On 8/27/2011 1:37 PM, Corinna Vinschen wrote:
> On Aug 26 13:15, Corinna Vinschen wrote:
>> On Aug 25 17:39, David Rothenberger wrote:
>>> For a while now, the test cases that come with libapr1 have been
>>> bombing with this message:
>>>
>>> *** fatal error - NtCreateEvent(lock): 0xC0000035
>>>
>>> I finally took some time to investigate and have extracted a STC
>>> that demonstrates the problem.
>>
>> Thanks a lot for the testcase. In theory, the NtCreateEvent call should
>> not have happened at all, since it's called under lock, and the code
>> around that should have made sure that the object doesn't exist at the
>> time.
>>
>> After a few hours of extrem puzzlement, I now finally know what happens.
>> It's kinda hard to explain.
>>
[... very good description of flock problem ...]
>
> Please test the latest snapshot. It should fix this problem, as well as
> a starvation problem with signals (and, fwiw, thread cancel events) in
> flock, lockf, and POSIX fcntl locks.
The new snapshot runs the flock STC. Thanks!
I've been building libapr1 without F_SETLK support for a while since
it was also triggering the "NtCreateEvent(lock): 0xC0000035"
error. Since you mentioned fcntl, I tried re-enabling the fcntl
mutexes. They still trigger the error.
I've attached a similar STC that uses fcntl instead of flock.
--
David Rothenberger ---- daver...@acm.org
"It's what you learn after you know it all that counts."
-- John Wooden
/***********************************************************************
* This is a STC that causes the following error on my test machine:
* NtCreateEvent(lock): 0xC0000035
*
* It tries to use fcntl() for file locking. It creates a temporary
* file, the uses fork to spawn a number of children. Each child opens
* the file, then repeatedly uses fcntl to lock and unlock it.
*
* This test was extracted from the APR test suite.
*
* Compile: gcc -Wall -o stc-fcntl-fork stc-fcntl-fork.c
***********************************************************************/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/file.h>
#define MAX_ITER 2000
#define CHILDREN 6
/* A temporary file used for fcntl. */
char tmpfilename[] = "/tmp/fcntlXXXXXX";
struct flock mutex_lock_it;
struct flock mutex_unlock_it;
/* Fork and use fcntl to lock and unlock the file repeatedly in the child. */
void make_child(int trylock, pid_t *pid)
{
if ((*pid = fork()) < 0) {
perror("fork failed");
exit(1);
}
else if (*pid == 0) {
int fd2 = open(tmpfilename, O_RDWR);
if (fd2 < 0) {
perror("child open");
exit(1);
}
int rc;
int i;
for (i=0; i<MAX_ITER; ++i) {
do {
rc = fcntl(fd2, F_SETLKW, &mutex_lock_it);
} while (rc < 0 && errno == EINTR);
if (rc < 0) {
perror("lock");
exit(1);
}
do {
rc = fcntl(fd2, F_SETLKW, &mutex_unlock_it);
} while (rc < 0 && errno == EINTR);
if (rc < 0) {
perror("unlock");
exit(1);
}
}
exit(0);
}
}
/* Wait for the child to finish. */
void await_child(pid_t pid)
{
pid_t pstatus;
int exit_int;
do {
pstatus = waitpid(pid, &exit_int, WUNTRACED);
} while (pstatus < 0 && errno == EINTR);
}
int main(int argc, const char * const * argv, const char * const *env)
{
pid_t child[CHILDREN];
int n;
int fd;
/* Create the temporary file. */
fd = mkstemp(tmpfilename);
if (fd < 0) {
perror("open failed");
exit(1);
}
close(fd);
/* Setup mutexes */
mutex_lock_it.l_whence = SEEK_SET; /* from current point */
mutex_lock_it.l_start = 0; /* -"- */
mutex_lock_it.l_len = 0; /* until end of file */
mutex_lock_it.l_type = F_WRLCK; /* set exclusive/write lock */
mutex_lock_it.l_pid = 0; /* pid not actually interesting */
mutex_unlock_it.l_whence = SEEK_SET; /* from current point */
mutex_unlock_it.l_start = 0; /* -"- */
mutex_unlock_it.l_len = 0; /* until end of file */
mutex_unlock_it.l_type = F_UNLCK; /* set exclusive/write lock */
mutex_unlock_it.l_pid = 0; /* pid not actually interesting */
/* Create the children. */
for (n = 0; n < CHILDREN; n++)
make_child(0, &child[n]);
/* Wait for them to finish. */
for (n = 0; n < CHILDREN; n++)
await_child(child[n]);
/* Clean up. */
unlink(tmpfilename);
return 0;
}
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