Support process shared condition variables

libc/intrin/pthread_mutex_lock.c

@@ -37,6 +37,7 @@ static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
   // get current state of lock
   word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
 
+#if PTHREAD_USE_NSYNC
   // use fancy nsync mutex if possible
   if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL &&        //
       MUTEX_PSHARED(word) == PTHREAD_PROCESS_PRIVATE &&  //
@@ -44,6 +45,7 @@ static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
     _weaken(nsync_mu_lock)((nsync_mu *)mutex);
     return 0;
   }
+#endif
 
   // implement barebones normal mutexes
   if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {

libc/intrin/pthread_mutex_trylock.c

@@ -46,6 +46,7 @@ errno_t pthread_mutex_trylock(pthread_mutex_t *mutex) {
   // get current state of lock
   word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
 
+#if PTHREAD_USE_NSYNC
   // delegate to *NSYNC if possible
   if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL &&
       MUTEX_PSHARED(word) == PTHREAD_PROCESS_PRIVATE &&  //
@@ -56,6 +57,7 @@ errno_t pthread_mutex_trylock(pthread_mutex_t *mutex) {
       return EBUSY;
     }
   }
+#endif
 
   // handle normal mutexes
   if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {

libc/intrin/pthread_mutex_unlock.c

@@ -45,6 +45,7 @@ errno_t pthread_mutex_unlock(pthread_mutex_t *mutex) {
   // get current state of lock
   word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
 
+#if PTHREAD_USE_NSYNC
   // use fancy nsync mutex if possible
   if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL &&        //
       MUTEX_PSHARED(word) == PTHREAD_PROCESS_PRIVATE &&  //
@@ -52,6 +53,7 @@ errno_t pthread_mutex_unlock(pthread_mutex_t *mutex) {
     _weaken(nsync_mu_unlock)((nsync_mu *)mutex);
     return 0;
   }
+#endif
 
   // implement barebones normal mutexes
   if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {

libc/intrin/pthread_yield_np.c

@@ -22,6 +22,8 @@
 #include "libc/runtime/syslib.internal.h"
 #include "libc/thread/thread.h"
 
+void sys_sched_yield(void);
+
 /**
  * Yields current thread's remaining timeslice to operating system.
  *
@@ -30,13 +32,16 @@
 int pthread_yield_np(void) {
   if (IsXnuSilicon()) {
     __syslib->__pthread_yield_np();
-  } else if (IsOpenbsd()) {
+  } else if (IsOpenbsd() || IsNetbsd()) {
-    pthread_pause_np();  // sched_yield() is punishingly slow on OpenBSD
+    // sched_yield() is punishingly slow on OpenBSD
+    // it's ruinously slow it'll destroy everything
+    pthread_pause_np();
   } else {
-    sched_yield();
+    sys_sched_yield();
   }
   return 0;
 }
 
 __weak_reference(pthread_yield_np, thrd_yield);
+__weak_reference(pthread_yield_np, sched_yield);
 __weak_reference(pthread_yield_np, pthread_yield);

libc/intrin/sys_sched_yield.S

@@ -19,12 +19,11 @@
 #include "libc/dce.h"
 #include "libc/sysv/consts/nr.h"
 #include "libc/macros.internal.h"
-.privileged
 
 //	Relinquishes scheduled quantum.
 //
 //	@return	0 on success, or -1 w/ errno
-sched_yield:
+sys_sched_yield:
 #ifdef __x86_64__
 	push	%rbp
 	mov	%rsp,%rbp
@@ -107,5 +106,5 @@ sched_yield:
 #else
 #error "arch unsupported"
 #endif
-	.endfn	sched_yield,globl
+	.endfn	sys_sched_yield,globl
 	.previous

libc/thread/pthread_cond_broadcast.c

@@ -1,7 +1,7 @@
 /*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
 │ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
 ╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│ Copyright 2024 Justine Alexandra Roberts Tunney                              │
 │                                                                              │
 │ Permission to use, copy, modify, and/or distribute this software for         │
 │ any purpose with or without fee is hereby granted, provided that the         │
@@ -16,8 +16,11 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/atomic.h"
+#include "libc/limits.h"
 #include "libc/thread/thread.h"
 #include "third_party/nsync/cv.h"
+#include "third_party/nsync/futex.internal.h"
 
