Remove rt::bookkeeping

This commit removes the runtime bookkeeping previously used to ensure
that all Rust tasks were joined before the runtime was shut down.

This functionality will be replaced by an RAII style `Thread` API, that
will also offer a detached mode.

Since this changes the semantics of shutdown, it is a:

[breaking-change]

src/libstd/rt/mod.rs

@@ -73,7 +73,6 @@ pub mod mutex;
 pub mod thread;
 pub mod exclusive;
 pub mod util;
-pub mod bookkeeping;
 pub mod local;
 pub mod task;
 pub mod unwind;
@@ -207,7 +206,6 @@ pub fn at_exit(f: proc():Send) {
 /// Invoking cleanup while portions of the runtime are still in use may cause
 /// undefined behavior.
 pub unsafe fn cleanup() {
-    bookkeeping::wait_for_other_tasks();
     args::cleanup();
     thread::cleanup();
     local_ptr::cleanup();

src/libstd/rt/task.rs

@@ -29,7 +29,6 @@ use str::SendStr;
 use thunk::Thunk;
 
 use rt;
-use rt::bookkeeping;
 use rt::mutex::NativeMutex;
 use rt::local::Local;
 use rt::thread::{mod, Thread};
@@ -132,11 +131,6 @@ impl Task {
 
         let stack = stack_size.unwrap_or(rt::min_stack());
 
-        // Note that this increment must happen *before* the spawn in order to
-        // guarantee that if this task exits it will always end up waiting for
-        // the spawned task to exit.
-        let token = bookkeeping::increment();
-
         // Spawning a new OS thread guarantees that __morestack will never get
         // triggered, but we must manually set up the actual stack bounds once
         // this function starts executing. This raises the lower limit by a bit
@@ -156,7 +150,6 @@ impl Task {
 
             let mut f = Some(f);
             drop(task.run(|| { f.take().unwrap().invoke(()) }).destroy());
-            drop(token);
         })
     }
 

src/libstd/sys/common/helper_thread.rs

@@ -25,7 +25,7 @@ use prelude::*;
 use cell::UnsafeCell;
 use mem;
 use sync::{StaticMutex, StaticCondvar};
-use rt::{mod, bookkeeping};
+use rt;
 use sys::helper_signal;
 
 use task;
@@ -83,7 +83,6 @@ impl<M: Send> Helper<M> {
 
                 let t = f();
                 task::spawn(move |:| {
-                    bookkeeping::decrement();
                     helper(receive, rx, t);
                     let _g = self.lock.lock();
                     *self.shutdown.get() = true;