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Not re-enable background thread after fork.

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Avoid calling pthread_create in postfork handlers.
This commit is contained in:
Qi Wang 2017-06-09 00:00:48 -07:00 committed by Qi Wang
parent 464cb60490
commit b83b5ad44a
3 changed files with 49 additions and 36 deletions
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5
doc/jemalloc.xml.in
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@ -750,7 +750,10 @@ mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".decay",
background threads will be no more than the number of CPUs or active
arenas). Threads run periodically, and handle <link
linkend="arena.i.decay">purging</link> asynchronously. When switching
off, background threads are terminated synchronously. See <link
off, background threads are terminated synchronously. Note that after
<citerefentry><refentrytitle>fork</refentrytitle><manvolnum>2</manvolnum></citerefentry>
function, the state in the child process will be disabled regardless
the state in parent process. See <link
linkend="stats.background_thread.num_threads"><mallctl>stats.background_thread</mallctl></link>
for related stats. <link
linkend="opt.background_thread"><mallctl>opt.background_thread</mallctl></link>

79
src/background_thread.c
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@ -350,24 +350,38 @@ check_background_thread_creation(tsd_t *tsd, unsigned *n_created,
}
background_thread_info_t *info = &background_thread_info[i];
malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
if (info->started) {
pre_reentrancy(tsd);
int err = pthread_create_wrapper(&info->thread, NULL,
background_thread_entry, (void *)(uintptr_t)i);
post_reentrancy(tsd);
if (err == 0) {
(*n_created)++;
created_threads[i] = true;
} else {
malloc_printf("<jemalloc>: background thread "
"creation failed (%d)\n", err);
if (opt_abort) {
abort();
}
bool create = info->started;
malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
if (!create) {
continue;
}
/*
* To avoid deadlock with prefork handlers (which waits for the
* mutex held here), unlock before calling pthread_create().
*/
malloc_mutex_unlock(tsd_tsdn(tsd),
&background_thread_info[0].mtx);
pre_reentrancy(tsd);
int err = pthread_create_wrapper(&info->thread, NULL,
background_thread_entry, (void *)(uintptr_t)i);
post_reentrancy(tsd);
malloc_mutex_lock(tsd_tsdn(tsd),
&background_thread_info[0].mtx);
if (err == 0) {
(*n_created)++;
created_threads[i] = true;
} else {
malloc_printf("<jemalloc>: background thread "
"creation failed (%d)\n", err);
if (opt_abort) {
abort();
}
}
malloc_mutex_unlock(tsd_tsdn(tsd), &info->mtx);
/* Since we unlocked and may miss signals, restart. */
i = 1;
}
}
@ -643,14 +657,7 @@ label_done:
void
background_thread_prefork0(tsdn_t *tsdn) {
malloc_mutex_prefork(tsdn, &background_thread_lock);
if (background_thread_enabled()) {
background_thread_enabled_at_fork = true;
background_thread_enabled_set(tsdn, false);
background_threads_disable(tsdn_tsd(tsdn));
} else {
background_thread_enabled_at_fork = false;
}
assert(n_background_threads == 0);
background_thread_enabled_at_fork = background_thread_enabled();
}
void
@ -660,22 +667,12 @@ background_thread_prefork1(tsdn_t *tsdn) {
}
}
static void
background_thread_postfork_init(tsdn_t *tsdn) {
assert(n_background_threads == 0);
if (background_thread_enabled_at_fork) {
background_thread_enabled_set(tsdn, true);
background_threads_enable(tsdn_tsd(tsdn));
}
}
void
background_thread_postfork_parent(tsdn_t *tsdn) {
for (unsigned i = 0; i < ncpus; i++) {
malloc_mutex_postfork_parent(tsdn,
&background_thread_info[i].mtx);
}
background_thread_postfork_init(tsdn);
malloc_mutex_postfork_parent(tsdn, &background_thread_lock);
}
@ -686,9 +683,23 @@ background_thread_postfork_child(tsdn_t *tsdn) {
&background_thread_info[i].mtx);
}
malloc_mutex_postfork_child(tsdn, &background_thread_lock);
if (!background_thread_enabled_at_fork) {
return;
}
/* Clear background_thread state (reset to disabled for child). */
malloc_mutex_lock(tsdn, &background_thread_lock);
background_thread_postfork_init(tsdn);
n_background_threads = 0;
background_thread_enabled_set(tsdn, false);
for (unsigned i = 0; i < ncpus; i++) {
background_thread_info_t *info = &background_thread_info[i];
malloc_mutex_lock(tsdn, &info->mtx);
info->started = false;
int ret = pthread_cond_init(&info->cond, NULL);
assert(ret == 0);
background_thread_info_init(tsdn, info);
malloc_mutex_unlock(tsdn, &info->mtx);
}
malloc_mutex_unlock(tsdn, &background_thread_lock);
}

1
src/jemalloc.c
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@ -340,7 +340,6 @@ arena_new_create_background_thread(tsdn_t *tsdn, unsigned ind) {
if (ind == 0) {
return;
}
/* background_thread_create() handles reentrancy internally. */
if (have_background_thread) {
bool err;
malloc_mutex_lock(tsdn, &background_thread_lock);