diff options
Diffstat (limited to 'src/corelib/thread/qsemaphore.cpp')
-rw-r--r-- | src/corelib/thread/qsemaphore.cpp | 55 |
1 files changed, 23 insertions, 32 deletions
diff --git a/src/corelib/thread/qsemaphore.cpp b/src/corelib/thread/qsemaphore.cpp index d4fb756b94..cc8099f4d4 100644 --- a/src/corelib/thread/qsemaphore.cpp +++ b/src/corelib/thread/qsemaphore.cpp @@ -354,59 +354,50 @@ void QSemaphore::release(int n) quintptr nn = unsigned(n); if (futexHasWaiterCount) nn |= quint64(nn) << 32; // token count replicated in high word - quintptr prevValue = u.fetchAndAddRelease(nn); + quintptr prevValue = u.loadRelaxed(); + quintptr newValue; + do { // loop just to ensure the operations are done atomically + newValue = prevValue + nn; + newValue &= (futexNeedsWakeAllBit - 1); + } while (!u.testAndSetRelease(prevValue, newValue, prevValue)); if (futexNeedsWake(prevValue)) { #ifdef FUTEX_OP - if (!futexHasWaiterCount) { - /* - On 32-bit systems, all waiters are waiting on the same address, - so we'll wake them all and ask the kernel to clear the high bit. - - atomic { - int oldval = u; - u = oldval & ~(1 << 31); - futexWake(u, INT_MAX); - if (oldval == 0) // impossible condition - futexWake(u, INT_MAX); - } - */ - quint32 op = FUTEX_OP_ANDN | FUTEX_OP_OPARG_SHIFT; - quint32 oparg = 31; - quint32 cmp = FUTEX_OP_CMP_EQ; - quint32 cmparg = 0; - futexWakeOp(u, INT_MAX, INT_MAX, u, FUTEX_OP(op, oparg, cmp, cmparg)); - } else { + if (futexHasWaiterCount) { /* On 64-bit systems, the single-token waiters wait on the low half and the multi-token waiters wait on the upper half. So we ask the kernel to wake up n single-token waiters and all multi-token - waiters (if any), then clear the multi-token wait bit. + waiters (if any), and clear the multi-token wait bit. atomic { int oldval = *upper; - *upper = oldval & ~(1 << 31); + *upper = oldval | 0; futexWake(lower, n); - if (oldval < 0) // sign bit set + if (oldval != 0) // always true futexWake(upper, INT_MAX); } */ - quint32 op = FUTEX_OP_ANDN | FUTEX_OP_OPARG_SHIFT; - quint32 oparg = 31; - quint32 cmp = FUTEX_OP_CMP_LT; + quint32 op = FUTEX_OP_OR; + quint32 oparg = 0; + quint32 cmp = FUTEX_OP_CMP_NE; quint32 cmparg = 0; futexWakeOp(*futexLow32(&u), n, INT_MAX, *futexHigh32(&u), FUTEX_OP(op, oparg, cmp, cmparg)); + return; } -#else - // Unset the bit and wake everyone. There are two possibibilies +#endif + // Unset the bit and wake everyone. There are two possibilities // under which a thread can set the bit between the AND and the // futexWake: // 1) it did see the new counter value, but it wasn't enough for // its acquisition anyway, so it has to wait; // 2) it did not see the new counter value, in which case its // futexWait will fail. - u.fetchAndAndRelease(futexNeedsWakeAllBit - 1); - futexWakeAll(u); -#endif + if (futexHasWaiterCount) { + futexWakeAll(*futexLow32(&u)); + futexWakeAll(*futexHigh32(&u)); + } else { + futexWakeAll(u); + } } return; } @@ -594,7 +585,7 @@ bool QSemaphore::tryAcquire(int n, int timeout) /*! \fn QSemaphoreReleaser::swap(QSemaphoreReleaser &other) - Exchanges the responsibilites of \c{*this} and \a other. + Exchanges the responsibilities of \c{*this} and \a other. Unlike move assignment, neither of the two objects ever releases its semaphore, if any, as a consequence of swapping. |