diff options
author | Benjamin Barenblat <bbaren@google.com> | 2021-04-08 10:23:55 -0400 |
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committer | Benjamin Barenblat <bbaren@google.com> | 2021-04-08 10:23:55 -0400 |
commit | feac56827dd1f0d159ea0bcf2ce37ef1990ac743 (patch) | |
tree | bc8ca767be02a5b22118108f9712b72ec64064c3 /absl/base/internal/spinlock.cc | |
parent | 2b91b17d526b464840a3f45504c594cdb50152c5 (diff) | |
parent | 997aaf3a28308eba1b9156aa35ab7bca9688e9f6 (diff) |
Merge new upstream LTS 20210324.0
Diffstat (limited to 'absl/base/internal/spinlock.cc')
-rw-r--r-- | absl/base/internal/spinlock.cc | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/absl/base/internal/spinlock.cc b/absl/base/internal/spinlock.cc index a7d44f3e..35c0696a 100644 --- a/absl/base/internal/spinlock.cc +++ b/absl/base/internal/spinlock.cc @@ -125,8 +125,9 @@ void SpinLock::SlowLock() { // it as having a sleeper. if ((lock_value & kWaitTimeMask) == 0) { // Here, just "mark" that the thread is going to sleep. Don't store the - // lock wait time in the lock as that will cause the current lock - // owner to think it experienced contention. + // lock wait time in the lock -- the lock word stores the amount of time + // that the current holder waited before acquiring the lock, not the wait + // time of any thread currently waiting to acquire it. if (lockword_.compare_exchange_strong( lock_value, lock_value | kSpinLockSleeper, std::memory_order_relaxed, std::memory_order_relaxed)) { @@ -140,6 +141,14 @@ void SpinLock::SlowLock() { // this thread obtains the lock. lock_value = TryLockInternal(lock_value, wait_cycles); continue; // Skip the delay at the end of the loop. + } else if ((lock_value & kWaitTimeMask) == 0) { + // The lock is still held, without a waiter being marked, but something + // else about the lock word changed, causing our CAS to fail. For + // example, a new lock holder may have acquired the lock with + // kSpinLockDisabledScheduling set, whereas the previous holder had not + // set that flag. In this case, attempt again to mark ourselves as a + // waiter. + continue; } } |