major semaphore improvements (performance and correctness)

1. make sem_[timed]wait interruptible by signals, per POSIX
2. keep a waiter count in order to avoid unnecessary futex wake syscalls

diff --git a/src/thread/__timedwait.c b/src/thread/__timedwait.c
index 28b777b..a673099 100644 (file)
--- a/src/thread/__timedwait.c
+++ b/src/thread/__timedwait.c
@@ -18,6 +18,6 @@ int __timedwait(volatile int *addr, int val, clockid_t clk, const struct timespe
        }
        if (priv) priv = 128; priv=0;
        r = -__syscall(__NR_futex, (long)addr, FUTEX_WAIT | priv, val, at ? (long)&to : 0);
-       if (r == ETIMEDOUT) return r;
+       if (r == ETIMEDOUT || r == EINTR) return r;
        return 0;
 }

diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index 1439aac..7a19fc5 100644 (file)
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -16,7 +16,8 @@ int pthread_cond_timedwait(pthread_cond_t *c, pthread_mutex_t *m, const struct t
        if ((r=pthread_mutex_unlock(m))) return r;
 
        CANCELPT_BEGIN;
-       e = __timedwait(&c->_c_block, 1, c->_c_clock, ts, 0);
+       do e = __timedwait(&c->_c_block, 1, c->_c_clock, ts, 0);
+       while (e == EINTR);
        CANCELPT_END;
 
        pthread_cleanup_pop(0);

diff --git a/src/thread/sem_post.c b/src/thread/sem_post.c
index 0bd8a46..8f4700c 100644 (file)
--- a/src/thread/sem_post.c
+++ b/src/thread/sem_post.c
@@ -3,7 +3,8 @@
 
 int sem_post(sem_t *sem)
 {
-       if (!a_fetch_add(sem->__val, 1))
+       a_inc(sem->__val);
+       if (sem->__val[1])
                __wake(sem->__val, 1, 0);
        return 0;
 }

diff --git a/src/thread/sem_timedwait.c b/src/thread/sem_timedwait.c
index 11a0170..4f45c17 100644 (file)
--- a/src/thread/sem_timedwait.c
+++ b/src/thread/sem_timedwait.c
@@ -1,26 +1,41 @@
 #include <semaphore.h>
 #include "pthread_impl.h"
 
+static void cleanup(void *p)
+{
+       a_dec(p);
+}
+
 int sem_timedwait(sem_t *sem, const struct timespec *at)
 {
-       int val;
+       int r;
+
+       if (a_fetch_add(sem->__val, -1) > 0) return 0;
+       a_inc(sem->__val);
+
+       if (at && at->tv_nsec >= 1000000000UL) {
+               errno = EINVAL;
+               return -1;
+       }
+
+       a_inc(sem->__val+1);
+       pthread_cleanup_push(cleanup, sem->__val+1)
 
+       CANCELPT_BEGIN;
        for (;;) {
-               if (a_fetch_add(sem->__val, -1) > 0) return 0;
-               val = a_fetch_add(sem->__val, 1)+1;
-               if (val==1) __wake(sem->__val, 1, 0);
-               if (at && at->tv_nsec >= 1000000000UL) {
-                       errno = EINVAL;
-                       return -1;
-               }
-               CANCELPT_BEGIN;
-               if (val <= 0 && __timedwait(sem->__val, val, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
-                       errno = ETIMEDOUT;
-                       CANCELPT_TRY;
-                       CANCELPT_END;
-                       return -1;
+               r = 0;
+               if (!sem_trywait(sem)) break;
+               r = __timedwait(sem->__val, 0, CLOCK_REALTIME, at, 0);
+               if (r) {
+                       errno = r;
+                       r = -1;
+                       break;
                }
                CANCELPT_TRY;
-               CANCELPT_END;
        }
+       CANCELPT_END;
+
+       pthread_cleanup_pop(1);
+
+       return r;
 }

diff --git a/src/thread/sem_trywait.c b/src/thread/sem_trywait.c
index c5370c7..beb7aa5 100644 (file)
--- a/src/thread/sem_trywait.c
+++ b/src/thread/sem_trywait.c
@@ -3,9 +3,8 @@
 
 int sem_trywait(sem_t *sem)
 {
-       int val = a_fetch_add(sem->__val, -1);
-       if (val > 0) return 0;
-       if (!a_fetch_add(sem->__val, 1))
+       if (a_fetch_add(sem->__val, -1) > 0) return 0;
+       if (!a_fetch_add(sem->__val, 1) && sem->__val[1])
                __wake(sem->__val, 1, 0);
        errno = EAGAIN;
        return -1;