Changeset 45c8eea in mainline for uspace/lib/c/generic/private/futex.h

Timestamp:

2018-11-11T15:47:39Z (5 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

f4cb6c5f

Parents:

269bc459

git-author:

Jakub Jermar <jakub@…> (2018-11-10 17:49:44)

git-committer:

Jakub Jermar <jakub@…> (2018-11-11 15:47:39)

Message:

Preallocate waitq handle during initialization

Do not clutter futex_down_composable() with the preallocation of the
wait queue handle and do it single-threadedly in futex_initialize().

File:

• uspace/lib/c/generic/private/futex.h (modified) (6 diffs)

uspace/lib/c/generic/private/futex.h

@@ -46 +46 @@
 typedef struct futex {
         volatile atomic_int val;
-        volatile atomic_int lock;
         volatile cap_waitq_handle_t whandle;
 
@@ -54 +53 @@
 } futex_t;
 
-extern void futex_initialize(futex_t *futex, int value);
+extern errno_t futex_initialize(futex_t *futex, int value);
 
 static inline errno_t futex_destroy(futex_t *futex)
@@ -64 +63 @@
 
 #ifdef CONFIG_DEBUG_FUTEX
-
-#define FUTEX_INITIALIZE(val) { (val), 0, CAP_NIL, NULL }
-#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
 
 void __futex_assert_is_locked(futex_t *, const char *);
@@ -85 +81 @@
 #else
 
-#define FUTEX_INITIALIZE(val) { (val), 0, CAP_NIL }
-#define FUTEX_INITIALIZER     FUTEX_INITIALIZE(1)
-
 #define futex_lock(fut)     (void) futex_down((fut))
 #define futex_trylock(fut)  futex_trydown((fut))
@@ -98 +91 @@
 #endif
 
-static errno_t allocate_waitq(futex_t *futex)
-{
-        int expected = 0;
-        while (!atomic_compare_exchange_weak_explicit(&futex->lock, &expected,
-            1, memory_order_acquire, memory_order_relaxed))
-                expected = 0;
-
-        if (futex->whandle == CAP_NIL) {
-                errno_t rc = __SYSCALL1(SYS_WAITQ_CREATE,
-                    (sysarg_t) &futex->whandle);
-                if (rc != EOK) {
-                        atomic_store_explicit(&futex->lock, 0,
-                            memory_order_release);
-                        return rc;
-                }
-        }
-
-        atomic_store_explicit(&futex->lock, 0, memory_order_release);
-        return EOK;
+static inline errno_t futex_allocate_waitq(futex_t *futex)
+{
+        return __SYSCALL1(SYS_WAITQ_CREATE, (sysarg_t) &futex->whandle);
 }
 
@@ -140 +117 @@
         // TODO: Add tests for this.
 
-        // Preallocate the waitq handle so that we don't need to risk a failure
-        // during wakeup
-        if (futex->whandle == CAP_NIL) {
-                errno_t rc = allocate_waitq(futex);
-                if (rc != EOK)
-                        return rc;
-        }
+        assert(futex->whandle != CAP_NIL);
 
         if (atomic_fetch_sub_explicit(&futex->val, 1, memory_order_acquire) > 0)