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rearrange jl_delete_thread to be thread-safe #56097

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Oct 11, 2024
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rearrange jl_delete_thread to be thread-safe #56097

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46 changes: 25 additions & 21 deletions src/threading.c
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Original file line number Diff line number Diff line change
Expand Up @@ -464,6 +464,30 @@ static void jl_delete_thread(void *value) JL_NOTSAFEPOINT_ENTER
// prior unsafe-region (before we let it release the stack memory)
(void)jl_gc_unsafe_enter(ptls);
scheduler_delete_thread(ptls);
// need to clear pgcstack and eh, but we can clear everything now too
jl_task_t *ct = jl_atomic_load_relaxed(&ptls->current_task);
jl_task_frame_noreturn(ct);
if (jl_set_task_tid(ptls->root_task, ptls->tid)) {
// the system will probably free this stack memory soon
// so prevent any other thread from accessing it later
if (ct != ptls->root_task)
jl_task_frame_noreturn(ptls->root_task);
}
else {
// Uh oh. The user cleared the sticky bit so it started running
// elsewhere, then called pthread_exit on this thread from another
// Task, which will free the stack memory of that root task soon. This
// is not recoverable. Though we could just hang here, a fatal message
// is likely better.
jl_safe_printf("fatal: thread exited from wrong Task.\n");
abort();
}
ptls->previous_exception = NULL;
// allow the page root_task is on to be freed
ptls->root_task = NULL;
jl_free_thread_gc_state(ptls);
// park in safe-region from here on (this may run GC again)
(void)jl_gc_safe_enter(ptls);
// try to free some state we do not need anymore
#ifndef _OS_WINDOWS_
void *signal_stack = ptls->signal_stack;
Expand Down Expand Up @@ -502,21 +526,7 @@ static void jl_delete_thread(void *value) JL_NOTSAFEPOINT_ENTER
#else
pthread_mutex_lock(&in_signal_lock);
#endif
// need to clear pgcstack and eh, but we can clear everything now too
jl_task_frame_noreturn(jl_atomic_load_relaxed(&ptls->current_task));
if (jl_set_task_tid(ptls->root_task, ptls->tid)) {
// the system will probably free this stack memory soon
// so prevent any other thread from accessing it later
jl_task_frame_noreturn(ptls->root_task);
}
else {
// Uh oh. The user cleared the sticky bit so it started running
// elsewhere, then called pthread_exit on this thread. This is not
// recoverable. Though we could just hang here, a fatal message is better.
jl_safe_printf("fatal: thread exited from wrong Task.\n");
abort();
}
jl_atomic_store_relaxed(&ptls->current_task, NULL); // dead
jl_atomic_store_relaxed(&ptls->current_task, NULL); // indicate dead
// finally, release all of the locks we had grabbed
#ifdef _OS_WINDOWS_
jl_unlock_profile_wr();
Expand All @@ -529,12 +539,6 @@ static void jl_delete_thread(void *value) JL_NOTSAFEPOINT_ENTER
#endif
free(ptls->bt_data);
small_arraylist_free(&ptls->locks);
ptls->previous_exception = NULL;
// allow the page root_task is on to be freed
ptls->root_task = NULL;
jl_free_thread_gc_state(ptls);
// then park in safe-region
(void)jl_gc_safe_enter(ptls);
}

//// debugging hack: if we are exiting too fast for error message printing on threads,
Expand Down
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