Commit 6b2d1766 authored by Marko Mäkelä's avatar Marko Mäkelä

MDEV-24167 fixup: Avoid hangs in SRW_LOCK_DUMMY

In commit 1fdc161d 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 write and read requests.
parent c152f595
......@@ -52,6 +52,7 @@ class srw_lock_low final : private rw_lock
#ifdef SRW_LOCK_DUMMY
pthread_mutex_t mutex;
pthread_cond_t cond;
pthread_cond_t cond_ex;
#endif
/** @return pointer to the lock word */
rw_lock *word() { return static_cast<rw_lock*>(this); }
......@@ -66,11 +67,14 @@ class srw_lock_low final : private rw_lock
void write_lock(bool holding_u);
/** 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();
......
......@@ -25,6 +25,7 @@ void srw_lock_low::init()
DBUG_ASSERT(!is_locked_or_waiting());
pthread_mutex_init(&mutex, nullptr);
pthread_cond_init(&cond, nullptr);
pthread_cond_init(&cond_ex, nullptr);
}
void srw_lock_low::destroy()
......@@ -32,40 +33,58 @@ void srw_lock_low::destroy()
DBUG_ASSERT(!is_locked_or_waiting());
pthread_mutex_destroy(&mutex);
pthread_cond_destroy(&cond);
pthread_cond_destroy(&cond_ex);
}
inline void srw_lock_low::wait(uint32_t l)
inline void srw_lock_low::writer_wait(uint32_t l)
{
pthread_mutex_lock(&mutex);
if (value() == l)
pthread_cond_wait(&cond, &mutex);
pthread_cond_wait(&cond_ex, &mutex);
pthread_mutex_unlock(&mutex);
}
inline void srw_lock_low::wake_one()
inline void srw_lock_low::readers_wait(uint32_t l)
{
pthread_mutex_lock(&mutex);
pthread_cond_signal(&cond);
if (value() == l)
pthread_cond_wait(&cond, &mutex);
pthread_mutex_unlock(&mutex);
}
inline void srw_lock_low::wake_all()
#if 0
inline void srw_lock_low::writer_wake()
{
pthread_mutex_lock(&mutex);
pthread_cond_broadcast(&cond_ex);
if (!(value() & WRITER_PENDING))
pthread_cond_broadcast(&cond);
pthread_mutex_unlock(&mutex);
}
#endif
inline void srw_lock_low::writer_wake()
{
pthread_mutex_lock(&mutex);
uint32_t l= value();
if (!(l & WRITER))
pthread_cond_broadcast((l & WRITER_PENDING) ? &cond_ex : &cond);
else
DBUG_ASSERT(!(l & ~WRITER_PENDING));
pthread_mutex_unlock(&mutex);
}
# define readers_wake writer_wake
#else
static_assert(4 == sizeof(rw_lock), "ABI");
# ifdef _WIN32
# include <synchapi.h>
inline void srw_lock_low::wait(uint32_t l)
inline void srw_lock_low::writer_wait(uint32_t l)
{
WaitOnAddress(word(), &l, 4, INFINITE);
}
inline void srw_lock_low::wake_one() { WakeByAddressSingle(word()); }
inline void srw_lock_low::wake_all() { WakeByAddressAll(word()); }
inline void srw_lock_low::writer_wake() { WakeByAddressSingle(word()); }
inline void srw_lock_low::readers_wake() { WakeByAddressAll(word()); }
# else
# ifdef __linux__
# include <linux/futex.h>
......@@ -81,10 +100,14 @@ inline void srw_lock_low::wake_all() { WakeByAddressAll(word()); }
# error "no futex support"
# endif
inline void srw_lock_low::wait(uint32_t l) { SRW_FUTEX(word(), WAIT, l); }
inline void srw_lock_low::wake_one() { SRW_FUTEX(word(), WAKE, 1); }
inline void srw_lock_low::wake_all() { SRW_FUTEX(word(), WAKE, INT_MAX); }
inline void srw_lock_low::writer_wait(uint32_t l)
{
SRW_FUTEX(word(), WAIT, l);
}
inline void srw_lock_low::writer_wake() { SRW_FUTEX(word(), WAKE, 1); }
inline void srw_lock_low::readers_wake() { SRW_FUTEX(word(), WAKE, INT_MAX); }
# endif
# define readers_wait writer_wait
#endif
/** Wait for a read lock.
......@@ -99,7 +122,7 @@ void srw_lock_low::read_lock(uint32_t l)
#ifdef SRW_LOCK_DUMMY
pthread_mutex_lock(&mutex);
{
pthread_cond_signal(&cond);
pthread_cond_signal(&cond_ex);
pthread_cond_wait(&cond, &mutex);
l= value();
}
......@@ -107,7 +130,7 @@ void srw_lock_low::read_lock(uint32_t l)
pthread_mutex_unlock(&mutex);
continue;
#else
wake_one();
writer_wake();
#endif
}
else
......@@ -120,7 +143,7 @@ void srw_lock_low::read_lock(uint32_t l)
goto wake_writer;
}
wait(l);
readers_wait(l);
}
while (!read_trylock<true>(l));
}
......@@ -137,7 +160,7 @@ void srw_lock_low::update_lock(uint32_t l)
#ifdef SRW_LOCK_DUMMY
pthread_mutex_lock(&mutex);
{
pthread_cond_signal(&cond);
pthread_cond_signal(&cond_ex);
pthread_cond_wait(&cond, &mutex);
l= value();
}
......@@ -145,7 +168,7 @@ void srw_lock_low::update_lock(uint32_t l)
pthread_mutex_unlock(&mutex);
continue;
#else
wake_one();
writer_wake();
#endif
}
else
......@@ -158,7 +181,7 @@ void srw_lock_low::update_lock(uint32_t l)
goto wake_writer;
}
wait(l);
readers_wait(l);
}
while (!update_trylock(l));
}
......@@ -202,10 +225,10 @@ void srw_lock_low::write_lock(bool holding_u)
else
DBUG_ASSERT(~WRITER_WAITING & l);
wait(l);
writer_wait(l);
}
}
void srw_lock_low::rd_unlock() { if (read_unlock()) wake_one(); }
void srw_lock_low::u_unlock() { if (update_unlock()) wake_one(); }
void srw_lock_low::wr_unlock() { write_unlock(); wake_all(); }
void srw_lock_low::rd_unlock() { if (read_unlock()) writer_wake(); }
void srw_lock_low::u_unlock() { if (update_unlock()) writer_wake(); }
void srw_lock_low::wr_unlock() { write_unlock(); readers_wake(); }
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