Add pthread_condattr_init/destroy/setpshared/getpshared
Note that this does not change the implementation of conditional variables
which still use shared futexes, independent on the flags being selected.
This will be fixed in a later patch, once our system is modified to use
pthread_condattr_setpshared(attr, PTHREAD_PROCESS_SHARED) properly.
Change-Id: I935de50964cd41f97a13dbfd6626d3407b0406c3
diff --git a/libc/bionic/pthread.c b/libc/bionic/pthread.c
index 127122f..4ffa9b8 100644
--- a/libc/bionic/pthread.c
+++ b/libc/bionic/pthread.c
@@ -1248,11 +1248,57 @@
return 0;
}
+int pthread_condattr_init(pthread_condattr_t *attr)
+{
+ if (attr == NULL)
+ return EINVAL;
+
+ *attr = PTHREAD_PROCESS_PRIVATE;
+ return 0;
+}
+
+int pthread_condattr_getpshared(pthread_condattr_t *attr, int *pshared)
+{
+ if (attr == NULL || pshared == NULL)
+ return EINVAL;
+
+ *pshared = *attr;
+ return 0;
+}
+
+int pthread_condattr_setpshared(pthread_condattr_t *attr, int pshared)
+{
+ if (attr == NULL)
+ return EINVAL;
+
+ if (pshared != PTHREAD_PROCESS_SHARED &&
+ pshared != PTHREAD_PROCESS_PRIVATE)
+ return EINVAL;
+
+ *attr = pshared;
+ return 0;
+}
+
+int pthread_condattr_destroy(pthread_condattr_t *attr)
+{
+ if (attr == NULL)
+ return EINVAL;
+
+ *attr = 0xdeada11d;
+ return 0;
+}
+
+/* We use one bit in condition variable values as the 'shared' flag
+ * The rest is a counter.
+ */
+#define COND_SHARING_MASK 0x0001
+#define COND_COUNTER_INCREMENT 0x0002
+#define COND_COUNTER_MASK (~COND_SHARING_MASK)
/* XXX *technically* there is a race condition that could allow
* XXX a signal to be missed. If thread A is preempted in _wait()
* XXX after unlocking the mutex and before waiting, and if other
- * XXX threads call signal or broadcast UINT_MAX times (exactly),
+ * XXX threads call signal or broadcast UINT_MAX/2 times (exactly),
* XXX before thread A is scheduled again and calls futex_wait(),
* XXX then the signal will be lost.
*/
@@ -1260,26 +1306,59 @@
int pthread_cond_init(pthread_cond_t *cond,
const pthread_condattr_t *attr)
{
+ if (cond == NULL)
+ return EINVAL;
+
cond->value = 0;
+
+ if (attr != NULL && *attr == PTHREAD_PROCESS_SHARED)
+ cond->value |= COND_SHARING_MASK;
+
return 0;
}
int pthread_cond_destroy(pthread_cond_t *cond)
{
+ if (cond == NULL)
+ return EINVAL;
+
cond->value = 0xdeadc04d;
return 0;
}
+/* This function is used by pthread_cond_broadcast and
+ * pthread_cond_signal to atomically decrement the counter.
+ */
+static void
+__pthread_cond_pulse(pthread_cond_t *cond)
+{
+ long flags = (cond->value & ~COND_COUNTER_MASK);
+
+ for (;;) {
+ long oldval = cond->value;
+ long newval = ((oldval - COND_COUNTER_INCREMENT) & COND_COUNTER_MASK)
+ | flags;
+ if (__atomic_cmpxchg(oldval, newval, &cond->value) == 0)
+ break;
+ }
+}
+
int pthread_cond_broadcast(pthread_cond_t *cond)
{
- __atomic_dec(&cond->value);
+ if (__unlikely(cond == NULL))
+ return EINVAL;
+
+ __pthread_cond_pulse(cond);
__futex_wake(&cond->value, INT_MAX);
return 0;
}
int pthread_cond_signal(pthread_cond_t *cond)
{
- __atomic_dec(&cond->value);
+ if (__unlikely(cond == NULL))
+ return EINVAL;
+
+ __pthread_cond_pulse(cond);
__futex_wake(&cond->value, 1);
return 0;
}