diff --git a/src/libcore/comm.rs b/src/libcore/comm.rs
index 69fd09e618c..1a86ccf3671 100644
--- a/src/libcore/comm.rs
+++ b/src/libcore/comm.rs
@@ -37,8 +37,7 @@ enum rust_port {}
 
 #[abi = "cdecl"]
 native mod rustrt {
-    fn rust_port_id_send<T: send>(t: *sys::type_desc,
-                                  target_port: port_id,
+    fn rust_port_id_send<T: send>(target_port: port_id,
                                   data: T) -> libc::uintptr_t;
 
     fn new_port(unit_sz: libc::size_t) -> *rust_port;
@@ -114,7 +113,7 @@ whereupon the caller loses access to it.
 "]
 fn send<T: send>(ch: chan<T>, -data: T) {
     let chan_t(p) = ch;
-    let res = rustrt::rust_port_id_send(sys::get_type_desc::<T>(), p, data);
+    let res = rustrt::rust_port_id_send(p, data);
     if res != 0u unsafe {
         // Data sent successfully
         unsafe::forget(data);
diff --git a/src/libcore/priv.rs b/src/libcore/priv.rs
index ec432a69ef2..b8e0848dc87 100644
--- a/src/libcore/priv.rs
+++ b/src/libcore/priv.rs
@@ -4,10 +4,14 @@ export chan_from_global_ptr;
 
 import compare_and_swap = rustrt::rust_compare_and_swap_ptr;
 
+type rust_port_id = uint;
+
 native mod rustrt {
     fn rust_compare_and_swap_ptr(address: *libc::uintptr_t,
                                  oldval: libc::uintptr_t,
                                  newval: libc::uintptr_t) -> bool;
+    fn rust_task_weaken(ch: rust_port_id);
+    fn rust_task_unweaken(ch: rust_port_id);
 }
 
 type global_ptr<T: send> = *libc::uintptr_t;
@@ -143,3 +147,83 @@ fn test_from_global_chan2() unsafe {
         assert winners == 1u;
     }
 }
+
+#[doc = "
+Convert the current task to a 'weak' task temporarily
+
+As a weak task it will not be counted towards the runtime's set
+of live tasks. When there are no more outstanding live (non-weak) tasks
+the runtime will send an exit message on the provided channel.
+
+This function is super-unsafe. Do not use.
+
+# Safety notes
+
+* Weak tasks must either die on their own or exit upon receipt of
+  the exit message. Failure to do so will cause the runtime to never
+  exit
+* Tasks must not call `weaken_task` multiple times. This will
+  break the kernel's accounting of live tasks.
+* Weak tasks must not be supervised. A supervised task keeps
+  a reference to its parent, so the parent will not die.
+"]
+unsafe fn weaken_task(f: fn(comm::port<()>)) unsafe {
+    let po = comm::port();
+    let ch = comm::chan(po);
+    rustrt::rust_task_weaken(unsafe::reinterpret_cast(ch));
+    let _unweaken = unweaken(ch);
+    f(po);
+
+    resource unweaken(ch: comm::chan<()>) unsafe {
+        rustrt::rust_task_unweaken(unsafe::reinterpret_cast(ch));
+    }
+}
+
+#[test]
+fn test_weaken_task_then_unweaken() unsafe {
+    task::try {||
+        weaken_task {|_po|
+        }
+    };
+}
+
+#[test]
+fn test_weaken_task_wait() unsafe {
+    let builder = task::builder();
+    task::unsupervise(builder);
+    task::run(builder) {||
+        weaken_task {|po|
+            comm::recv(po);
+        }
+    }
+}
+
+#[test]
+fn test_weaken_task_stress() unsafe {
+    // Create a bunch of weak tasks
+    iter::repeat(100u) {||
+        task::spawn {||
+            weaken_task {|_po|
+            }
+        }
+        let builder = task::builder();
+        task::unsupervise(builder);
+        task::run(builder) {||
+            weaken_task {|po|
+                // Wait for it to tell us to die
+                comm::recv(po);
+            }
+        }
+    }
+}
+
+#[test]
+#[ignore(cfg(target_os = "win32"))]
+fn test_weaken_task_fail() unsafe {
+    let res = task::try {||
+        weaken_task {|_po|
+            fail;
+        }
+    };
+    assert result::is_failure(res);
+}
\ No newline at end of file
diff --git a/src/rt/rust_builtin.cpp b/src/rt/rust_builtin.cpp
index 910331fa7c0..f2714c4d7c3 100644
--- a/src/rt/rust_builtin.cpp
+++ b/src/rt/rust_builtin.cpp
@@ -669,22 +669,9 @@ get_port_id(rust_port *port) {
 }
 
