add 1.13 file

Author: cch123

1.13/memory.md

@@ -0,0 +1,105 @@
+// There is a modified copy of this file in runtime/rwmutex.go.
+// If you make any changes here, see if you should make them there.
+
+// A RWMutex is a reader/writer mutual exclusion lock.
+// The lock can be held by an arbitrary number of readers or a single writer.
+// The zero value for a RWMutex is an unlocked mutex.
+//
+// A RWMutex must not be copied after first use.
+//
+// If a goroutine holds a RWMutex for reading and another goroutine might
+// call Lock, no goroutine should expect to be able to acquire a read lock
+// until the initial read lock is released. In particular, this prohibits
+// recursive read locking. This is to ensure that the lock eventually becomes
+// available; a blocked Lock call excludes new readers from acquiring the
+// lock.
+type RWMutex struct {
+	w           Mutex  // held if there are pending writers
+	writerSem   uint32 // semaphore for writers to wait for completing readers
+	readerSem   uint32 // semaphore for readers to wait for completing writers
+	readerCount int32  // number of pending readers
+	readerWait  int32  // number of departing readers
+}
+
+const rwmutexMaxReaders = 1 << 30
+
+// RLock locks rw for reading.
+//
+// It should not be used for recursive read locking; a blocked Lock
+// call excludes new readers from acquiring the lock. See the
+// documentation on the RWMutex type.
+func (rw *RWMutex) RLock() {
+	if atomic.AddInt32(&rw.readerCount, 1) < 0 {
+		// A writer is pending, wait for it.
+		runtime_SemacquireMutex(&rw.readerSem, false, 0)
+	}
+}
+
+// RUnlock undoes a single RLock call;
+// it does not affect other simultaneous readers.
+// It is a run-time error if rw is not locked for reading
+// on entry to RUnlock.
+func (rw *RWMutex) RUnlock() {
+	if r := atomic.AddInt32(&rw.readerCount, -1); r < 0 {
+		// Outlined slow-path to allow the fast-path to be inlined
+		rw.rUnlockSlow(r)
+	}
+}
+
+func (rw *RWMutex) rUnlockSlow(r int32) {
+	if r+1 == 0 || r+1 == -rwmutexMaxReaders {
+		throw("sync: RUnlock of unlocked RWMutex")
+	}
+	// A writer is pending.
+	if atomic.AddInt32(&rw.readerWait, -1) == 0 {
+		// The last reader unblocks the writer.
+		runtime_Semrelease(&rw.writerSem, false, 1)
+	}
+}
+
+// Lock locks rw for writing.
+// If the lock is already locked for reading or writing,
+// Lock blocks until the lock is available.
+func (rw *RWMutex) Lock() {
+	// First, resolve competition with other writers.
+	rw.w.Lock()
+	// Announce to readers there is a pending writer.
+	r := atomic.AddInt32(&rw.readerCount, -rwmutexMaxReaders) + rwmutexMaxReaders
+	// Wait for active readers.
+	if r != 0 && atomic.AddInt32(&rw.readerWait, r) != 0 {
+		runtime_SemacquireMutex(&rw.writerSem, false, 0)
+	}
+}
+
+// Unlock unlocks rw for writing. It is a run-time error if rw is
+// not locked for writing on entry to Unlock.
+//
+// As with Mutexes, a locked RWMutex is not associated with a particular
+// goroutine. One goroutine may RLock (Lock) a RWMutex and then
+// arrange for another goroutine to RUnlock (Unlock) it.
+func (rw *RWMutex) Unlock() {
+
+	// Announce to readers there is no active writer.
+	r := atomic.AddInt32(&rw.readerCount, rwmutexMaxReaders)
+	if r >= rwmutexMaxReaders {
+		throw("sync: Unlock of unlocked RWMutex")
+	}
+	// Unblock blocked readers, if any.
+	for i := 0; i < int(r); i++ {
+		runtime_Semrelease(&rw.readerSem, false, 0)
+	}
+	// Allow other writers to proceed.
+	rw.w.Unlock()
+}
+
+// RLocker returns a Locker interface that implements
+// the Lock and Unlock methods by calling rw.RLock and rw.RUnlock.
+func (rw *RWMutex) RLocker() Locker {
+	return (*rlocker)(rw)
+}
+
+type rlocker RWMutex
+
+func (r *rlocker) Lock()   { (*RWMutex)(r).RLock() }
+func (r *rlocker) Unlock() { (*RWMutex)(r).RUnlock() }
+

