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Date: Wed, 3 Jan 2018 14:17:12 +0100
From: Jens Gustedt <Jens.Gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: [PATCH 7/7] implement the local lock for condition variables with
 the new lock feature

Condition variables (pthread and C11) had a specialized lock
implementation that already had been designed such that no access to the
variable is made after an unlock. Here this is mandatory because the
implementation uses variables on the thread's stack to chain the access.

The previous implementation only held two different internal states, one
when there is no congestion and one when there is. The latter is then
used to wake up other threads if necessary.

The new lock structure deals with such situation more adequately, because
it keeps track of the exact congestion and allows us to react
appropriately.
---
 src/thread/pthread_cond_timedwait.c | 53 ++++++++++++-------------------------
 1 file changed, 17 insertions(+), 36 deletions(-)

diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index ed8569c2..659e9b5a 100644
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -1,5 +1,11 @@
 #include "pthread_impl.h"
 
+#if defined(__GNUC__) && defined(__PIC__)
+#define inline inline __attribute__((always_inline))
+#endif
+
+#include "__lock.h"
+
 void __pthread_testcancel(void);
 int __pthread_mutex_lock(pthread_mutex_t *);
 int __pthread_mutex_unlock(pthread_mutex_t *);
@@ -33,31 +39,6 @@ struct waiter {
 	volatile int *notify;
 };
 
-/* Self-synchronized-destruction-safe lock functions */
-
-static inline void lock(volatile int *l)
-{
-	if (a_cas(l, 0, 1)) {
-		a_cas(l, 1, 2);
-		do __wait(l, 0, 2, 1);
-		while (a_cas(l, 0, 2));
-	}
-}
-
-static inline void unlock(volatile int *l)
-{
-	if (a_swap(l, 0)==2)
-		__wake(l, 1, 1);
-}
-
-static inline void unlock_requeue(volatile int *l, volatile int *r, int w)
-{
-	a_store(l, 0);
-	if (w) __wake(l, 1, 1);
-	else __syscall(SYS_futex, l, FUTEX_REQUEUE|FUTEX_PRIVATE, 0, 1, r) != -ENOSYS
-		|| __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r);
-}
-
 enum {
 	WAITING,
 	SIGNALED,
@@ -84,7 +65,7 @@ int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restri
 		seq = c->_c_seq;
 		a_inc(&c->_c_waiters);
 	} else {
-		lock(&c->_c_lock);
+		__lock_fast(&c->_c_lock);
 
 		seq = node.barrier = 2;
 		fut = &node.barrier;
@@ -94,7 +75,7 @@ int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restri
 		if (!c->_c_tail) c->_c_tail = &node;
 		else node.next->prev = &node;
 
-		unlock(&c->_c_lock);
+		__unlock_fast(&c->_c_lock);
 	}
 
 	__pthread_mutex_unlock(m);
@@ -125,14 +106,14 @@ int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restri
 		 * after seeing a LEAVING waiter without getting notified
 		 * via the futex notify below. */
 
-		lock(&c->_c_lock);
-		
+		__lock_fast(&c->_c_lock);
+
 		if (c->_c_head == &node) c->_c_head = node.next;
 		else if (node.prev) node.prev->next = node.next;
 		if (c->_c_tail == &node) c->_c_tail = node.prev;
 		else if (node.next) node.next->prev = node.prev;
-		
-		unlock(&c->_c_lock);
+
+		__unlock_fast(&c->_c_lock);
 
 		if (node.notify) {
 			if (a_fetch_add(node.notify, -1)==1)
@@ -140,7 +121,7 @@ int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restri
 		}
 	} else {
 		/* Lock barrier first to control wake order. */
-		lock(&node.barrier);
+		__lock_fast(&node.barrier);
 	}
 
 relock:
@@ -156,7 +137,7 @@ relock:
 	/* Unlock the barrier that's holding back the next waiter, and
 	 * either wake it or requeue it to the mutex. */
 	if (node.prev)
-		unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
+		__unlock_requeue_fast(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
 	else
 		a_dec(&m->_m_waiters);
 
@@ -180,7 +161,7 @@ int __private_cond_signal(pthread_cond_t *c, int n)
 	volatile int ref = 0;
 	int cur;
 
-	lock(&c->_c_lock);
+	__lock_fast(&c->_c_lock);
 	for (p=c->_c_tail; n && p; p=p->prev) {
 		if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
 			ref++;
@@ -198,7 +179,7 @@ int __private_cond_signal(pthread_cond_t *c, int n)
 		c->_c_head = 0;
 	}
 	c->_c_tail = p;
-	unlock(&c->_c_lock);
+	__unlock_fast(&c->_c_lock);
 
 	/* Wait for any waiters in the LEAVING state to remove
 	 * themselves from the list before returning or allowing
@@ -206,7 +187,7 @@ int __private_cond_signal(pthread_cond_t *c, int n)
 	while ((cur = ref)) __wait(&ref, 0, cur, 1);
 
 	/* Allow first signaled waiter, if any, to proceed. */
-	if (first) unlock(&first->barrier);
+	if (first) __unlock_fast(&first->barrier);
 
 	return 0;
 }
-- 
2.15.1

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