Implement mutex_arc and rw_arc; add some tests

Author: bblum

src/libstd/arc.rs

@@ -5,8 +5,10 @@
 
 import unsafe::{shared_mutable_state, clone_shared_mutable_state,
                 get_shared_mutable_state, get_shared_immutable_state};
+import sync::{condvar, mutex, rwlock};
 
 export arc, clone, get;
+export mutex_arc, rw_arc;
 
 /****************************************************************************
  * Immutable ARC
@@ -43,10 +45,181 @@ fn clone<T: const send>(rc: &arc<T>) -> arc<T> {
  * Mutex protected ARC (unsafe)
  ****************************************************************************/
 
+struct mutex_arc_inner<T: send> { lock: mutex; failed: bool; data: T; }
+/// An ARC with mutable data protected by a blocking mutex.
+struct mutex_arc<T: send> { x: shared_mutable_state<mutex_arc_inner<T>>; }
+
+/// Create a mutex-protected ARC with the supplied data.
+fn mutex_arc<T: send>(+user_data: T) -> mutex_arc<T> {
+    let data = mutex_arc_inner {
+        lock: mutex(), failed: false, data: user_data
+    };
+    mutex_arc { x: unsafe { shared_mutable_state(data) } }
+}
+
+impl<T: send> &mutex_arc<T> {
+    /// Duplicate a mutex-protected ARC, as arc::clone.
+    fn clone() -> mutex_arc<T> {
+        // NB: Cloning the underlying mutex is not necessary. Its reference
+        // count would be exactly the same as the shared state's.
+        mutex_arc { x: unsafe { clone_shared_mutable_state(&self.x) } }
+    }
+
+    /**
+     * Access the underlying mutable data with mutual exclusion from other
+     * tasks. The argument closure will be run with the mutex locked; all
+     * other tasks wishing to access the data will block until the closure
+     * finishes running.
+     *
+     * The reason this function is 'unsafe' is because it is possible to
+     * construct a circular reference among multiple ARCs by mutating the
+     * underlying data. This creates potential for deadlock, but worse, this
+     * will guarantee a memory leak of all involved ARCs. Using mutex ARCs
+     * inside of other ARCs is safe in absence of circular references.
+     *
+     * If you wish to nest mutex_arcs, one strategy for ensuring safety at
+     * runtime is to add a "nesting level counter" inside the stored data, and
+     * when traversing the arcs, assert that they monotonically decrease.
+     *
+     * # Failure
+     *
+     * Failing while inside the ARC will unlock the ARC while unwinding, so
+     * that other tasks won't block forever. It will also poison the ARC:
+     * any tasks that subsequently try to access it (including those already
+     * blocked on the mutex) will also fail immediately.
+     */
+    #[inline(always)]
+    unsafe fn access<U>(blk: fn(x: &mut T) -> U) -> U {
+        let state = unsafe { get_shared_mutable_state(&self.x) };
+        // Borrowck would complain about this if the function were not already
+        // unsafe. See borrow_rwlock, far below.
+        do (&state.lock).lock {
+            check_poison(true, state.failed);
+            state.failed = true;
+            let result = blk(&mut state.data);
+            state.failed = false;
+            result
+        }
+    }
+/* FIXME(#3145): Make this compile; borrowck doesn't like it..?
+    /// As access(), but with a condvar, as sync::mutex.lock_cond().
+    #[inline(always)]
+    unsafe fn access_cond<U>(blk: fn(x: &mut T, condvar) -> U) -> U {
+        let state = unsafe { get_shared_mutable_state(&self.x) };
+        do (&state.lock).lock_cond |cond| {
+            check_poison(true, state.failed);
+            state.failed = true;
+            let result = blk(&mut state.data, cond);
+            state.failed = false;
+            result
+        }
+    }
+*/
+}
+
+// Common code for {mutex.access,rwlock.write}{,_cond}.
+#[inline(always)]
+fn check_poison(is_mutex: bool, failed: bool) {
+    if failed {
+        if is_mutex {
+            fail ~"Poisoned mutex_arc - another task failed inside!";
+        } else {
+            fail ~"Poisoned rw_arc - another task failed inside!";
+        }
+    }
+}
+
 /****************************************************************************
  * R/W lock protected ARC
  ****************************************************************************/
 
