Changes in uspace/lib/c/include/futex.h [a35b458:b59318e] in mainline

File:

• uspace/lib/c/include/futex.h (modified) (4 diffs)

uspace/lib/c/include/futex.h

@@ -36 +36 @@
 #define LIBC_FUTEX_H_
 
+#include <assert.h>
 #include <atomic.h>
 #include <errno.h>
 #include <libc.h>
+#include <time.h>
 
 typedef struct futex {
         atomic_t val;
-#ifdef FUTEX_UPGRADABLE
-        int upgraded;
+#ifdef CONFIG_DEBUG_FUTEX
+        _Atomic void *owner;
 #endif
 } futex_t;
 
-
 extern void futex_initialize(futex_t *futex, int value);
 
-#ifdef FUTEX_UPGRADABLE
-#include <rcu.h>
+#ifdef CONFIG_DEBUG_FUTEX
 
-#define FUTEX_INITIALIZE(val) {{ (val) }, 0}
+#define FUTEX_INITIALIZE(val) {{ (val) }, NULL }
+#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
 
-#define futex_lock(fut) \
-({ \
-        rcu_read_lock(); \
-        (fut)->upgraded = rcu_access(_upgrade_futexes); \
-        if ((fut)->upgraded) \
-                (void) futex_down((fut)); \
-})
+void __futex_assert_is_locked(futex_t *, const char *);
+void __futex_assert_is_not_locked(futex_t *, const char *);
+void __futex_lock(futex_t *, const char *);
+void __futex_unlock(futex_t *, const char *);
+bool __futex_trylock(futex_t *, const char *);
+void __futex_give_to(futex_t *, void *, const char *);
 
-#define futex_trylock(fut) \
-({ \
-        rcu_read_lock(); \
-        int _upgraded = rcu_access(_upgrade_futexes); \
-        if (_upgraded) { \
-                int _acquired = futex_trydown((fut)); \
-                if (!_acquired) { \
-                        rcu_read_unlock(); \
-                } else { \
-                        (fut)->upgraded = true; \
-                } \
-                _acquired; \
-        } else { \
-                (fut)->upgraded = false; \
-                1; \
-        } \
-})
+#define futex_lock(futex) __futex_lock((futex), #futex)
+#define futex_unlock(futex) __futex_unlock((futex), #futex)
+#define futex_trylock(futex) __futex_trylock((futex), #futex)
 
-#define futex_unlock(fut) \
-({ \
-        if ((fut)->upgraded) \
-                (void) futex_up((fut)); \
-        rcu_read_unlock(); \
-})
-
-extern int _upgrade_futexes;
-
-extern void futex_upgrade_all_and_wait(void);
+#define futex_give_to(futex, new_owner) __futex_give_to((futex), (new_owner), #futex)
+#define futex_assert_is_locked(futex) __futex_assert_is_locked((futex), #futex)
+#define futex_assert_is_not_locked(futex) __futex_assert_is_not_locked((futex), #futex)
 
 #else
 
 #define FUTEX_INITIALIZE(val) {{ (val) }}
+#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
 
 #define futex_lock(fut)     (void) futex_down((fut))
@@ -100 +80 @@
 #define futex_unlock(fut)   (void) futex_up((fut))
 
+#define futex_give_to(fut, owner) ((void)0)
+#define futex_assert_is_locked(fut) assert((atomic_signed_t) (fut)->val.count <= 0)
+#define futex_assert_is_not_locked(fut) ((void)0)
+
 #endif
-
-#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
 
 /** Try to down the futex.
@@ -117 +99 @@
 }
 
-/** Down the futex.
+/** Down the futex with timeout, composably.
+ *
+ * This means that when the operation fails due to a timeout or being
+ * interrupted, the next futex_up() is ignored, which allows certain kinds of
+ * composition of synchronization primitives.
+ *
+ * In most other circumstances, regular futex_down_timeout() is a better choice.
  *
  * @param futex Futex.
  *
  * @return ENOENT if there is no such virtual address.
+ * @return ETIMEOUT if timeout expires.
  * @return EOK on success.
  * @return Error code from <errno.h> otherwise.
  *
  */
-static inline errno_t futex_down(futex_t *futex)
+static inline errno_t futex_down_composable(futex_t *futex, struct timeval *expires)
 {
+        // TODO: Add tests for this.
+
+        /* No timeout by default. */
+        suseconds_t timeout = 0;
+
+        if (expires) {
+                struct timeval tv;
+                getuptime(&tv);
+                if (tv_gteq(&tv, expires)) {
+                        /* We can't just return ETIMEOUT. That wouldn't be composable. */
+                        timeout = 1;
+                } else {
+                        timeout = tv_sub_diff(expires, &tv);
+                }
+
+                assert(timeout > 0);
+        }
+
         if ((atomic_signed_t) atomic_predec(&futex->val) < 0)
-                return (errno_t) __SYSCALL1(SYS_FUTEX_SLEEP, (sysarg_t) &futex->val.count);
+                return (errno_t) __SYSCALL2(SYS_FUTEX_SLEEP, (sysarg_t) &futex->val.count, (sysarg_t) timeout);
 
         return EOK;
@@ -151 +158 @@
 }
 
+static inline errno_t futex_down_timeout(futex_t *futex, struct timeval *expires)
+{
+        /*
+         * This combination of a "composable" sleep followed by futex_up() on
+         * failure is necessary to prevent breakage due to certain race
+         * conditions.
+         */
+        errno_t rc = futex_down_composable(futex, expires);
+        if (rc != EOK)
+                futex_up(futex);
+        return rc;
+}
+
+/** Down the futex.
+ *
+ * @param futex Futex.
+ *
+ * @return ENOENT if there is no such virtual address.
+ * @return EOK on success.
+ * @return Error code from <errno.h> otherwise.
+ *
+ */
+static inline errno_t futex_down(futex_t *futex)
+{
+        return futex_down_timeout(futex, NULL);
+}
+
 #endif