libroot: Implemented pthread barriers

This is an implementation of pthread barriers pursuant to the relevant specification.

Barriers are essentially a special case of conditional variables,
such that all threads waiting on one are woken up when the number of
waiters reaches a number provided at the initialization of the barrier.
In view of that, this implementation mimics the implementation of pthread_cond,
except it is more specialized and self-contained.

Signed-off-by: Jérôme Duval <[email protected]>

headers/posix/pthread.h

@@ -114,6 +114,20 @@ extern int pthread_mutexattr_setpshared(pthread_mutexattr_t *mutexAttr,
 	int processShared);
 extern int pthread_mutexattr_settype(pthread_mutexattr_t *mutexAttr, int type);
 
+/* barrier functions */
+extern int pthread_barrier_init(pthread_barrier_t *barrier,
+	const pthread_barrierattr_t *attr, unsigned count);
+extern int pthread_barrier_destroy(pthread_barrier_t *barrier);
+extern int pthread_barrier_wait(pthread_barrier_t *barrier);
+
+/* barrier attribute functions */
+extern int pthread_barrierattr_destroy(pthread_barrierattr_t *attr);
+extern int pthread_barrierattr_getpshared(const pthread_barrierattr_t *attr,
+	int *shared);
+extern int pthread_barrierattr_init(pthread_barrierattr_t *attr);
+extern int pthread_barrierattr_setpshared(pthread_barrierattr_t *attr,
+	int shared);
+
 /* condition variable functions */
 extern int pthread_cond_destroy(pthread_cond_t *cond);
 extern int pthread_cond_init(pthread_cond_t *cond,

headers/posix/sys/types.h

@@ -60,6 +60,8 @@ typedef struct __timer_t*	timer_t;
 
 typedef struct	_pthread_thread		*pthread_t;
 typedef struct  _pthread_attr		*pthread_attr_t;
+typedef struct  _pthread_barrier	pthread_barrier_t;
+typedef struct  _pthread_barrierattr	*pthread_barrierattr_t;
 typedef struct  _pthread_mutex		pthread_mutex_t;
 typedef struct  _pthread_mutexattr	*pthread_mutexattr_t;
 typedef struct  _pthread_cond		pthread_cond_t;
@@ -69,10 +71,6 @@ typedef struct  _pthread_once		pthread_once_t;
 typedef struct  _pthread_rwlock		pthread_rwlock_t;
 typedef struct  _pthread_rwlockattr	*pthread_rwlockattr_t;
 typedef struct  _pthread_spinlock	pthread_spinlock_t;
-/*
-typedef struct  _pthread_barrier	*pthread_barrier_t;
-typedef struct  _pthread_barrierattr *pthread_barrierattr_t;
-*/
 
 struct _pthread_mutex {
 	__haiku_std_uint32	flags;
@@ -82,6 +80,14 @@ struct _pthread_mutex {
 	__haiku_std_int32	owner_count;
 };
 
+struct _pthread_barrier {
+	__haiku_std_uint32	flags;
+	__haiku_std_int32	lock;
+	__haiku_std_int32	mutex;
+	__haiku_std_int32	waiter_count;
+	__haiku_std_int32	waiter_max;
+};
+
 struct _pthread_cond {
 	__haiku_std_uint32	flags;
 	__haiku_std_int32	unused;

headers/private/libroot/pthread_private.h

@@ -37,6 +37,10 @@ typedef struct _pthread_mutexattr {
 	bool		process_shared;
 } pthread_mutexattr;
 
+typedef struct _pthread_barrierattr {
+	bool		process_shared;
+} pthread_barrierattr;
+
 typedef struct _pthread_attr {
 	int32		detach_state;
 	int32		sched_priority;

src/system/libroot/posix/pthread/Jamfile

@@ -15,6 +15,7 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 			pthread.cpp
 			pthread_atfork.c
 			pthread_attr.c
+			pthread_barrier.cpp
 			pthread_cancel.cpp
 			pthread_cleanup.cpp
 			pthread_cond.cpp

