Add a real semaphore implemtation

I've seen races where job N+1 got started before N, this breaks
for dependent jobs. So give up and implement a real semaphore
in mmap'ed shared storage.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 85 insertions, 0 deletions

diff --git a/mutex.c b/mutex.c
new file mode 100644
index 00000000..bb417c27
--- /dev/null
+++ b/mutex.c
@@ -0,0 +1,85 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <sys/mman.h>
+
+#include "mutex.h"
+
+void fio_sem_remove(struct fio_sem *sem)
+{
+	unlink(sem->sem_name);
+	munmap(sem, sizeof(*sem));
+}
+
+struct fio_sem *fio_sem_init(int value)
+{
+	pthread_mutexattr_t attr;
+	struct fio_sem *sem;
+	char sem_name[32];
+	int fd;
+
+	sprintf(sem_name, "/tmp/.fio_lock.XXXXXX");
+	fd = mkstemp(sem_name);
+	if (fd < 0) {
+		perror("open sem");
+		return NULL;
+	}
+
+	if (ftruncate(fd, sizeof(struct fio_sem)) < 0) {
+		perror("ftruncate sem");
+		return NULL;
+	}
+
+	sem = mmap(NULL, sizeof(struct fio_sem), PROT_READ | PROT_WRITE,
+			MAP_SHARED, fd, 0);
+	if (sem == MAP_FAILED) {
+		perror("mmap sem");
+		close(fd);
+		unlink(sem_name);
+		return NULL;
+	}
+
+	close(fd);
+	sem->value = value;
+	strcpy(sem->sem_name, sem_name);
+
+	if (pthread_mutexattr_init(&attr)) {
+		perror("pthread_mutexattr_init");
+		goto err;
+	}
+	if (pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED)) {
+		perror("pthread_mutexattr_setpshared");
+		goto err;
+	}
+	if (pthread_mutex_init(&sem->lock, &attr)) {
+		perror("pthread_mutex_init");
+		goto err;
+	}
+
+	return sem;
+err:
+	munmap(sem, sizeof(*sem));
+	unlink(sem_name);
+	return NULL;
+}
+
+void fio_sem_down(struct fio_sem *sem)
+{
+	pthread_mutex_lock(&sem->lock);
+	while (sem->value == 0)
+		pthread_cond_wait(&sem->cond, &sem->lock);
+	sem->value--;
+	pthread_mutex_unlock(&sem->lock);
+}
+
+void fio_sem_up(struct fio_sem *sem)
+{
+	pthread_mutex_lock(&sem->lock);
+	if (!sem->value)
+		pthread_cond_signal(&sem->cond);
+	sem->value++;
+	pthread_mutex_unlock(&sem->lock);
+}