From 8d81ba8c0bc6fe31136cb15c9c82ef4c24965040 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Fri, 22 May 2020 17:45:47 -0400 Subject: restore lock-skipping for processes that return to single-threaded state the design used here relies on the barrier provided by the first lock operation after the process returns to single-threaded state to synchronize with actions by the last thread that exited. by storing the intent to change modes in the same object used to detect whether locking is needed, it's possible to avoid an extra (possibly costly) memory load after the lock is taken. --- src/thread/pthread_create.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'src/thread/pthread_create.c') diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c index 6a3b0c21..6bdfb44f 100644 --- a/src/thread/pthread_create.c +++ b/src/thread/pthread_create.c @@ -118,8 +118,8 @@ _Noreturn void __pthread_exit(void *result) * until the lock is released, which only happens after SYS_exit * has been called, via the exit futex address pointing at the lock. * This needs to happen after any possible calls to LOCK() that might - * skip locking if libc.threads_minus_1 is zero. */ - libc.threads_minus_1--; + * skip locking if process appears single-threaded. */ + if (!--libc.threads_minus_1) libc.need_locks = -1; self->next->prev = self->prev; self->prev->next = self->next; self->prev = self->next = self; @@ -339,7 +339,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long)))); __tl_lock(); - libc.threads_minus_1++; + if (!libc.threads_minus_1++) libc.need_locks = 1; ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock); /* All clone failures translate to EAGAIN. If explicit scheduling @@ -363,7 +363,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att new->next->prev = new; new->prev->next = new; } else { - libc.threads_minus_1--; + if (!--libc.threads_minus_1) libc.need_locks = 0; } __tl_unlock(); __restore_sigs(&set); -- cgit v1.2.1