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optimize lock_shared

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This commit is contained in:
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() {
auto old = lc_.load(std::memory_order_relaxed);
for (unsigned k = 0;; ++k) {
auto old = lc_.load(std::memory_order_relaxed);
// if w_flag set, just continue; otherwise cas lc + 1 (set r-lock)
if (!(old & w_flag) &&
lc_.compare_exchange_weak(old, old + 1, std::memory_order_acquire)) {
// if w_flag set, just continue
if (old & w_flag) {
yield(k);
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;
}
yield(k);
std::atomic_thread_fence(std::memory_order_acquire);
// set r-lock failed, old has been updated
}
}