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MDEV-24167 fixup: Avoid hangs in SRW_LOCK_DUMMY

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In commit 1fdc161d8f we introduced
a mutex-and-condition-variable based fallback implementation
for platforms that lack a futex system call. That implementation
is prone to hangs.

Let us use separate condition variables for shared and exclusive requests.
This commit is contained in:
Marko Mäkelä 2020-12-03 09:11:31 +02:00
commit 260161fc9f
2 changed files with 45 additions and 25 deletions
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12
storage/innobase/include/srw_lock.h
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@ -35,7 +35,8 @@ class srw_lock_low final : private rw_lock
#endif
#ifdef SRW_LOCK_DUMMY
pthread_mutex_t mutex;
pthread_cond_t cond;
pthread_cond_t cond_shared;
pthread_cond_t cond_exclusive;
#endif
/** @return pointer to the lock word */
rw_lock *word() { return static_cast<rw_lock*>(this); }
@ -46,11 +47,14 @@ class srw_lock_low final : private rw_lock
void write_lock();
/** Wait for signal
@param l lock word from a failed acquisition */
inline void wait(uint32_t l);
inline void writer_wait(uint32_t l);
/** Wait for signal
@param l lock word from a failed acquisition */
inline void readers_wait(uint32_t l);
/** Send signal to one waiter */
inline void wake_one();
inline void writer_wake();
/** Send signal to all waiters */
inline void wake_all();
inline void readers_wake();
public:
#ifdef SRW_LOCK_DUMMY
void init();