Changes in uspace/lib/c/include/futex.h [b59318e:a35b458] 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 CONFIG_DEBUG_FUTEX
-        _Atomic void *owner;
+#ifdef FUTEX_UPGRADABLE
+        int upgraded;
 #endif
 } futex_t;
 
+
 extern void futex_initialize(futex_t *futex, int value);
 
-#ifdef CONFIG_DEBUG_FUTEX
+#ifdef FUTEX_UPGRADABLE
+#include <rcu.h>
 
-#define FUTEX_INITIALIZE(val) {{ (val) }, NULL }
-#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
+#define FUTEX_INITIALIZE(val) {{ (val) }, 0}
 
-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_lock(fut) \
+({ \
+        rcu_read_lock(); \
+        (fut)->upgraded = rcu_access(_upgrade_futexes); \
+        if ((fut)->upgraded) \
+                (void) futex_down((fut)); \
+})
 
-#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_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_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)
+#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);
 
 #else
 
 #define FUTEX_INITIALIZE(val) {{ (val) }}
-#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
 
 #define futex_lock(fut)     (void) futex_down((fut))
@@ -80 +100 @@
 #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
 
-#endif
+#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
 
 /** Try to down the futex.
@@ -99 +117 @@
 }
 
-/** 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.
+/** Down the futex.
  *
  * @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_composable(futex_t *futex, struct timeval *expires)
+static inline errno_t futex_down(futex_t *futex)
 {
-        // 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) __SYSCALL2(SYS_FUTEX_SLEEP, (sysarg_t) &futex->val.count, (sysarg_t) timeout);
+                return (errno_t) __SYSCALL1(SYS_FUTEX_SLEEP, (sysarg_t) &futex->val.count);
 
         return EOK;
@@ -158 +151 @@
 }
 
-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