermSignalTerminatesProcessCleanly()
         $this->assertTrue(true, 'A call to signal() is not expected to cause wait() to throw a RuntimeException');
     }
 
-    public function responsesCodeProvider()
+    public static function responsesCodeProvider()
     {
         return [
-            //expected output / getter / code to execute
+            // expected output / getter / code to execute
             // [1,'getExitCode','exit(1);'],
             // [true,'isSuccessful','exit();'],
             ['output', 'getOutput', 'echo \'output\';'],
         ];
     }
 
-    public function pipesCodeProvider()
+    public static function pipesCodeProvider()
     {
         $variations = [
             'fwrite(STDOUT, $in = file_get_contents(\'php://stdin\')); fwrite(STDERR, $in);',
@@ -1182,7 +1182,7 @@ public function testIncrementalOutputDoesNotRequireAnotherCall($stream, $method)
         $process->stop();
     }
 
-    public function provideVariousIncrementals()
+    public static function provideVariousIncrementals()
     {
         return [
             ['php://stdout', 'getIncrementalOutput'],
@@ -1424,7 +1424,12 @@ public function testGetCommandLine()
     {
         $p = new Process(['/usr/bin/php']);
 
-        $expected = '\\' === \DIRECTORY_SEPARATOR ? '"/usr/bin/php"' : "'/usr/bin/php'";
+        $expected = '\\' === \DIRECTORY_SEPARATOR ? '/usr/bin/php' : "'/usr/bin/php'";
+        $this->assertSame($expected, $p->getCommandLine());
+
+        $p = new Process(['cd', '/d']);
+
+        $expected = '\\' === \DIRECTORY_SEPARATOR ? 'cd /d' : "'cd' '/d'";
         $this->assertSame($expected, $p->getCommandLine());
     }
 
@@ -1448,7 +1453,7 @@ public function testRawCommandLine()
         $this->assertSame($expected, str_replace('Standard input code', '-', $p->getOutput()));
     }
 
-    public function provideEscapeArgument()
+    public static function provideEscapeArgument()
     {
         yield ['a"b%c%'];
         yield ['a"b^c^'];
@@ -1504,8 +1509,11 @@ public function testPreparedCommandWithNoValues()
 
     public function testEnvArgument()
     {
-        $env = ['FOO' => 'Foo', 'BAR' => 'Bar'];
         $cmd = '\\' === \DIRECTORY_SEPARATOR ? 'echo !FOO! !BAR! !BAZ!' : 'echo $FOO $BAR $BAZ';
+        $p = Process::fromShellCommandline($cmd);
+        $this->assertSame([], $p->getEnv());
+
+        $env = ['FOO' => 'Foo', 'BAR' => 'Bar'];
         $p = Process::fromShellCommandline($cmd, null, $env);
         $p->run(null, ['BAR' => 'baR', 'BAZ' => 'baZ']);
 
@@ -1520,13 +1528,95 @@ public function testWaitStoppedDeadProcess()
         $process->setTimeout(2);
         $process->wait();
         $this->assertFalse($process->isRunning());
+
+        if ('\\' !== \DIRECTORY_SEPARATOR && !\Closure::bind(function () { return $this->isSigchildEnabled(); }, $process, $process)()) {
+            $this->assertSame(0, $process->getExitCode());
+        }
+    }
+
+    public function testEnvCaseInsensitiveOnWindows()
+    {
+        $p = $this->getProcessForCode('print_r([$_SERVER[\'PATH\'] ?? 1, $_SERVER[\'Path\'] ?? 2]);', null, ['PATH' => 'bar/baz']);
+        $p->run(null, ['Path' => 'foo/bar']);
+
+        if ('\\' === \DIRECTORY_SEPARATOR) {
+            $this->assertSame('Array ( [0] => 1 [1] => foo/bar )', preg_replace('/\s++/', ' ', trim($p->getOutput())));
+        } else {
+            $this->assertSame('Array ( [0] => bar/baz [1] => foo/bar )', preg_replace('/\s++/', ' ', trim($p->getOutput())));
+        }
+    }
+
+    public function testMultipleCallsToProcGetStatus()
+    {
+        $process = $this->getProcess('echo foo');
+        $process->start(static function () use ($process) {
+            return $process->isRunning();
+        });
+        while ($process->isRunning()) {
+            usleep(1000);
+        }
+        $this->assertSame(0, $process->getExitCode());
+    }
+
+    public function testFailingProcessWithMultipleCallsToProcGetStatus()
+    {
+        $process = $this->getProcess('exit 123');
+        $process->start(static function () use ($process) {
+            return $process->isRunning();
+        });
+        while ($process->isRunning()) {
+            usleep(1000);
+        }
+        $this->assertSame(123, $process->getExitCode());
+    }
+
+    /**
+     * @group slow
+     */
+    public function testLongRunningProcessWithMultipleCallsToProcGetStatus()
+    {
+        $process = $this->getProcess('sleep 1 && echo "done" && php -r "exit(0);"');
+        $process->start(static function () use ($process) {
+            return $process->isRunning();
+        });
+        while ($process->isRunning()) {
+            usleep(1000);
+        }
+        $this->assertSame(0, $process->getExitCode());
+    }
+
+    /**
+     * @group slow
+     */
+    public function testLongRunningProcessWithMultipleCallsToProcGetStatusError()
+    {
+        $process = $this->getProcess('sleep 1 && echo "failure" && php -r "exit(123);"');
+        $process->start(static function () use ($process) {
+            return $process->isRunning();
+        });
+        while ($process->isRunning()) {
+            usleep(1000);
+        }
+        $this->assertSame(123, $process->getExitCode());
+    }
+
+    /**
+     * @group transient-on-windows
+     */
+    public function testNotTerminableInputPipe()
+    {
+        $process = $this->getProcess('echo foo');
+        $process->setInput(\STDIN);
+        $process->start();
+        $process->setTimeout(2);
+        $process->wait();
+        $this->assertFalse($process->isRunning());
     }
 
     /**
      * @param string|array $commandline
-     * @param mixed        $input
      */
-    private function getProcess($commandline, string $cwd = null, array $env = null, $input = null, ?int $timeout = 60): Process
+    private function getProcess($commandline, ?string $cwd = null, ?array $env = null, $input = null, ?int $timeout = 60): Process
     {
         if (\is_string($commandline)) {
             $process = Process::fromShellCommandline($commandline, $cwd, $env, $input, $timeout);
@@ -1541,7 +1631,7 @@ private function getProcess($commandline, string $cwd = null, array $env = null,
         return self::$process = $process;
     }
 
-    private function getProcessForCode(string $code, string $cwd = null, array $env = null, $input = null, ?int $timeout = 60): Process
+    private function getProcessForCode(string $code, ?string $cwd = null, ?array $env = null, $input = null, ?int $timeout = 60): Process
     {
         return $this->getProcess([self::$phpBin, '-r', $code], $cwd, $env, $input, $timeout);
     }