 extern "C" CDECL uintptr_t
-rust_port_id_send(type_desc *t, rust_port_id target_port_id, void *sptr) {
-    bool sent = false;
+rust_port_id_send(rust_port_id target_port_id, void *sptr) {
     rust_task *task = rust_get_current_task();
-
-    LOG(task, comm, "rust_port_id*_send port: 0x%" PRIxPTR,
-        (uintptr_t) target_port_id);
-
-    rust_port *port = task->kernel->get_port_by_id(target_port_id);
-    if(port) {
-        port->send(sptr);
-        port->deref();
-        sent = true;
-    } else {
-        LOG(task, comm, "didn't get the port");
-    }
-    return (uintptr_t)sent;
+    return (uintptr_t)task->kernel->send_to_port(target_port_id, sptr);
 }
 
 // This is called by an intrinsic on the Rust stack and must run
@@ -782,6 +769,18 @@ rust_compare_and_swap_ptr(intptr_t *address,
     return sync::compare_and_swap(address, oldval, newval);
 }
 
+extern "C" CDECL void
+rust_task_weaken(rust_port_id chan) {
+    rust_task *task = rust_get_current_task();
+    task->kernel->weaken_task(chan);
+}
+
+extern "C" CDECL void
+rust_task_unweaken(rust_port_id chan) {
+    rust_task *task = rust_get_current_task();
+    task->kernel->unweaken_task(chan);
+}
+
 //
 // Local Variables:
 // mode: C++
diff --git a/src/rt/rust_kernel.cpp b/src/rt/rust_kernel.cpp
index ff6b0e1056c..21422646f0d 100644
--- a/src/rt/rust_kernel.cpp
+++ b/src/rt/rust_kernel.cpp
@@ -1,11 +1,11 @@
 
 
-
 #include "rust_kernel.h"
 #include "rust_port.h"
 #include "rust_util.h"
 #include "rust_scheduler.h"
 #include "rust_sched_launcher.h"
+#include <algorithm>
 
 #define KLOG_(...)                              \
     KLOG(this, kern, __VA_ARGS__)
@@ -21,6 +21,7 @@ rust_kernel::rust_kernel(rust_env *env) :
     max_sched_id(0),
     sched_reaper(this),
     osmain_driver(NULL),
+    non_weak_tasks(0),
     env(env)
 {
     // Create the single threaded scheduler that will run on the platform's
@@ -286,6 +287,84 @@ rust_kernel::set_exit_status(int code) {
     }
 }
 