src/system/libroot/posix/pthread/pthread_barrier.cpp

@@ -0,0 +1,157 @@
+/*
+ * Copyright 2016, Dmytro Shynkevych, [email protected]
+ * Distributed under the terms of the MIT license.
+ */
+
+
+#include <pthread.h>
+#include "pthread_private.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <syscall_utils.h>
+#include <syscalls.h>
+#include <user_mutex_defs.h>
+
+
+#define BARRIER_FLAG_SHARED	0x80000000
+
+
+static const pthread_barrierattr pthread_barrierattr_default = {
+	/* .process_shared = */ false
+};
+
+
+int
+pthread_barrier_init(pthread_barrier_t* barrier,
+	const pthread_barrierattr_t* _attr, unsigned count)
+{
+	const pthread_barrierattr* attr = _attr != NULL
+		? *_attr : &pthread_barrierattr_default;
+
+	if (barrier == NULL || attr == NULL || count < 1)
+		return B_BAD_VALUE;
+
+	barrier->flags = attr->process_shared ? BARRIER_FLAG_SHARED : 0;
+	barrier->lock = 0;
+	barrier->mutex = 0;
+	barrier->waiter_count = 0;
+	barrier->waiter_max = count;
+
+	return B_OK;
+}
+
+
+int
+pthread_barrier_wait(pthread_barrier_t* barrier)
+{
+	if (barrier == NULL)
+		return B_BAD_VALUE;
+
+	// Enter critical region: lock the mutex
+	int32 status = atomic_or((int32*)&barrier->mutex, B_USER_MUTEX_LOCKED);
+
+	// If already locked, call the kernel
+	if (status & (B_USER_MUTEX_LOCKED | B_USER_MUTEX_WAITING)) {
+		do {
+			status = _kern_mutex_lock((int32*)&barrier->mutex, NULL, 0, 0);
+		} while (status == B_INTERRUPTED);
+
+		if (status != B_OK)
+			return status;
+	}
+
+	barrier->waiter_count++;
+
+	// If this thread is the last to arrive
+	if (barrier->waiter_count == barrier->waiter_max) {
+		// Let other threads exit the do...while loop
+		barrier->waiter_count = 0;
+
+		// Wake up everyone trying to acquire the barrier lock
+		_kern_mutex_unlock((int32*)&barrier->lock, B_USER_MUTEX_UNBLOCK_ALL);
+
+		// Exit critical region: unlock the mutex
+		int32 status = atomic_and((int32*)&barrier->mutex,
+				~(int32)B_USER_MUTEX_LOCKED);
+
+		if (status & B_USER_MUTEX_WAITING)
+			_kern_mutex_unlock((int32*)&barrier->mutex, 0);
+
+		// Inform the calling thread that it arrived last
+		return PTHREAD_BARRIER_SERIAL_THREAD;
+	}
+
+	do {
+		// Wait indefinitely trying to acquire the barrier lock.
+		// Other threads may now enter (mutex is unlocked).
+		_kern_mutex_switch_lock((int32*)&barrier->mutex,
+				(int32*)&barrier->lock, "barrier wait", 0, 0);
+	} while (barrier->waiter_count != 0);
+
+	// This thread did not arrive last
+	return 0;
+}
+
+
+int
+pthread_barrier_destroy(pthread_barrier_t* barrier)
+{
+	// No dynamic resources to free
+	return B_OK;
+}
+
+
+int
+pthread_barrierattr_init(pthread_barrierattr_t* _attr)
+{
+	pthread_barrierattr* attr = (pthread_barrierattr*)malloc(
+		sizeof(pthread_barrierattr));
+
+	if (attr == NULL)
+		return B_NO_MEMORY;
+
+	*attr = pthread_barrierattr_default;
+	*_attr = attr;
+
+	return B_OK;
+}
+
+
+int
+pthread_barrierattr_destroy(pthread_barrierattr_t* _attr)
+{
+	pthread_barrierattr* attr = _attr != NULL ? *_attr : NULL;
+
+	if (attr == NULL)
+		return B_BAD_VALUE;
+
+	free(attr);
+
+	return B_OK;
+}
+
+
+int
+pthread_barrierattr_getpshared(const pthread_barrierattr_t* _attr, int* shared)
+{
+	pthread_barrierattr* attr = *_attr;
+
+	*shared = attr->process_shared
+		? PTHREAD_PROCESS_SHARED : PTHREAD_PROCESS_PRIVATE;
+
+	return B_OK;
+}
+
+
+int
+pthread_barrierattr_setpshared(pthread_barrierattr_t* _attr, int shared)
+{
+	pthread_barrierattr* attr = *_attr;
+
+	attr->process_shared = shared == PTHREAD_PROCESS_SHARED;
+
+	return 0;
+}

src/tests/system/libroot/posix/Jamfile

@@ -37,6 +37,7 @@ SimpleTest tst-mktime : tst-mktime.c ;
 SimpleTest <test>truncate : truncate.cpp ;
 SimpleTest init_rld_after_fork_test : init_rld_after_fork_test.cpp ;
 SimpleTest user_thread_fork_test : user_thread_fork_test.cpp ;
+SimpleTest pthread_barrier_test : pthread_barrier_test.cpp ;
 
 # XSI tests
 SimpleTest xsi_msg_queue_test1 : xsi_msg_queue_test1.cpp ;

src/tests/system/libroot/posix/pthread_barrier_test.cpp

@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <pthread.h>
+
+#define THREAD_COUNT 10
+#define CYCLES 2
+
+pthread_barrier_t mybarrier;
+
+void* threadFn(void* id_ptr)
+{
+	int thread_id = *(int*)id_ptr;
+
+	for (int i = 0; i < CYCLES; ++i) {
+		int wait_sec = 1 + rand() % 10;
+		printf("thread %d: Wait %d seconds.\n", thread_id, wait_sec);
+		sleep(wait_sec);
+		printf("thread %d: Waiting on barrier...\n", thread_id);
+
+		int status = pthread_barrier_wait(&mybarrier);
+		if (status == PTHREAD_BARRIER_SERIAL_THREAD)
+			printf("thread %d: serial thread.\n", thread_id);
+		printf("thread %d: Finished!\n", thread_id);
+	}
+
+	return NULL;
+}
+
+
+int main()
+{
+	pthread_t ids[THREAD_COUNT];
+	int short_ids[THREAD_COUNT];
+
+	srand(time(NULL));
+	pthread_barrier_init(&mybarrier, NULL, THREAD_COUNT);
+
+	for (int i = 0; i < THREAD_COUNT; i++) {
+		short_ids[i] = i;
+		pthread_create(&ids[i], NULL, threadFn, &short_ids[i]);
+	}
+
+	for (int i = 0; i < THREAD_COUNT; i++)
+		pthread_join(ids[i], NULL);
+
+	pthread_barrier_destroy(&mybarrier);
+
+	return 0;
+}
+