1.13/rwmutex.md

@@ -0,0 +1,254 @@
+// A Pool is a set of temporary objects that may be individually saved and
+// retrieved.
+//
+// Any item stored in the Pool may be removed automatically at any time without
+// notification. If the Pool holds the only reference when this happens, the
+// item might be deallocated.
+//
+// A Pool is safe for use by multiple goroutines simultaneously.
+//
+// Pool's purpose is to cache allocated but unused items for later reuse,
+// relieving pressure on the garbage collector. That is, it makes it easy to
+// build efficient, thread-safe free lists. However, it is not suitable for all
+// free lists.
+//
+// An appropriate use of a Pool is to manage a group of temporary items
+// silently shared among and potentially reused by concurrent independent
+// clients of a package. Pool provides a way to amortize allocation overhead
+// across many clients.
+//
+// An example of good use of a Pool is in the fmt package, which maintains a
+// dynamically-sized store of temporary output buffers. The store scales under
+// load (when many goroutines are actively printing) and shrinks when
+// quiescent.
+//
+// On the other hand, a free list maintained as part of a short-lived object is
+// not a suitable use for a Pool, since the overhead does not amortize well in
+// that scenario. It is more efficient to have such objects implement their own
+// free list.
+//
+// A Pool must not be copied after first use.
+type Pool struct {
+	noCopy noCopy
+
+	local     unsafe.Pointer // local fixed-size per-P pool, actual type is [P]poolLocal
+	localSize uintptr        // size of the local array
+
+	victim     unsafe.Pointer // local from previous cycle
+	victimSize uintptr        // size of victims array
+
+	// New optionally specifies a function to generate
+	// a value when Get would otherwise return nil.
+	// It may not be changed concurrently with calls to Get.
+	New func() interface{}
+}
+
+// Local per-P Pool appendix.
+type poolLocalInternal struct {
+	private interface{} // Can be used only by the respective P.
+	shared  poolChain   // Local P can pushHead/popHead; any P can popTail.
+}
+
+type poolLocal struct {
+	poolLocalInternal
+
+	// Prevents false sharing on widespread platforms with
+	// 128 mod (cache line size) = 0 .
+	pad [128 - unsafe.Sizeof(poolLocalInternal{})%128]byte
+}
+
+// from runtime
+func fastrand() uint32
+
+var poolRaceHash [128]uint64
+
+// poolRaceAddr returns an address to use as the synchronization point
+// for race detector logic. We don't use the actual pointer stored in x
+// directly, for fear of conflicting with other synchronization on that address.
+// Instead, we hash the pointer to get an index into poolRaceHash.
+// See discussion on golang.org/cl/31589.
+func poolRaceAddr(x interface{}) unsafe.Pointer {
+	ptr := uintptr((*[2]unsafe.Pointer)(unsafe.Pointer(&x))[1])
+	h := uint32((uint64(uint32(ptr)) * 0x85ebca6b) >> 16)
+	return unsafe.Pointer(&poolRaceHash[h%uint32(len(poolRaceHash))])
+}
+
+// Put adds x to the pool.
+func (p *Pool) Put(x interface{}) {
+	if x == nil {
+		return
+	}
+
+	l, _ := p.pin()
+	if l.private == nil {
+		l.private = x
+		x = nil
+	}
+	if x != nil {
+		l.shared.pushHead(x)
+	}
+	runtime_procUnpin()
+}
+
+// Get selects an arbitrary item from the Pool, removes it from the
+// Pool, and returns it to the caller.
+// Get may choose to ignore the pool and treat it as empty.
+// Callers should not assume any relation between values passed to Put and
+// the values returned by Get.
+//
+// If Get would otherwise return nil and p.New is non-nil, Get returns
+// the result of calling p.New.
+func (p *Pool) Get() interface{} {
+	l, pid := p.pin()
+	x := l.private
+	l.private = nil
+	if x == nil {
+		// Try to pop the head of the local shard. We prefer
+		// the head over the tail for temporal locality of
+		// reuse.
+		x, _ = l.shared.popHead()
+		if x == nil {
+			x = p.getSlow(pid)
+		}
+	}
+	runtime_procUnpin()
+
+	if x == nil && p.New != nil {
+		x = p.New()
+	}
+	return x
+}
+
