CancelWait cancels effects of the previous Prewait call.
| 109 | |
| 110 | // CancelWait cancels effects of the previous Prewait call. |
| 111 | void CancelWait() { |
| 112 | uint64_t state = state_.load(std::memory_order_relaxed); |
| 113 | for (;;) { |
| 114 | CheckState(state, true); |
| 115 | uint64_t newstate = state - kWaiterInc; |
| 116 | // We don't know if the thread was also notified or not, |
| 117 | // so we should not consume a signal unconditionally. |
| 118 | // Only if number of waiters is equal to number of signals, |
| 119 | // we know that the thread was notified and we must take away the signal. |
| 120 | if (((state & kWaiterMask) >> kWaiterShift) == |
| 121 | ((state & kSignalMask) >> kSignalShift)) |
| 122 | newstate -= kSignalInc; |
| 123 | CheckState(newstate); |
| 124 | if (state_.compare_exchange_weak(state, newstate, |
| 125 | std::memory_order_acq_rel)) |
| 126 | return; |
| 127 | } |
| 128 | } |
| 129 | |
| 130 | // Notify wakes one or all waiting threads. |
| 131 | // Must be called after changing the associated wait predicate. |