sqlrelay-discussion

[Sqlrelay-discussion] statistics and shm access without semaphores

[Renat S. <sr...@st...>]

I'm afraid I've found the cause of strange statistics

look at this code in sqllistener.C :

	shmdata	*ptr=(shmdata *)staticlistener->idmemory->getPointer();
	ptr->statistics.forked_listeners--;

If 2 processes simultaniously get access to shared memory and, for 
example, in this moment forked_listeners = 10, then they both decrease 
this value to 9 and put back to shared memory. As result would be 9 
instead of 8.

Solution ids obvious: semaphores should be used to access shared memory.

For example:

	shmdata	*ptr=(shmdata *)staticlistener->idmemory->getPointer();
	sem_t *mutex=staticlistener->idmemory->getSemaphore();
	sem_wait(mutex);
	ptr->statistics.forked_listeners--;
	sem_post(mutex);


-- 
Renat Sabitov   e-mail: sr...@st...
Stack Soft         jid: sr...@ja...

Re: [Sqlrelay-discussion] statistics and shm access without semaphores

[Renat S. <sr...@st...>]

Renat Sabitov пишет:

> Solution ids obvious: semaphores should be used to access shared memory.

I have made a patch for sqlrelay-0.41 which use mutex #9 to access 
statistics shared memory.

-- 
Renat Sabitov   e-mail: sr...@st...
Stack Soft         jid: sr...@ja...