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Improved handling of shm/semaphores w.r.t. stale states (#199)

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Wolfgang Hommel
2019-08-20 09:53:22 +02:00
parent 65cdc7b718
commit c13e41024e
1 changed files with 33 additions and 2 deletions
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35
src/libfaketime.c
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@@ -375,8 +375,17 @@ static void ft_shm_destroy(void)
printf("libfaktime: In ft_shm_destroy(), error parsing semaphore name and shared memory id from string: %s", ft_shared_env);
exit(1);
}
/*
To avoid shared memory / semaphores left after quitting, we have to clean
up here similar to how the faketime wrapper does.
However, there is no guarantee that all child processes have quit before
we clean up here, which potentially leaves us in a stale state.
Since there is no easy solution for this problem (see issue #56),
ft_shm_init() below at least tries to handle this carefully.
*/
sem_unlink(sem_name);
sem_unlink(shm_name);
unsetenv("FAKETIME_SHARED");
}
}
@@ -384,13 +393,35 @@ static void ft_shm_init (void)
{
int ticks_shm_fd;
char sem_name[256], shm_name[256], *ft_shared_env = getenv("FAKETIME_SHARED");
sem_t *shared_semR = NULL;
/* create semaphore and shared memory locally unless it has been passed along */
if (ft_shared_env == NULL)
{
ft_shm_create();
ft_shared_env = getenv("FAKETIME_SHARED");
}
/* check for stale semaphore / shared memory information */
if (ft_shared_env != NULL)
{
if (sscanf(ft_shared_env, "%255s %255s", sem_name, shm_name) < 2)
{
printf("libfaketime: In ft_shm_init(), error parsing semaphore name and shared memory id from string: %s", ft_shared_env);
exit(1);
}
if (SEM_FAILED == (shared_semR = sem_open(sem_name, 0))) /* gone stale? */
{
ft_shm_create();
ft_shared_env = getenv("FAKETIME_SHARED");
}
else
{
sem_close(shared_semR);
}
}
/* process the semaphore / shared memory information */
if (ft_shared_env != NULL)
{
if (sscanf(ft_shared_env, "%255s %255s", sem_name, shm_name) < 2)
@@ -402,8 +433,8 @@ static void ft_shm_init (void)
if (SEM_FAILED == (shared_sem = sem_open(sem_name, 0)))
{
perror("libfaketime: In ft_shm_init(), sem_open failed");
fprintf(stderr, "libfaketime: sem_name was %s, created locally: %s", sem_name, shmCreator ? "true":"false");
fprintf(stderr, "libfaketime: parsed from env: %s", ft_shared_env);
fprintf(stderr, "libfaketime: sem_name was %s, created locally: %s\n", sem_name, shmCreator ? "true":"false");
fprintf(stderr, "libfaketime: parsed from env: %s\n", ft_shared_env);
exit(1);
}