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contenting mutex #992

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9 changes: 7 additions & 2 deletions thread/thread.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1721,7 +1721,7 @@ R"(
{
assert(h->waitq == (thread_list*)this);
prelocked_thread_interrupt(h, error_number);
assert(h->waitq == nullptr);
// assert(h->waitq == nullptr);
assert(this->q.th != h);
}
return h;
Expand All @@ -1746,6 +1746,7 @@ R"(
if (unlikely(ret)) { errno = ret; return -1; }
if (try_lock() == 0) return 0;
}
again:
splock.lock();
if (try_lock() == 0) {
splock.unlock();
Expand All @@ -1760,6 +1761,10 @@ R"(

int ret = thread_usleep_defer(timeout,
(thread_list*)&q, &spinlock_unlock, &splock);
if (likely(ret < 0 && errno == -1)) {
auto o = owner.load(std::memory_order_acquire);
if (unlikely(o != CURRENT)) { assert(_contending); goto again; }
}
return waitq_translate_errno(ret);
}
int mutex::try_lock()
Expand All @@ -1773,7 +1778,7 @@ R"(
{
SCOPED_LOCK(m->splock);
ScopedLockHead h(m);
m->owner.store(h);
m->owner.store(unlikely(m->_contending) ? nullptr : (thread*)h);
if (h)
prelocked_thread_interrupt(h, -1);
}
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4 changes: 3 additions & 1 deletion thread/thread.h
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Original file line number Diff line number Diff line change
Expand Up @@ -284,7 +284,8 @@ namespace photon
class mutex : protected waitq
{
public:
mutex(uint16_t max_retries = 100) : retries(max_retries) { }
mutex(uint16_t max_retries = 100, bool contending = false)
: retries(max_retries), _contending(contending) { }
int lock(Timeout timeout = {});
int try_lock();
void unlock();
Expand All @@ -297,6 +298,7 @@ namespace photon
std::atomic<thread*> owner{nullptr};
uint16_t retries;
spinlock splock;
bool _contending;
};

class seq_mutex : protected mutex {
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