Disconnect ports before draining them. Issue #1155

Author: brson

src/lib/comm.rs

@@ -45,6 +45,7 @@ native mod rustrt {
 
     fn new_port(unit_sz: uint) -> *rust_port;
     fn del_port(po: *rust_port);
+    fn rust_port_detach(po: *rust_port);
     fn get_port_id(po: *rust_port) -> port_id;
     fn rust_port_size(po: *rust_port) -> ctypes::size_t;
 }
@@ -79,6 +80,9 @@ tag chan<uniq T> {
 }
 
 resource port_ptr<uniq T>(po: *rustrt::rust_port) {
+    // Once the port is detached it's guaranteed not to receive further
+    // messages
+    rustrt::rust_port_detach(po);
     // Drain the port so that all the still-enqueued items get dropped
     while rustrt::rust_port_size(po) > 0u {
         // FIXME: For some reason if we don't assign to something here

src/rt/rust_builtin.cpp

@@ -467,11 +467,24 @@ new_port(size_t unit_sz) {
     return new (task->kernel, "rust_port") rust_port(task, unit_sz);
 }
 
+extern "C" CDECL void
+rust_port_detach(rust_port *port) {
+    rust_task *task = rust_scheduler::get_task();
+    LOG(task, comm, "rust_port_detach(0x%" PRIxPTR ")", (uintptr_t) port);
+    port->detach();
+    // FIXME: Busy waiting until we're the only ref
+    bool done = false;
+    while (!done) {
+        scoped_lock with(port->lock);
+        done = port->ref_count == 1;
+    }
+}
+
 extern "C" CDECL void
 del_port(rust_port *port) {
     rust_task *task = rust_scheduler::get_task();
     LOG(task, comm, "del_port(0x%" PRIxPTR ")", (uintptr_t) port);
-    scoped_lock with(task->lock);
+    A(task->sched, port->ref_count == 1, "Expected port ref_count == 1");
     port->deref();
 }
 

src/rt/rust_port.cpp

@@ -17,10 +17,17 @@ rust_port::rust_port(rust_task *task, size_t unit_sz)
 rust_port::~rust_port() {
     LOG(task, comm, "~rust_port 0x%" PRIxPTR, (uintptr_t) this);
 
-    task->release_port(id);
     task->deref();
 }
 
+void rust_port::detach() {
+    I(task->sched, !task->lock.lock_held_by_current_thread());
+    scoped_lock with(task->lock);
+    {
+        task->release_port(id);
+    }
+}
+
 void rust_port::send(void *sptr) {
     I(task->sched, !lock.lock_held_by_current_thread());
     scoped_lock with(lock);

src/rt/rust_port.h

@@ -20,6 +20,7 @@ class rust_port : public kernel_owned<rust_port>, public rust_cond {
     void send(void *sptr);
     bool receive(void *dptr);
     size_t size();
+    void detach();
 };
 
 //

src/rt/rustrt.def.in

@@ -34,6 +34,7 @@ rust_get_stdout
 rust_get_stderr
 rust_str_push
 rust_list_files
+rust_port_detach
 rust_port_size
 rust_process_wait
 rust_ptr_eq

src/test/run-pass/task-comm-chan-cleanup4.rs

@@ -0,0 +1,27 @@
+use std;
+import std::int;
+import std::comm;
+import std::task;
+
+// We're trying to trigger a race between send and port destruction that
+// results in the string not being freed
+
+fn starship(&&ch: std::comm::chan<str>) {
+    int::range(0, 10) { |_i|
+        comm::send(ch, "pew pew");
+    }
+}
+
+fn starbase(&&_args: ()) {
+    int::range(0, 10) { |_i|
+        let p = comm::port();
+        task::spawn(comm::chan(p), starship);
+        task::yield();
+    }
+}
+
+fn main() {
+    int::range(0, 10) { |_i|
+        task::spawn((), starbase);
+    }
+}