diff --git a/pkg/sync/downgradable_rwmutex_unsafe.go b/pkg/sync/downgradable_rwmutex_unsafe.go index 9bb55cd3a..0d321f5e3 100755 --- a/pkg/sync/downgradable_rwmutex_unsafe.go +++ b/pkg/sync/downgradable_rwmutex_unsafe.go @@ -19,7 +19,6 @@ package sync import ( - "sync" "sync/atomic" "unsafe" ) @@ -30,18 +29,43 @@ func runtimeSemacquire(s *uint32) //go:linkname runtimeSemrelease sync.runtime_Semrelease func runtimeSemrelease(s *uint32, handoff bool, skipframes int) -// DowngradableRWMutex is identical to sync.RWMutex, but adds the DowngradeLock -// method. +// DowngradableRWMutex is identical to sync.RWMutex, but adds the DowngradeLock, +// TryLock and TryRLock methods. type DowngradableRWMutex struct { - w sync.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 + w TMutex // 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 +// TryRLock locks rw for reading. It returns true if it succeeds and false +// otherwise. It does not block. +func (rw *DowngradableRWMutex) TryRLock() bool { + if RaceEnabled { + RaceDisable() + } + for { + rc := atomic.LoadInt32(&rw.readerCount) + if rc < 0 { + if RaceEnabled { + RaceEnable() + } + return false + } + if !atomic.CompareAndSwapInt32(&rw.readerCount, rc, rc+1) { + continue + } + if RaceEnabled { + RaceEnable() + RaceAcquire(unsafe.Pointer(&rw.readerSem)) + } + return true + } +} + // RLock locks rw for reading. func (rw *DowngradableRWMutex) RLock() { if RaceEnabled { @@ -78,6 +102,34 @@ func (rw *DowngradableRWMutex) RUnlock() { } } +// TryLock locks rw for writing. It returns true if it succeeds and false +// otherwise. It does not block. +func (rw *DowngradableRWMutex) TryLock() bool { + if RaceEnabled { + RaceDisable() + } + // First, resolve competition with other writers. + if !rw.w.TryLock() { + if RaceEnabled { + RaceEnable() + } + return false + } + // Only proceed if there are no readers. + if !atomic.CompareAndSwapInt32(&rw.readerCount, 0, -rwmutexMaxReaders) { + rw.w.Unlock() + if RaceEnabled { + RaceEnable() + } + return false + } + if RaceEnabled { + RaceEnable() + RaceAcquire(unsafe.Pointer(&rw.writerSem)) + } + return true +} + // Lock locks rw for writing. func (rw *DowngradableRWMutex) Lock() { if RaceEnabled {