diff options
Diffstat (limited to 'pkg/sync/rwmutex_unsafe.go')
| -rw-r--r-- | pkg/sync/rwmutex_unsafe.go | 152 |
1 files changed, 124 insertions, 28 deletions
diff --git a/pkg/sync/rwmutex_unsafe.go b/pkg/sync/rwmutex_unsafe.go index b3b4dee78..4cf3fcd6e 100644 --- a/pkg/sync/rwmutex_unsafe.go +++ b/pkg/sync/rwmutex_unsafe.go @@ -3,11 +3,6 @@ // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. -// +build go1.13 -// +build !go1.17 - -// Check go:linkname function signatures when updating Go version. - // This is mostly copied from the standard library's sync/rwmutex.go. // // Happens-before relationships indicated to the race detector: @@ -23,16 +18,15 @@ import ( "unsafe" ) -//go:linkname runtimeSemacquire sync.runtime_Semacquire -func runtimeSemacquire(s *uint32) - -//go:linkname runtimeSemrelease sync.runtime_Semrelease -func runtimeSemrelease(s *uint32, handoff bool, skipframes int) - -// RWMutex is identical to sync.RWMutex, but adds the DowngradeLock, -// TryLock and TryRLock methods. -type RWMutex struct { - w Mutex // held if there are pending writers +// CrossGoroutineRWMutex is equivalent to RWMutex, but it need not be unlocked +// by a the same goroutine that locked the mutex. +type CrossGoroutineRWMutex struct { + // w is held if there are pending writers + // + // We use CrossGoroutineMutex rather than Mutex because the lock + // annotation instrumentation in Mutex will trigger false positives in + // the race detector when called inside of RaceDisable. + w CrossGoroutineMutex 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 @@ -43,7 +37,7 @@ const rwmutexMaxReaders = 1 << 30 // TryRLock locks rw for reading. It returns true if it succeeds and false // otherwise. It does not block. -func (rw *RWMutex) TryRLock() bool { +func (rw *CrossGoroutineRWMutex) TryRLock() bool { if RaceEnabled { RaceDisable() } @@ -67,13 +61,17 @@ func (rw *RWMutex) TryRLock() bool { } // RLock locks rw for reading. -func (rw *RWMutex) RLock() { +// +// 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 *CrossGoroutineRWMutex) RLock() { if RaceEnabled { RaceDisable() } if atomic.AddInt32(&rw.readerCount, 1) < 0 { // A writer is pending, wait for it. - runtimeSemacquire(&rw.readerSem) + semacquire(&rw.readerSem) } if RaceEnabled { RaceEnable() @@ -82,7 +80,10 @@ func (rw *RWMutex) RLock() { } // RUnlock undoes a single RLock call. -func (rw *RWMutex) RUnlock() { +// +// Preconditions: +// * rw is locked for reading. +func (rw *CrossGoroutineRWMutex) RUnlock() { if RaceEnabled { RaceReleaseMerge(unsafe.Pointer(&rw.writerSem)) RaceDisable() @@ -94,7 +95,7 @@ func (rw *RWMutex) RUnlock() { // A writer is pending. if atomic.AddInt32(&rw.readerWait, -1) == 0 { // The last reader unblocks the writer. - runtimeSemrelease(&rw.writerSem, false, 0) + semrelease(&rw.writerSem, false, 0) } } if RaceEnabled { @@ -104,7 +105,7 @@ func (rw *RWMutex) RUnlock() { // TryLock locks rw for writing. It returns true if it succeeds and false // otherwise. It does not block. -func (rw *RWMutex) TryLock() bool { +func (rw *CrossGoroutineRWMutex) TryLock() bool { if RaceEnabled { RaceDisable() } @@ -130,8 +131,9 @@ func (rw *RWMutex) TryLock() bool { return true } -// Lock locks rw for writing. -func (rw *RWMutex) Lock() { +// Lock locks rw for writing. If the lock is already locked for reading or +// writing, Lock blocks until the lock is available. +func (rw *CrossGoroutineRWMutex) Lock() { if RaceEnabled { RaceDisable() } @@ -141,7 +143,7 @@ func (rw *RWMutex) Lock() { r := atomic.AddInt32(&rw.readerCount, -rwmutexMaxReaders) + rwmutexMaxReaders // Wait for active readers. if r != 0 && atomic.AddInt32(&rw.readerWait, r) != 0 { - runtimeSemacquire(&rw.writerSem) + semacquire(&rw.writerSem) } if RaceEnabled { RaceEnable() @@ -150,7 +152,10 @@ func (rw *RWMutex) Lock() { } // Unlock unlocks rw for writing. -func (rw *RWMutex) Unlock() { +// +// Preconditions: +// * rw is locked for writing. +func (rw *CrossGoroutineRWMutex) Unlock() { if RaceEnabled { RaceRelease(unsafe.Pointer(&rw.writerSem)) RaceRelease(unsafe.Pointer(&rw.readerSem)) @@ -163,7 +168,7 @@ func (rw *RWMutex) Unlock() { } // Unblock blocked readers, if any. for i := 0; i < int(r); i++ { - runtimeSemrelease(&rw.readerSem, false, 0) + semrelease(&rw.readerSem, false, 0) } // Allow other writers to proceed. rw.w.Unlock() @@ -173,7 +178,10 @@ func (rw *RWMutex) Unlock() { } // DowngradeLock atomically unlocks rw for writing and locks it for reading. -func (rw *RWMutex) DowngradeLock() { +// +// Preconditions: +// * rw is locked for writing. +func (rw *CrossGoroutineRWMutex) DowngradeLock() { if RaceEnabled { RaceRelease(unsafe.Pointer(&rw.readerSem)) RaceDisable() @@ -186,7 +194,7 @@ func (rw *RWMutex) DowngradeLock() { // Unblock blocked readers, if any. Note that this loop starts as 1 since r // includes this goroutine. for i := 1; i < int(r); i++ { - runtimeSemrelease(&rw.readerSem, false, 0) + semrelease(&rw.readerSem, false, 0) } // Allow other writers to proceed to rw.w.Lock(). Note that they will still // block on rw.writerSem since at least this reader exists, such that @@ -196,3 +204,91 @@ func (rw *RWMutex) DowngradeLock() { RaceEnable() } } + +// 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. +// +// A Mutex must be unlocked by the same goroutine that locked it. This +// invariant is enforced with the 'checklocks' build tag. +type RWMutex struct { + m CrossGoroutineRWMutex +} + +// TryRLock locks rw for reading. It returns true if it succeeds and false +// otherwise. It does not block. +func (rw *RWMutex) TryRLock() bool { + // Note lock first to enforce proper locking even if unsuccessful. + noteLock(unsafe.Pointer(rw)) + locked := rw.m.TryRLock() + if !locked { + noteUnlock(unsafe.Pointer(rw)) + } + return locked +} + +// 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() { + noteLock(unsafe.Pointer(rw)) + rw.m.RLock() +} + +// RUnlock undoes a single RLock call. +// +// Preconditions: +// * rw is locked for reading. +// * rw was locked by this goroutine. +func (rw *RWMutex) RUnlock() { + rw.m.RUnlock() + noteUnlock(unsafe.Pointer(rw)) +} + +// TryLock locks rw for writing. It returns true if it succeeds and false +// otherwise. It does not block. +func (rw *RWMutex) TryLock() bool { + // Note lock first to enforce proper locking even if unsuccessful. + noteLock(unsafe.Pointer(rw)) + locked := rw.m.TryLock() + if !locked { + noteUnlock(unsafe.Pointer(rw)) + } + return locked +} + +// 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() { + noteLock(unsafe.Pointer(rw)) + rw.m.Lock() +} + +// Unlock unlocks rw for writing. +// +// Preconditions: +// * rw is locked for writing. +// * rw was locked by this goroutine. +func (rw *RWMutex) Unlock() { + rw.m.Unlock() + noteUnlock(unsafe.Pointer(rw)) +} + +// DowngradeLock atomically unlocks rw for writing and locks it for reading. +// +// Preconditions: +// * rw is locked for writing. +func (rw *RWMutex) DowngradeLock() { + // No note change for DowngradeLock. + rw.m.DowngradeLock() +} |