"Gregory Stark" <[EMAIL PROTECTED]> writes:
> "Gregory Stark" <[EMAIL PROTECTED]> writes:
>
>> "Tom Lane" <[EMAIL PROTECTED]> writes:
>>
>>> Gregory Stark <[EMAIL PROTECTED]> writes:
>>>> We're seeing a problem where occasionally a process appears to be granted a
>>>> lock but miss its semaphore signal.
>>>
>>> Kernel bug maybe? What's the platform?
I've written a synthetic test program to check for lost semaphore wakeups. I
can't seem to produce any on my machine but haven't had a chance to run it yet
on the benchmark machine that's been showing the problem.
If I can't produce any lost wakeups with a program like this it looks more
like it might be a Postgres or GCC bug than a Linux bug.
It would be helpful if people could run this on various architectures and
various versions of Linux (or other OSes). I've been running it with 40
processes for an hour, but even shorter runs would be useful. It will drive
the load on your machine through the roof but doesn't cause any i/o.
$ gcc -Wall ipctest.c -lrt
$ ./a.out 40 3600
#include <stdlib.h>
#include <stdio.h>
#include <semaphore.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <signal.h>
#define IPCProtection (0600) /* access/modify by user only */
int nthreads;
sem_t *sems;
unsigned char *wakers;
static void worker(int n);
int main(int argc, char *argv[])
{
int i, shmid1, shmid2, runtime;
pid_t *pids;
if (argc <= 1)
nthreads = 10;
else
nthreads = atoi(argv[1]);
if (argc <= 2)
runtime = 10;
else
runtime = atoi(argv[2]);
if (nthreads <= 0 || nthreads > 200)
exit(1);
if (runtime <= 0)
exit(1);
printf("running with %d processes for %ds\n", nthreads, runtime);
shmid1 = shmget(IPC_PRIVATE, nthreads*sizeof(sem_t), IPC_CREAT | IPC_EXCL | IPCProtection);
if (shmid1 == -1) {
perror("shmget:");
exit(1);
}
sems = shmat(shmid1, NULL, 0);
for (i=0;i<nthreads;i++)
if (sem_init(&sems[i], 1, 0) < 0) {
perror("sem_init");
exit(1);
}
shmid2 = shmget(IPC_PRIVATE, nthreads*sizeof(unsigned char), IPC_CREAT | IPC_EXCL | IPCProtection);
if (shmid2 == -1) {
perror("shmget:");
exit(1);
}
wakers = shmat(shmid2, NULL, 0);
for (i=0;i<nthreads;i++)
wakers[i] = 255;
pids = malloc(sizeof(pid_t)*nthreads);
for (i=0;i<nthreads;i++) {
/*printf("forking thread %d\n", i);*/
switch(pids[i] = fork()) {
case 0:
worker(i);
exit(0);
case -1:
perror("fork");
exit(1);
default:
/*printf("successfully forked thread %d as pid %d\n", i, pids[i]);*/
break;
}
}
sleep(runtime);
kill(pids[0], 3);
sleep(1);
for (i=1;i<nthreads;i++) {
if (wakers[i] == 255)
printf("thread %d lost a wakeup!!!\n", i);
kill(pids[i], 3);
}
if (shmctl(shmid1, IPC_RMID, NULL) < 0)
perror("smctl ipc_rmid");
if (shmctl(shmid2, IPC_RMID, NULL) < 0)
perror("smctl ipc_rmid");
exit(0);
}
static void worker(int n)
{
srandom(getpid());
for(;;) {
int waker;
int i;
/* wake anyone following us waiting for us to wake them */
for (i=n+1;i<nthreads;i++) {
if (wakers[i] == n) {
/*printf("thread %d waking thread %d\n", n, i);*/
wakers[i] = 255;
if (sem_post(&sems[i]) < 0) {
perror("sem_post");
exit(1);
}
}
}
if (n == 0) {
/* we're the first thread so we just sleep and then go around waking
people again */
continue;
}
/* otherwise pick a random thread earlier than us to wake us and go to
sleep until awoken by it */
waker = random()%n;
/*printf("thread %d sleeping waiting for %d to wake us\n", n, waker);*/
wakers[n] = waker;
if (sem_wait(&sems[n]) < 0) {
perror("sem_wait");
exit(1);
}
if ((waker = wakers[n]) != 255) {
printf("thread %d awake but waker is still set to %d !!!!\n", n, waker);
exit(1);
}
/*printf("thread %d awoken\n", n);*/
}
}
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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