 /**
  * Wakes all threads waiting on condition, e.g.
@@ -37,6 +40,19 @@
  * @see pthread_cond_wait
  */
 errno_t pthread_cond_broadcast(pthread_cond_t *cond) {
+
+#if PTHREAD_USE_NSYNC
+  // favor *NSYNC if this is a process private condition variable
+  // if using Mike Burrows' code isn't possible, use a naive impl
+  if (!cond->_pshared) {
     nsync_cv_broadcast((nsync_cv *)cond);
     return 0;
+  }
+#endif
+
+  // roll forward the monotonic sequence
+  atomic_fetch_add_explicit(&cond->_sequence, 1, memory_order_acq_rel);
+  if (atomic_load_explicit(&cond->_waiters, memory_order_acquire))
+    nsync_futex_wake_((atomic_int *)&cond->_sequence, INT_MAX, cond->_pshared);
+  return 0;
 }

libc/thread/pthread_cond_destroy.c

@@ -16,8 +16,11 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/errno.h"
+#include "libc/intrin/atomic.h"
 #include "libc/str/str.h"
 #include "libc/thread/thread.h"
+#include "third_party/nsync/cv.h"
 
 /**
  * Destroys condition.
@@ -26,6 +29,22 @@
  * @raise EINVAL if threads are still waiting on condition
  */
 errno_t pthread_cond_destroy(pthread_cond_t *cond) {
+
+  // check if there's active waiters
+#if PTHREAD_USE_NSYNC
+  if (cond->_pshared) {
+    if (((nsync_cv *)cond)->waiters)
+      return EINVAL;
+  } else {
+    if (atomic_load_explicit(&cond->_waiters, memory_order_relaxed))
+      return EINVAL;
+  }
+#else
+  if (atomic_load_explicit(&cond->_waiters, memory_order_relaxed))
+    return EINVAL;
+#endif
+
+  // destroy object
   memset(cond, -1, sizeof(*cond));
   return 0;
 }

libc/thread/pthread_cond_init.c

@@ -27,5 +27,7 @@
 errno_t pthread_cond_init(pthread_cond_t *cond,
                           const pthread_condattr_t *attr) {
   *cond = (pthread_cond_t){0};
+  if (attr)
+    cond->_pshared = *attr;
   return 0;
 }

libc/thread/pthread_cond_signal.c

@@ -16,8 +16,10 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/atomic.h"
 #include "libc/thread/thread.h"
 #include "third_party/nsync/cv.h"
+#include "third_party/nsync/futex.internal.h"
 
 /**
  * Wakes at least one thread waiting on condition, e.g.
@@ -37,6 +39,19 @@
  * @see pthread_cond_wait
  */
 errno_t pthread_cond_signal(pthread_cond_t *cond) {
+
+#if PTHREAD_USE_NSYNC
+  // favor *NSYNC if this is a process private condition variable
+  // if using Mike Burrows' code isn't possible, use a naive impl
+  if (!cond->_pshared) {
     nsync_cv_signal((nsync_cv *)cond);
     return 0;
+  }
+#endif
+
+  // roll forward the monotonic sequence
+  atomic_fetch_add_explicit(&cond->_sequence, 1, memory_order_acq_rel);
+  if (atomic_load_explicit(&cond->_waiters, memory_order_acquire))
+    nsync_futex_wake_((atomic_int *)&cond->_sequence, 1, cond->_pshared);
+  return 0;
 }

libc/thread/pthread_cond_timedwait.c

@@ -16,14 +16,61 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/calls/cp.internal.h"
 #include "libc/errno.h"
 #include "libc/thread/lock.h"
+#include "libc/thread/posixthread.internal.h"
 #include "libc/thread/thread.h"
 #include "libc/thread/thread2.h"
 #include "third_party/nsync/common.internal.h"
 #include "third_party/nsync/cv.h"
+#include "third_party/nsync/futex.internal.h"
 #include "third_party/nsync/time.h"
 
