SGX target: implement synchronization primitives and threading

[rust.git] / src / libstd / sys_common / mutex.rs

diff --git a/src/libstd/sys_common/mutex.rs b/src/libstd/sys_common/mutex.rs
index d1a738770d3893fb66189c036009fd62375984db..87684237638987c805f1c3f7e7baf678a319376c 100644 (file)
--- a/src/libstd/sys_common/mutex.rs
+++ b/src/libstd/sys_common/mutex.rs
@@ -24,11 +24,18 @@ impl Mutex {
     ///
     /// Behavior is undefined if the mutex is moved after it is
     /// first used with any of the functions below.
+    /// Also, until `init` is called, behavior is undefined if this
+    /// mutex is ever used reentrantly, i.e., `raw_lock` or `try_lock`
+    /// are called by the thread currently holding the lock.
+    #[unstable(feature = "sys_internals", issue = "0")] // FIXME: min_const_fn
     pub const fn new() -> Mutex { Mutex(imp::Mutex::new()) }
 
     /// Prepare the mutex for use.
     ///
     /// This should be called once the mutex is at a stable memory address.
+    /// If called, this must be the very first thing that happens to the mutex.
+    /// Calling it in parallel with or after any operation (including another
+    /// `init()`) is undefined behavior.
     #[inline]
     pub unsafe fn init(&mut self) { self.0.init() }
 
@@ -37,7 +44,15 @@ pub unsafe fn init(&mut self) { self.0.init() }
     /// Behavior is undefined if the mutex has been moved between this and any
     /// previous function call.
     #[inline]
-    pub unsafe fn lock(&self) { self.0.lock() }
+    pub unsafe fn raw_lock(&self) { self.0.lock() }
+
+    /// Calls raw_lock() and then returns an RAII guard to guarantee the mutex
+    /// will be unlocked.
+    #[inline]
+    pub unsafe fn lock(&self) -> MutexGuard {
+        self.raw_lock();
+        MutexGuard(&self.0)
+    }
 
     /// Attempts to lock the mutex without blocking, returning whether it was
     /// successfully acquired or not.
@@ -51,8 +66,11 @@ pub unsafe fn try_lock(&self) -> bool { self.0.try_lock() }
     ///
     /// Behavior is undefined if the current thread does not actually hold the
     /// mutex.
+    ///
+    /// Consider switching from the pair of raw_lock() and raw_unlock() to
+    /// lock() whenever possible.
     #[inline]
-    pub unsafe fn unlock(&self) { self.0.unlock() }
+    pub unsafe fn raw_unlock(&self) { self.0.unlock() }
 
     /// Deallocates all resources associated with this mutex.
     ///
@@ -64,3 +82,14 @@ pub unsafe fn destroy(&self) { self.0.destroy() }
 
 // not meant to be exported to the outside world, just the containing module
 pub fn raw(mutex: &Mutex) -> &imp::Mutex { &mutex.0 }
+
+#[must_use]
+/// A simple RAII utility for the above Mutex without the poisoning semantics.
+pub struct MutexGuard<'a>(&'a imp::Mutex);
+
+impl<'a> Drop for MutexGuard<'a> {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe { self.0.unlock(); }
+    }
+}