implement robust mutexes

some of this code should be cleaned up, e.g. using macros for some of
the bit flags, masks, etc. nonetheless, the code is believed to be
working and correct at this point.

include/pthread.h

@@ -92,6 +92,7 @@ int pthread_mutex_unlock(pthread_mutex_t *);
 int pthread_mutex_trylock(pthread_mutex_t *);
 int pthread_mutex_timedlock(pthread_mutex_t *, const struct timespec *);
 int pthread_mutex_destroy(pthread_mutex_t *);
+int pthread_mutex_consistent(pthread_mutex_t *);
 
 int pthread_cond_init(pthread_cond_t *, const pthread_condattr_t *);
 int pthread_cond_destroy(pthread_cond_t *);

src/internal/pthread_impl.h

@@ -37,6 +37,11 @@ struct pthread {
 	void **tsd;
 	pthread_attr_t attr;
 	volatile int dead;
+	struct {
+		void **head;
+		long off;
+		void *pending;
+	} robust_list;
 };
 
 #define __SU (sizeof(size_t)/sizeof(int))

src/thread/pthread_mutex_consistent.c

+#include "pthread_impl.h"
+
+int pthread_mutex_consistent(pthread_mutex_t *m)
+{
+	if (m->_m_type < 8) return EINVAL;
+	if ((m->_m_lock & 0x3fffffff) != pthread_self()->tid)
+		return EPERM;
+	m->_m_type -= 8;
+	return 0;
+}

src/thread/pthread_mutex_init.c

@@ -3,6 +3,6 @@
 int pthread_mutex_init(pthread_mutex_t *m, const pthread_mutexattr_t *a)
 {
 	memset(m, 0, sizeof *m);
-	if (a) m->_m_type = *a & 3;
+	if (a) m->_m_type = *a & 7;
 	return 0;
 }

src/thread/pthread_mutex_lock.c

@@ -4,9 +4,9 @@ int pthread_mutex_lock(pthread_mutex_t *m)
 {
 	int r;
 	while ((r=pthread_mutex_trylock(m)) == EBUSY) {
-		if (!(r=m->_m_lock)) continue;
-		if (m->_m_type == PTHREAD_MUTEX_ERRORCHECK
-		 && r == pthread_self()->tid)
+		if (!(r=m->_m_lock) || (r&0x40000000)) continue;
+		if ((m->_m_type&3) == PTHREAD_MUTEX_ERRORCHECK
+		 && (r&0x1fffffff) == pthread_self()->tid)
 			return EDEADLK;
 		__wait(&m->_m_lock, &m->_m_waiters, r, 0);
 	}

src/thread/pthread_mutex_timedlock.c

@@ -4,8 +4,9 @@ int pthread_mutex_timedlock(pthread_mutex_t *m, const struct timespec *at)
 {
 	int r, w=0;
 	while ((r=pthread_mutex_trylock(m)) == EBUSY) {
+		if (!(r=m->_m_lock) || (r&0x40000000)) continue;
 		if (!w) a_inc(&m->_m_waiters), w++;
-		if (__timedwait(&m->_m_lock, 1, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
+		if (__timedwait(&m->_m_lock, r, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
 			if (w) a_dec(&m->_m_waiters);
 			return ETIMEDOUT;
 		}

src/thread/pthread_mutex_trylock.c

@@ -3,19 +3,51 @@
 int pthread_mutex_trylock(pthread_mutex_t *m)
 {
 	int tid;
+	int own;
+	pthread_t self;
 
 	if (m->_m_type == PTHREAD_MUTEX_NORMAL)
 		return (m->_m_lock || a_swap(&m->_m_lock, 1)) ? EBUSY : 0;
 
-	tid = pthread_self()->tid;
+	self = pthread_self();
+	tid = self->tid | 0x80000000;
 
-	if (m->_m_lock == tid && m->_m_type == PTHREAD_MUTEX_RECURSIVE) {
+	if (m->_m_type >= 4) {
+		if (!self->robust_list.off)
+			syscall2(__NR_set_robust_list,
+				(long)&self->robust_list, 3*sizeof(long));
+		self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
+		self->robust_list.pending = &m->_m_next;
+	}
+
+	if (m->_m_lock == tid && (m->_m_type&3) == PTHREAD_MUTEX_RECURSIVE) {
 		if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
 		m->_m_count++;
 		return 0;
 	}
 
-	if (m->_m_lock || a_cas(&m->_m_lock, 0, tid)) return EBUSY;
+	own = m->_m_lock;
+	if ((own && !(own & 0x40000000)) || a_cas(&m->_m_lock, own, tid)!=own)
+		return EBUSY;
+
 	m->_m_count = 1;
+
+	if (m->_m_type < 4) return 0;
+
+	if (m->_m_type >= 8) {
+		m->_m_lock = 0;
+		return ENOTRECOVERABLE;
+	}
+	m->_m_next = self->robust_list.head;
+	m->_m_prev = &self->robust_list.head;
+	if (self->robust_list.head)
+		self->robust_list.head[-1] = &m->_m_next;
+	self->robust_list.head = &m->_m_next;
+	self->robust_list.pending = 0;
+	if (own) {
+		m->_m_type += 8;
+		return EOWNERDEAD;
+	}
+
 	return 0;
 }

src/thread/pthread_mutex_unlock.c

@@ -2,14 +2,23 @@
 
 int pthread_mutex_unlock(pthread_mutex_t *m)
 {
+	pthread_t self;
+
 	if (m->_m_type != PTHREAD_MUTEX_NORMAL) {
-		if (!m->_m_lock || m->_m_lock != __pthread_self()->tid)
+		self = __pthread_self();
+		if ((m->_m_lock&0x1fffffff) != self->tid)
 		 	return EPERM;
-		if (m->_m_type == PTHREAD_MUTEX_RECURSIVE && --m->_m_count)
+		if ((m->_m_type&3) == PTHREAD_MUTEX_RECURSIVE && --m->_m_count)
 			return 0;
+		if (m->_m_type >= 4) {
+			self->robust_list.pending = &m->_m_next;
+			*(void **)m->_m_prev = m->_m_next;
+			if (m->_m_next) ((void **)m->_m_next)[-1] = m->_m_prev;
+		}
 	}
 
 	m->_m_lock = 0;
 	if (m->_m_waiters) __wake(&m->_m_lock, 1, 0);
+	if (m->_m_type >= 4) self->robust_list.pending = 0;
 	return 0;
 }

src/thread/pthread_mutexattr_getrobust.c

+#include "pthread_impl.h"
+
+int pthread_mutexattr_getrobust(const pthread_mutexattr_t *a, int *robust)
+{
+	*robust = *a / 4U % 2;
+	return 0;
+}

src/thread/pthread_mutexattr_setrobust.c

+#include "pthread_impl.h"
+
+int pthread_mutexattr_setrobust(pthread_mutexattr_t *a, int robust)
+{
+	if (robust > 1U) return EINVAL;
+	*a &= ~4;
+	*a |= robust*4;
+	return 0;
+}