libc: pthread: implement mutexes

lib/libc/pthread/include/pthread.h

@@ -3,7 +3,9 @@
 
 #include <magenta/types.h>
 
-#define __PTHREAD_ATTR_SIZE__ 32
+#define __PTHREAD_ATTR_SIZE__     32
+
+#define PTHREAD_MUTEX_INITIALIZER ((pthread_mutex_t) {.__v = 0})
 
 typedef struct __pthread *pthread_t;
 
@@ -28,4 +30,8 @@ extern int pthread_join(pthread_t thread, void **retval);
 extern int pthread_detach(pthread_t thread);
 extern void pthread_exit(void *retval);
 
+extern int pthread_mutex_lock(pthread_mutex_t *mut);
+extern int pthread_mutex_trylock(pthread_mutex_t *mut);
+extern int pthread_mutex_unlock(pthread_mutex_t *mut);
+
 #endif

lib/libc/pthread/mutex/pthread_mutex_lock.c

@@ -0,0 +1,24 @@
+#include <errno.h>
+#include <magenta/futex.h>
+#include <pthread.h>
+
+int pthread_mutex_lock(pthread_mutex_t *mut)
+{
+	kern_futex_t expected = 0;
+	while (1) {
+		expected = 0;
+		if (__atomic_compare_exchange_n(
+			    &mut->__v,
+			    &expected,
+			    1,
+			    0,
+			    __ATOMIC_ACQUIRE,
+			    __ATOMIC_ACQUIRE)) {
+			return 0;
+		}
+
+		futex_wait(&mut->__v, 1, FUTEX_PRIVATE);
+	}
+
+	return __set_errno(EAGAIN);
+}

lib/libc/pthread/mutex/pthread_mutex_trylock.c

@@ -0,0 +1,18 @@
+#include <errno.h>
+#include <pthread.h>
+
+int pthread_mutex_trylock(pthread_mutex_t *mut)
+{
+	kern_futex_t expected = 0;
+	if (__atomic_compare_exchange_n(
+		    &mut->__v,
+		    &expected,
+		    1,
+		    0,
+		    __ATOMIC_ACQUIRE,
+		    __ATOMIC_ACQUIRE)) {
+		return 0;
+	}
+
+	return __set_errno(EBUSY);
+}

lib/libc/pthread/mutex/pthread_mutex_unlock.c

@@ -0,0 +1,8 @@
+#include <magenta/futex.h>
+#include <pthread.h>
+
+int pthread_mutex_unlock(pthread_mutex_t *mut)
+{
+	mut->__v = 0;
+	futex_wake(&mut->__v, 1, FUTEX_PRIVATE);
+}