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Proof of Concept: Allow to prevent fork from happening in known fork unsafe API

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[Feature #20590]

For better of for worse, fork(2) remain the primary provider of
parallelism in Ruby programs. Even though it's frowned uppon in
many circles, and a lot of literature will simply state that only
async-signal safe APIs are safe to use after `fork()`, in practice
most APIs work well as long as you are careful about not forking
while another thread is holding a pthread mutex.

One of the APIs that is known cause fork safety issues is `getaddrinfo`.
If you fork while another thread is inside `getaddrinfo`, a mutex
may be left locked in the child, with no way to unlock it.

I think we could reduce the impact of these problem by preventing
in for the most notorious and common cases, by locking around
`fork(2)` and known unsafe APIs with a read-write lock.
This commit is contained in:
Jean Boussier 2024-05-29 16:46:04 +02:00
parent 2e5680d304
commit 63cbe3f6ac
Notes: git 2024-09-05 09:44:04 +00:00
6 changed files with 82 additions and 2 deletions
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46
thread_pthread.c
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@ -3346,6 +3346,52 @@ native_sleep(rb_thread_t *th, rb_hrtime_t *rel)
RUBY_DEBUG_LOG("wakeup");
}
// fork read-write lock (only for pthread)
static pthread_rwlock_t rb_thread_fork_rw_lock = PTHREAD_RWLOCK_INITIALIZER;
void
rb_thread_release_fork_lock(void)
{
int r;
if ((r = pthread_rwlock_unlock(&rb_thread_fork_rw_lock))) {
rb_bug_errno("pthread_rwlock_unlock", r);
}
}
void
rb_thread_reset_fork_lock(void)
{
int r;
if ((r = pthread_rwlock_destroy(&rb_thread_fork_rw_lock))) {
rb_bug_errno("pthread_rwlock_destroy", r);
}
if ((r = pthread_rwlock_init(&rb_thread_fork_rw_lock, NULL))) {
rb_bug_errno("pthread_rwlock_init", r);
}
}
void *
rb_thread_prevent_fork(void *(*func)(void *), void *data)
{
int r;
if ((r = pthread_rwlock_rdlock(&rb_thread_fork_rw_lock))) {
rb_bug_errno("pthread_rwlock_rdlock", r);
}
void *result = func(data);
rb_thread_release_fork_lock();
return result;
}
void
rb_thread_acquire_fork_lock(void)
{
int r;
if ((r = pthread_rwlock_wrlock(&rb_thread_fork_rw_lock))) {
rb_bug_errno("pthread_rwlock_wrlock", r);
}
}
// thread internal event hooks (only for pthread)
struct rb_internal_thread_event_hook {