+func (p *Pool) getSlow(pid int) interface{} {
+	// See the comment in pin regarding ordering of the loads.
+	size := atomic.LoadUintptr(&p.localSize) // load-acquire
+	locals := p.local                        // load-consume
+	// Try to steal one element from other procs.
+	for i := 0; i < int(size); i++ {
+		l := indexLocal(locals, (pid+i+1)%int(size))
+		if x, _ := l.shared.popTail(); x != nil {
+			return x
+		}
+	}
+
+	// Try the victim cache. We do this after attempting to steal
+	// from all primary caches because we want objects in the
+	// victim cache to age out if at all possible.
+	size = atomic.LoadUintptr(&p.victimSize)
+	if uintptr(pid) >= size {
+		return nil
+	}
+	locals = p.victim
+	l := indexLocal(locals, pid)
+	if x := l.private; x != nil {
+		l.private = nil
+		return x
+	}
+	for i := 0; i < int(size); i++ {
+		l := indexLocal(locals, (pid+i)%int(size))
+		if x, _ := l.shared.popTail(); x != nil {
+			return x
+		}
+	}
+
+	// Mark the victim cache as empty for future gets don't bother
+	// with it.
+	atomic.StoreUintptr(&p.victimSize, 0)
+
+	return nil
+}
+
+// pin pins the current goroutine to P, disables preemption and
+// returns poolLocal pool for the P and the P's id.
+// Caller must call runtime_procUnpin() when done with the pool.
+func (p *Pool) pin() (*poolLocal, int) {
+	pid := runtime_procPin()
+	// In pinSlow we store to local and then to localSize, here we load in opposite order.
+	// Since we've disabled preemption, GC cannot happen in between.
+	// Thus here we must observe local at least as large localSize.
+	// We can observe a newer/larger local, it is fine (we must observe its zero-initialized-ness).
+	s := atomic.LoadUintptr(&p.localSize) // load-acquire
+	l := p.local                          // load-consume
+	if uintptr(pid) < s {
+		return indexLocal(l, pid), pid
+	}
+	return p.pinSlow()
+}
+
+func (p *Pool) pinSlow() (*poolLocal, int) {
+	// Retry under the mutex.
+	// Can not lock the mutex while pinned.
+	runtime_procUnpin()
+	allPoolsMu.Lock()
+	defer allPoolsMu.Unlock()
+	pid := runtime_procPin()
+	// poolCleanup won't be called while we are pinned.
+	s := p.localSize
+	l := p.local
+	if uintptr(pid) < s {
+		return indexLocal(l, pid), pid
+	}
+	if p.local == nil {
+		allPools = append(allPools, p)
+	}
+	// If GOMAXPROCS changes between GCs, we re-allocate the array and lose the old one.
+	size := runtime.GOMAXPROCS(0)
+	local := make([]poolLocal, size)
+	atomic.StorePointer(&p.local, unsafe.Pointer(&local[0])) // store-release
+	atomic.StoreUintptr(&p.localSize, uintptr(size))         // store-release
+	return &local[pid], pid
+}
+
+func poolCleanup() {
+	// This function is called with the world stopped, at the beginning of a garbage collection.
+	// It must not allocate and probably should not call any runtime functions.
+
+	// Because the world is stopped, no pool user can be in a
+	// pinned section (in effect, this has all Ps pinned).
+
+	// Drop victim caches from all pools.
+	for _, p := range oldPools {
+		p.victim = nil
+		p.victimSize = 0
+	}
+
+	// Move primary cache to victim cache.
+	for _, p := range allPools {
+		p.victim = p.local
+		p.victimSize = p.localSize
+		p.local = nil
+		p.localSize = 0
+	}
+
+	// The pools with non-empty primary caches now have non-empty
+	// victim caches and no pools have primary caches.
+	oldPools, allPools = allPools, nil
+}
+
+var (
+	allPoolsMu Mutex
+
+	// allPools is the set of pools that have non-empty primary
+	// caches. Protected by either 1) allPoolsMu and pinning or 2)
+	// STW.
+	allPools []*Pool
+
+	// oldPools is the set of pools that may have non-empty victim
+	// caches. Protected by STW.
+	oldPools []*Pool
+)
+
+func init() {
+	runtime_registerPoolCleanup(poolCleanup)
+}
+
+func indexLocal(l unsafe.Pointer, i int) *poolLocal {
+	lp := unsafe.Pointer(uintptr(l) + uintptr(i)*unsafe.Sizeof(poolLocal{}))
+	return (*poolLocal)(lp)
+}
+
+// Implemented in runtime.
+func runtime_registerPoolCleanup(cleanup func())
+func runtime_procPin() int
+func runtime_procUnpin()
+