+void
+rust_kernel::register_task() {
+    KLOG_("Registering task");
+    uintptr_t new_non_weak_tasks = sync::increment(non_weak_tasks);
+    KLOG_("New non-weak tasks %" PRIdPTR, new_non_weak_tasks);
+}
+
+void
+rust_kernel::unregister_task() {
+    KLOG_("Unregistering task");
+    uintptr_t new_non_weak_tasks = sync::decrement(non_weak_tasks);
+    KLOG_("New non-weak tasks %" PRIdPTR, new_non_weak_tasks);
+    if (new_non_weak_tasks == 0) {
+        end_weak_tasks();
+    }
+}
+
+void
+rust_kernel::weaken_task(rust_port_id chan) {
+    {
+        scoped_lock with(weak_task_lock);
+        KLOG_("Weakening task with channel %" PRIdPTR, chan);
+        weak_task_chans.push_back(chan);
+    }
+    uintptr_t new_non_weak_tasks = sync::decrement(non_weak_tasks);
+    KLOG_("New non-weak tasks %" PRIdPTR, new_non_weak_tasks);
+    if (new_non_weak_tasks == 0) {
+        end_weak_tasks();
+    }
+}
+
+void
+rust_kernel::unweaken_task(rust_port_id chan) {
+    uintptr_t new_non_weak_tasks = sync::increment(non_weak_tasks);
+    KLOG_("New non-weak tasks %" PRIdPTR, new_non_weak_tasks);
+    {
+        scoped_lock with(weak_task_lock);
+        KLOG_("Unweakening task with channel %" PRIdPTR, chan);
+        std::vector<rust_port_id>::iterator iter =
+            std::find(weak_task_chans.begin(), weak_task_chans.end(), chan);
+        if (iter != weak_task_chans.end()) {
+            weak_task_chans.erase(iter);
+        }
+    }
+}
+
+void
+rust_kernel::end_weak_tasks() {
+    std::vector<rust_port_id> chancopies;
+    {
+        //scoped_lock with(weak_task_lock);
+        chancopies = weak_task_chans;
+        weak_task_chans.clear();
+    }
+    while (!chancopies.empty()) {
+        rust_port_id chan = chancopies.back();
+        chancopies.pop_back();
+        KLOG_("Notifying weak task " PRIdPTR, chan);
+        uintptr_t token = 0;
+        send_to_port(chan, &token);
+    }
+}
+
+bool
+rust_kernel::send_to_port(rust_port_id chan, void *sptr) {
+    KLOG_("rust_port_id*_send port: 0x%" PRIxPTR, (uintptr_t) chan);
+
+    rust_port *port = get_port_by_id(chan);
+    if(port) {
+        port->send(sptr);
+        port->deref();
+        return true;
+    } else {
+        KLOG_("didn't get the port");
+        return false;
+    }
+}
+
 //
 // Local Variables:
 // mode: C++
diff --git a/src/rt/rust_kernel.h b/src/rt/rust_kernel.h
index 6a7a7070c20..1ccd423928d 100644
--- a/src/rt/rust_kernel.h
+++ b/src/rt/rust_kernel.h
@@ -63,7 +63,15 @@ class rust_kernel {
     // on the main thread
     rust_sched_driver *osmain_driver;
 
+    // An atomically updated count of the live, 'non-weak' tasks
+    uintptr_t non_weak_tasks;
+    // Protects weak_task_chans
+    lock_and_signal weak_task_lock;
+    // A list of weak tasks that need to be told when to exit
+    std::vector<rust_port_id> weak_task_chans;
+
     rust_scheduler* get_scheduler_by_id_nolock(rust_sched_id id);
+    void end_weak_tasks();
 
 public:
     struct rust_env *env;
@@ -102,6 +110,13 @@ public:
     void set_exit_status(int code);
 
     rust_sched_id osmain_sched_id() { return osmain_scheduler; }
+
+    void register_task();
+    void unregister_task();
+    void weaken_task(rust_port_id chan);
+    void unweaken_task(rust_port_id chan);
+
+    bool send_to_port(rust_port_id chan, void *sptr);
 };
 
 template <typename T> struct kernel_owned {
diff --git a/src/rt/rust_scheduler.cpp b/src/rt/rust_scheduler.cpp
index 1b5978b5cfe..1f0b16a1d58 100644
--- a/src/rt/rust_scheduler.cpp
+++ b/src/rt/rust_scheduler.cpp
@@ -92,6 +92,7 @@ rust_scheduler::create_task(rust_task *spawner, const char *name) {
         if (cur_thread >= num_threads)
             cur_thread = 0;
     }
+    kernel->register_task();
     rust_sched_launcher *thread = threads[thread_no];
     return thread->get_loop()->create_task(spawner, name);
 }
@@ -106,6 +107,7 @@ rust_scheduler::release_task() {
             need_exit = true;
         }
     }
+    kernel->unregister_task();
     if (need_exit) {
         exit();
     }
diff --git a/src/rt/rustrt.def.in b/src/rt/rustrt.def.in
index ec4f5bedb24..171718b64f2 100644
--- a/src/rt/rustrt.def.in
+++ b/src/rt/rustrt.def.in
@@ -54,6 +54,8 @@ rust_task_yield
 rust_task_is_unwinding
 rust_get_task
 rust_task_config_notify
+rust_task_weaken
+rust_task_unweaken
 sched_threads
 shape_log_str
 start_task