diff options
Diffstat (limited to 'src/runtime/rwmutex.go')
| -rw-r--r-- | src/runtime/rwmutex.go | 30 |
1 files changed, 17 insertions, 13 deletions
diff --git a/src/runtime/rwmutex.go b/src/runtime/rwmutex.go index 89fe16c10d..34d8f675c1 100644 --- a/src/runtime/rwmutex.go +++ b/src/runtime/rwmutex.go @@ -27,7 +27,6 @@ type rwmutex struct { readerWait atomic.Int32 // number of departing readers readRank lockRank // semantic lock rank for read locking - writeRank lockRank // semantic lock rank for write locking } // Lock ranking an rwmutex has two aspects: @@ -41,21 +40,28 @@ type rwmutex struct { // rLock and wLock. These have lock order requirements: wLock must be locked // before rLock. This also needs to be represented in the lock rank. // -// Internal ranking is represented by assigning ranks rwmutexR and rwmutexW to -// rLock and wLock, respectively. -// // Semantic ranking is represented by acquiring readRank during read lock and // writeRank during write lock. // -// readRank is always taken before rwmutexR and writeRank is always taken -// before rwmutexW, so each unique rwmutex must record this order in the lock -// ranking. -func (rw *rwmutex) init(readRank, writeRank lockRank) { +// wLock is held for the duration of a write lock, so it uses writeRank +// directly, both for semantic and internal ranking. rLock is only held +// temporarily inside the rlock/lock methods, so it uses readRankInternal to +// represent internal ranking. Semantic ranking is represented by a separate +// acquire of readRank for the duration of a read lock. +// +// The lock ranking must document this ordering: +// - readRankInternal is a leaf lock. +// - readRank is taken before readRankInternal. +// - writeRank is taken before readRankInternal. +// - readRank is placed in the lock order wherever a read lock of this rwmutex +// belongs. +// - writeRank is placed in the lock order wherever a write lock of this +// rwmutex belongs. +func (rw *rwmutex) init(readRank, readRankInternal, writeRank lockRank) { rw.readRank = readRank - rw.writeRank = writeRank - lockInit(&rw.rLock, lockRankRwmutexR) - lockInit(&rw.wLock, lockRankRwmutexW) + lockInit(&rw.rLock, readRankInternal) + lockInit(&rw.wLock, writeRank) } const rwmutexMaxReaders = 1 << 30 @@ -117,7 +123,6 @@ func (rw *rwmutex) runlock() { // lock locks rw for writing. func (rw *rwmutex) lock() { // Resolve competition with other writers and stick to our P. - acquireLockRank(rw.writeRank) lock(&rw.wLock) m := getg().m // Announce that there is a pending writer. @@ -159,5 +164,4 @@ func (rw *rwmutex) unlock() { unlock(&rw.rLock) // Allow other writers to proceed. unlock(&rw.wLock) - releaseLockRank(rw.writeRank) } |