+struct rw_arc_inner<T: const send> { lock: rwlock; failed: bool; data: T; }
+/**
+ * A dual-mode ARC protected by a reader-writer lock. The data can be accessed
+ * mutably or immutably, and immutably-accessing tasks may run concurrently.
+ *
+ * Unlike mutex_arcs, rw_arcs are safe, because they cannot be nested.
+ */
+struct rw_arc<T: const send> {
+    x: shared_mutable_state<rw_arc_inner<T>>;
+    mut cant_nest: ();
+}
+
+/// Create a reader/writer ARC with the supplied data.
+fn rw_arc<T: const send>(+user_data: T) -> rw_arc<T> {
+    let data = rw_arc_inner {
+        lock: rwlock(), failed: false, data: user_data
+    };
+    rw_arc { x: unsafe { shared_mutable_state(data) }, cant_nest: () }
+}
+
+impl<T: const send> &rw_arc<T> {
+    /// Duplicate a rwlock-protected ARC, as arc::clone.
+    fn clone() -> rw_arc<T> {
+        rw_arc { x: unsafe { clone_shared_mutable_state(&self.x) },
+                 cant_nest: () }
+    }
+
+    /**
+     * Access the underlying data mutably. Locks the rwlock in write mode;
+     * other readers and writers will block.
+     *
+     * # Failure
+     *
+     * Failing while inside the ARC will unlock the ARC while unwinding, so
+     * that other tasks won't block forever. As mutex_arc.access, it will also
+     * poison the ARC, so subsequent readers and writers will both also fail.
+     */
+    #[inline(always)]
+    fn write<U>(blk: fn(x: &mut T) -> U) -> U {
+        let state = unsafe { get_shared_mutable_state(&self.x) };
+        do borrow_rwlock(state).write {
+            check_poison(false, state.failed);
+            state.failed = true;
+            let result = blk(&mut state.data);
+            state.failed = false;
+            result
+        }
+    }
+/* FIXME(#3145): Make this compile; borrowck doesn't like it..?
+    /// As write(), but with a condvar, as sync::rwlock.write_cond().
+    #[inline(always)]
+    fn write_cond<U>(blk: fn(x: &mut T, condvar) -> U) -> U {
+        let state = unsafe { get_shared_mutable_state(&self.x) };
+        do borrow_rwlock(state).write_cond |cond| {
+            check_poison(false, state.failed);
+            state.failed = true;
+            let result = blk(&mut state.data, cond);
+            state.failed = false;
+            result
+        }
+    }
+*/
+    /**
+     * Access the underlying data immutably. May run concurrently with other
+     * reading tasks.
+     *
+     * # Failure
+     *
+     * Failing will unlock the ARC while unwinding. However, unlike all other
+     * access modes, this will not poison the ARC.
+     */
+    fn read<U>(blk: fn(x: &T) -> U) -> U {
+        let state = unsafe { get_shared_immutable_state(&self.x) };
+        do (&state.lock).read {
+            check_poison(false, state.failed);
+            blk(&state.data)
+        }
+    }
+}
+
+// Borrowck rightly complains about immutably aliasing the rwlock in order to
+// lock it. This wraps the unsafety, with the justification that the 'lock'
+// field is never overwritten; only 'failed' and 'data'.
+fn borrow_rwlock<T: const send>(state: &mut rw_arc_inner<T>) -> &rwlock {
+    unsafe { unsafe::reinterpret_cast(&state.lock) }
+}
+
 /****************************************************************************
  * Tests
  ****************************************************************************/
@@ -80,4 +253,104 @@ mod tests {
 
         log(info, arc_v);
     }
+
+    #[test] #[should_fail] #[ignore(cfg(windows))]
+    fn test_mutex_arc_poison() {
+        let arc = ~mutex_arc(1);
+        let arc2 = ~arc.clone();
+        do task::try {
+            do arc2.access |one| {
+                assert *one == 2;
+            }
+        };
+        do arc.access |one| {
+            assert *one == 1;
+        }
+    }
+    #[test] #[should_fail] #[ignore(cfg(windows))]
+    fn test_rw_arc_poison_wr() {
+        let arc = ~rw_arc(1);
+        let arc2 = ~arc.clone();
+        do task::try {
+            do arc2.write |one| {
+                assert *one == 2;
+            }
+        };
+        do arc.read |one| {
+            assert *one == 1;
+        }
+    }
+    #[test] #[should_fail] #[ignore(cfg(windows))]
+    fn test_rw_arc_poison_ww() {
+        let arc = ~rw_arc(1);
+        let arc2 = ~arc.clone();
+        do task::try {
+            do arc2.write |one| {
+                assert *one == 2;
+            }
+        };
+        do arc.write |one| {
+            assert *one == 1;
+        }
+    }
+    #[test] #[ignore(cfg(windows))]
+    fn test_rw_arc_no_poison_rr() {
+        let arc = ~rw_arc(1);
+        let arc2 = ~arc.clone();
+        do task::try {
+            do arc2.read |one| {
+                assert *one == 2;
+            }
+        };
+        do arc.read |one| {
+            assert *one == 1;
+        }
+    }
+    #[test] #[ignore(cfg(windows))]
+    fn test_rw_arc_no_poison_rw() {
+        let arc = ~rw_arc(1);
+        let arc2 = ~arc.clone();
+        do task::try {
+            do arc2.read |one| {
+                assert *one == 2;
+            }
+        };
+        do arc.write |one| {
+            assert *one == 1;
+        }
+    }
+
+    #[test]
+    fn test_rw_arc() {
+        let arc = ~rw_arc(0);
+        let arc2 = ~arc.clone();
+        let (c,p) = pipes::stream();
+
+        do task::spawn {
+            do arc2.write |num| {
+                for 10.times {
+                    let tmp = *num;
+                    *num = -1;
+                    task::yield();
+                    *num = tmp + 1;
+                }
+                c.send(());
+            }
+        }
+        // Readers try to catch the writer in the act
+        let mut children = ~[];
+        for 5.times {
+            let arc3 = ~arc.clone();
+            do task::task().future_result(|+r| vec::push(children, r)).spawn {
+                do arc3.read |num| {
+                    assert *num >= 0;
+                }
+            }
+        }
+        // Wait for children to pass their asserts
+        for vec::each(children) |r| { future::get(r); }
+        // Wait for writer to finish
+        p.recv();
+        do arc.read |num| { assert *num == 10; }
+    }
 }

src/libstd/std.rc

@@ -18,6 +18,7 @@ import core::*;
 export net, net_tcp, net_ip, net_url;
 export uv, uv_ll, uv_iotask, uv_global_loop;
 export c_vec, timer;
+export sync, arc;
 export bitv, deque, fun_treemap, list, map;
 export smallintmap, sort, treemap;
 export rope, arena, par;