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optimize lock_shared

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mutouyun 2018-12-14 11:21:46 +08:00
parent 238f769f7a
commit 7b812c3c6e
1 changed files with 9 additions and 6 deletions
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15
include/rw_lock.h
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@ -36,15 +36,18 @@ public:
} }
void lock_shared() { void lock_shared() {
auto old = lc_.load(std::memory_order_relaxed);
for (unsigned k = 0;; ++k) { for (unsigned k = 0;; ++k) {
auto old = lc_.load(std::memory_order_relaxed); // if w_flag set, just continue
// if w_flag set, just continue; otherwise cas lc + 1 (set r-lock) if (old & w_flag) {
if (!(old & w_flag) && yield(k);
lc_.compare_exchange_weak(old, old + 1, std::memory_order_acquire)) { old = lc_.load(std::memory_order_acquire);
}
// otherwise try cas lc + 1 (set r-lock)
else if (lc_.compare_exchange_weak(old, old + 1, std::memory_order_acquire)) {
break; break;
} }
yield(k); // set r-lock failed, old has been updated
std::atomic_thread_fence(std::memory_order_acquire);
} }
} }