Make _swift_willThrow atomic (#62349)

* Make _swift_willThrow atomic

Author: grynspan

Diff for: stdlib/private/StdlibUnittest/CMakeLists.txt

@@ -46,7 +46,6 @@ add_swift_target_library(swiftStdlibUnittest ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES}
   StdlibCoreExtras.swift
   StringConvertible.swift
   StringTestHelpers.swift
-  SymbolLookup.swift
   TestHelpers.swift
   TypeIndexed.swift
 

Diff for: stdlib/private/StdlibUnittest/SymbolLookup.swift

@@ -24,15 +24,20 @@
 
 using namespace swift;
 
-void (*swift::_swift_willThrow)(SwiftError *error);
+std::atomic<void (*)(SwiftError *error)> swift::_swift_willThrow;
+
+void swift::_swift_setWillThrowHandler(void (* handler)(SwiftError *error)) {
+  _swift_willThrow.store(handler, std::memory_order_release);
+}
 
 /// Breakpoint hook for debuggers, and calls _swift_willThrow if set.
 SWIFT_CC(swift) void
 swift::swift_willThrow(SWIFT_CONTEXT void *unused,
                        SWIFT_ERROR_RESULT SwiftError **error) {
   // Cheap check to bail out early, since we expect there to be no callbacks
   // the vast majority of the time.
-  if (SWIFT_LIKELY(!_swift_willThrow))
-    return;
-  _swift_willThrow(*error);
+  auto handler = _swift_willThrow.load(std::memory_order_acquire);
+  if (SWIFT_UNLIKELY(handler)) {
+    (* handler)(*error);
+  }
 }

Diff for: stdlib/public/runtime/ErrorObjectCommon.cpp

@@ -17,10 +17,20 @@
 #ifndef SWIFT_RUNTIME_ERROROBJECT_TEST_SUPPORT_H
 #define SWIFT_RUNTIME_ERROROBJECT_TEST_SUPPORT_H
 
+#include <atomic>
+
 namespace swift {
 
-SWIFT_RUNTIME_EXPORT void (*_swift_willThrow)(SwiftError *error);
+#if defined(__cplusplus)
+SWIFT_RUNTIME_EXPORT std::atomic<void (*)(SwiftError *error)> _swift_willThrow;
+#endif
 
+/// Set the value of @c _swift_willThrow atomically.
+///
+/// This function is present for use by the standard library's test suite only.
+SWIFT_CC(swift)
+SWIFT_RUNTIME_STDLIB_SPI
+void _swift_setWillThrowHandler(void (* handler)(SwiftError *error));
 }
 
 #endif

Diff for: stdlib/public/runtime/ErrorObjectTestSupport.h

@@ -219,28 +219,35 @@ func throwJazzHands() throws {
   throw SillyError.JazzHands
 }
 
-ErrorTests.test("willThrow") {
-  if #available(SwiftStdlib 5.2, *) {
-    // Error isn't allowed in a @convention(c) function when ObjC interop is
-    // not available, so pass it through an OpaquePointer.
-    typealias WillThrow = @convention(c) (OpaquePointer) -> Void
-    let willThrow = pointerToSwiftCoreSymbol(name: "_swift_willThrow")!
-    let callback: WillThrow = {
-      errors.append(unsafeBitCast($0, to: Error.self))
-    }
-    willThrow.storeBytes(of: callback, as: WillThrow.self)
-    expectTrue(errors.isEmpty)
-    do {
-      try throwNegativeOne()
-    } catch {}
-    expectEqual(UnsignedError.self, type(of: errors.last!))
+// Error isn't allowed in a @convention(c) function when ObjC interop is
+// not available, so pass it through an UnsafeRawPointer.
+@available(SwiftStdlib 5.8, *)
+@_silgen_name("_swift_setWillThrowHandler")
+func setWillThrowHandler(
+    _ handler: (@convention(c) (UnsafeRawPointer) -> Void)?
+)
 
-    do {
-      try throwJazzHands()
-    } catch {}
-    expectEqual(2, errors.count)
-    expectEqual(SillyError.self, type(of: errors.last!))
+ErrorTests.test("willThrow") {
+  guard #available(SwiftStdlib 5.8, *) else {
+    return
   }
+  setWillThrowHandler {
+    errors.append(unsafeBitCast($0, to: Error.self))
+  }
+  defer {
+    setWillThrowHandler(nil)
+  }
+  expectTrue(errors.isEmpty)
+  do {
+    try throwNegativeOne()
+  } catch {}
+  expectEqual(UnsignedError.self, type(of: errors.last!))
+
+  do {
+    try throwJazzHands()
+  } catch {}
+  expectEqual(2, errors.count)
+  expectEqual(SillyError.self, type(of: errors.last!))
 }
 
 runAllTests()