+struct PthreadWait {
+  pthread_cond_t *cond;
+  pthread_mutex_t *mutex;
+};
+
+static void pthread_cond_leave(void *arg) {
+  struct PthreadWait *wait = (struct PthreadWait *)arg;
+  if (pthread_mutex_lock(wait->mutex))
+    __builtin_trap();
+  atomic_fetch_sub_explicit(&wait->cond->_waiters, 1, memory_order_acq_rel);
+}
+
+static errno_t pthread_cond_timedwait_impl(pthread_cond_t *cond,
+                                           pthread_mutex_t *mutex,
+                                           const struct timespec *abstime) {
+
+  // this is a cancelation point
+  // check the cancelation status before we begin waiting
+  if (pthread_testcancel_np() == ECANCELED)
+    return ECANCELED;
+
+  // get original monotonic sequence while lock is held
+  uint32_t seq1 = atomic_load_explicit(&cond->_sequence, memory_order_relaxed);
+
+  // start waiting on condition variable
+  atomic_fetch_add_explicit(&cond->_waiters, 1, memory_order_acq_rel);
+  if (pthread_mutex_unlock(mutex))
+    __builtin_trap();
+
+  // wait for sequence change, timeout, or cancelation
+  int rc;
+  struct PthreadWait waiter = {cond, mutex};
+  pthread_cleanup_push(pthread_cond_leave, &waiter);
+  rc = nsync_futex_wait_((atomic_int *)&cond->_sequence, seq1, cond->_pshared,
+                         abstime);
+  pthread_cleanup_pop(true);
+  if (rc == -EAGAIN)
+    rc = 0;
+
+  // turn linux syscall status into posix errno
+  return -rc;
+}
+
 /**
  * Waits for condition with optional time limit, e.g.
  *
@@ -49,11 +96,39 @@
  */
 errno_t pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
                                const struct timespec *abstime) {
+
+  // validate arguments
+  struct PosixThread *pt;
+  if (!(pt = _pthread_self()))
+    return EINVAL;
   if (abstime && !(0 <= abstime->tv_nsec && abstime->tv_nsec < 1000000000))
     return EINVAL;
-  if (MUTEX_TYPE(mutex->_word) != PTHREAD_MUTEX_NORMAL)
+
-    nsync_panic_("pthread cond needs normal mutex\n");
+  // look at the mutex argument
+  uint64_t muword = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
+
+  // check that mutex is held by caller
+  if (MUTEX_TYPE(muword) == PTHREAD_MUTEX_ERRORCHECK &&
+      MUTEX_OWNER(muword) != gettid())
+    return EPERM;
+
+  // if condition variable is shared then mutex must be too
+  if (cond->_pshared)
+    if (MUTEX_PSHARED(muword) != PTHREAD_PROCESS_SHARED)
+      return EINVAL;
+
+#if PTHREAD_USE_NSYNC
+  // favor *NSYNC if this is a process private condition variable
+  // if using Mike Burrows' code isn't possible, use a naive impl
+  if (!cond->_pshared)
     return nsync_cv_wait_with_deadline(
         (nsync_cv *)cond, (nsync_mu *)mutex,
         abstime ? *abstime : nsync_time_no_deadline, 0);
+#endif
+
+  errno_t err;
+  BEGIN_CANCELATION_POINT;
+  err = pthread_cond_timedwait_impl(cond, mutex, abstime);
+  END_CANCELATION_POINT;
+  return err;
 }

libc/thread/sem_open.c

@@ -183,7 +183,8 @@ sem_t *sem_open(const char *name, int oflag, ...) {
 #if 0
   if (IsXnuSilicon()) {
     long kernel;
-    if (!(sem = calloc(1, sizeof(sem_t)))) return SEM_FAILED;
+    if (!(sem = calloc(1, sizeof(sem_t))))
+      return SEM_FAILED;
     sem->sem_magic = SEM_MAGIC_KERNEL;
     kernel = _sysret(__syslib->__sem_open(name, oflag, mode, value));
     if (kernel == -1) {

libc/thread/sem_timedwait.c

@@ -81,13 +81,15 @@ int sem_timedwait(sem_t *sem, const struct timespec *abstime) {
         return ecanceled();
       }
       rc = _sysret(__syslib->__sem_trywait(sem->sem_kernel));
-      if (!rc) return 0;
+      if (!rc)
+        return 0;
       if (errno == EINTR &&                  //
           _weaken(pthread_testcancel_np) &&  //
           _weaken(pthread_testcancel_np)()) {
         return ecanceled();
       }
-      if (errno != EAGAIN) return -1;
+      if (errno != EAGAIN)
+        return -1;
       errno = e;
       struct timespec now = timespec_real();
       if (timespec_cmp(*abstime, now) >= 0) {

libc/thread/thread.h

@@ -3,6 +3,7 @@
 
 #define PTHREAD_KEYS_MAX              46
 #define PTHREAD_STACK_MIN             65536
+#define PTHREAD_USE_NSYNC             1
 #define PTHREAD_DESTRUCTOR_ITERATIONS 4
 
 #define PTHREAD_BARRIER_SERIAL_THREAD 31337
@@ -74,7 +75,15 @@ typedef struct pthread_mutexattr_s {
 } pthread_mutexattr_t;
 
 typedef struct pthread_cond_s {
-  void *_nsync[2];
+  union {
+    void *_align;
+    struct {
+      uint32_t _nsync;
+      char _pshared;
+    };
+  };
+  _Atomic(uint32_t) _sequence;
+  _Atomic(uint32_t) _waiters;
 } pthread_cond_t;
 
 typedef struct pthread_rwlock_s {

test/posix/mutex_async_signal_safety_test.c

@@ -66,7 +66,7 @@ int main() {
     if (ready)
       break;
 
-  for (int i = 0; i < 1000; ++i) {
+  for (int i = 0; i < 100; ++i) {
     if (pthread_kill(th, SIGUSR1))
       _Exit(11);
     if (pthread_kill(th, SIGUSR1))