diff options
author | Ian Gudger <igudger@google.com> | 2020-01-21 18:34:24 -0800 |
---|---|---|
committer | gVisor bot <gvisor-bot@google.com> | 2020-01-21 19:11:18 -0800 |
commit | d0e75f2bef4e16356693987db6ae6bbdce749618 (patch) | |
tree | 519ba9b2251b143b0115b2ae31d5c904e11b23f8 /pkg | |
parent | 1effdc091b441c4b1ada4327c1422cd360f80f98 (diff) |
Add trylock support to DowngradableRWMutex.
Updates #231
PiperOrigin-RevId: 290868875
Diffstat (limited to 'pkg')
-rw-r--r-- | pkg/sync/downgradable_rwmutex_test.go | 55 | ||||
-rw-r--r-- | pkg/sync/downgradable_rwmutex_unsafe.go | 68 |
2 files changed, 115 insertions, 8 deletions
diff --git a/pkg/sync/downgradable_rwmutex_test.go b/pkg/sync/downgradable_rwmutex_test.go index f04496bc5..b5cb28ec0 100644 --- a/pkg/sync/downgradable_rwmutex_test.go +++ b/pkg/sync/downgradable_rwmutex_test.go @@ -148,3 +148,58 @@ func TestDowngradableRWMutex(t *testing.T) { HammerDowngradableRWMutex(10, 10, n) HammerDowngradableRWMutex(10, 5, n) } + +func TestRWDoubleTryLock(t *testing.T) { + var m DowngradableRWMutex + if !m.TryLock() { + t.Fatal("failed to aquire lock") + } + if m.TryLock() { + t.Fatal("unexpectedly succeeded in aquiring locked mutex") + } +} + +func TestRWTryLockAfterLock(t *testing.T) { + var m DowngradableRWMutex + m.Lock() + if m.TryLock() { + t.Fatal("unexpectedly succeeded in aquiring locked mutex") + } +} + +func TestRWTryLockUnlock(t *testing.T) { + var m DowngradableRWMutex + if !m.TryLock() { + t.Fatal("failed to aquire lock") + } + m.Unlock() + if !m.TryLock() { + t.Fatal("failed to aquire lock after unlock") + } +} + +func TestTryRLockAfterLock(t *testing.T) { + var m DowngradableRWMutex + m.Lock() + if m.TryRLock() { + t.Fatal("unexpectedly succeeded in aquiring locked mutex") + } +} + +func TestTryLockAfterRLock(t *testing.T) { + var m DowngradableRWMutex + m.RLock() + if m.TryLock() { + t.Fatal("unexpectedly succeeded in aquiring locked mutex") + } +} + +func TestDoubleTryRLock(t *testing.T) { + var m DowngradableRWMutex + if !m.TryRLock() { + t.Fatal("failed to aquire lock") + } + if !m.TryRLock() { + t.Fatal("failed to read aquire read locked lock") + } +} diff --git a/pkg/sync/downgradable_rwmutex_unsafe.go b/pkg/sync/downgradable_rwmutex_unsafe.go index 9bb55cd3a..0d321f5e3 100644 --- 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 { |