async-llvm(6): Make the LLVM work coordinator get its work package through a channel instead of upfront.

src/librustc_trans/back/write.rs

@@ -780,19 +780,31 @@ pub fn run_passes(sess: &Session,
 
     let (shared_emitter, shared_emitter_main) = SharedEmitter::new();
     let (trans_worker_send, trans_worker_receive) = channel();
+    let (coordinator_send, coordinator_receive) = channel();
 
     let coordinator_thread = start_executing_work(sess,
-                                                  work_items,
+                                                  work_items.len(),
                                                   shared_emitter,
                                                   trans_worker_send,
+                                                  coordinator_send.clone(),
+                                                  coordinator_receive,
                                                   client,
                                                   trans.exported_symbols.clone());
+    for work_item in work_items {
+        coordinator_send.send(Message::WorkItem(work_item)).unwrap();
+    }
+
     loop {
         shared_emitter_main.check(sess);
 
         match trans_worker_receive.recv() {
-            Ok(Message::AllWorkDone) |
-            Err(_) => break,
+            Err(_) => {
+                // An `Err` here means that all senders for this channel have
+                // been closed. This could happen because all work has
+                // completed successfully or there has been some error.
+                // At this point we don't care which it is.
+                break
+            }
 
             Ok(Message::CheckErrorMessages) => continue,
             Ok(msg) => {
@@ -801,9 +813,15 @@ pub fn run_passes(sess: &Session,
         }
     }
 
-    coordinator_thread.join().unwrap();
+    match coordinator_thread.join() {
+        Ok(()) => {},
+        Err(err) => {
+            panic!("error: {:?}", err);
+        }
+    }
 
     // Just in case, check this on the way out.
+    shared_emitter_main.check(sess);
     sess.diagnostic().abort_if_errors();
 
     // If in incr. comp. mode, preserve the `.o` files for potential re-use
@@ -1080,7 +1098,6 @@ pub enum Message {
     Done { success: bool },
     WorkItem(WorkItem),
     CheckErrorMessages,
-    AllWorkDone,
 }
 
 
@@ -1091,15 +1108,14 @@ pub struct Diagnostic {
 }
 
 fn start_executing_work(sess: &Session,
-                        mut work_items: Vec<WorkItem>,
+                        total_work_item_count: usize,
                         shared_emitter: SharedEmitter,
                         trans_worker_send: Sender<Message>,
+                        coordinator_send: Sender<Message>,
+                        coordinator_receive: Receiver<Message>,
                         jobserver: Client,
                         exported_symbols: Arc<ExportedSymbols>)
-                -> thread::JoinHandle<()> {
-    let (tx, rx) = channel();
-    let tx2 = tx.clone();
-
+                        -> thread::JoinHandle<()> {
     // First up, convert our jobserver into a helper thread so we can use normal
     // mpsc channels to manage our messages and such. Once we've got the helper
     // thread then request `n-1` tokens because all of our work items are ready
@@ -1110,10 +1126,11 @@ fn start_executing_work(sess: &Session,
     //
     // After we've requested all these tokens then we'll, when we can, get
     // tokens on `rx` above which will get managed in the main loop below.
+    let coordinator_send2 = coordinator_send.clone();
     let helper = jobserver.into_helper_thread(move |token| {
-        drop(tx2.send(Message::Token(token)));
+        drop(coordinator_send2.send(Message::Token(token)));
     }).expect("failed to spawn helper thread");
-    for _ in 0..work_items.len() - 1 {
+    for _ in 0..total_work_item_count - 1 {
         helper.request_token();
     }
 
@@ -1137,7 +1154,7 @@ fn start_executing_work(sess: &Session,
         remark: sess.opts.cg.remark.clone(),
         worker: 0,
         incr_comp_session_dir: sess.incr_comp_session_dir_opt().map(|r| r.clone()),
-        coordinator_send: tx.clone(),
+        coordinator_send: coordinator_send,
         diag_emitter: shared_emitter.clone(),
     };
 
@@ -1198,29 +1215,35 @@ fn start_executing_work(sess: &Session,
     // the jobserver.
 
     thread::spawn(move || {
+        let mut work_items_left = total_work_item_count;
+        let mut work_items = Vec::with_capacity(total_work_item_count);
         let mut tokens = Vec::new();
         let mut running = 0;
-        while work_items.len() > 0 || running > 0 {
+        while work_items_left > 0 || running > 0 {
 
             // Spin up what work we can, only doing this while we've got available
             // parallelism slots and work left to spawn.
-            while work_items.len() > 0 && running < tokens.len() + 1 {
-                let item = work_items.pop().unwrap();
-                let worker_index = work_items.len();
+            while work_items_left > 0 && running < tokens.len() + 1 {
+                if let Some(item) = work_items.pop() {
+                    work_items_left -= 1;
+                    let worker_index = work_items_left;
 
-                let cgcx = CodegenContext {
-                    worker: worker_index,
-                    .. cgcx.clone()
-                };
+                    let cgcx = CodegenContext {
+                        worker: worker_index,
+                        .. cgcx.clone()
+                    };
 
-                spawn_work(cgcx, item);
-                running += 1;
+                    spawn_work(cgcx, item);
+                    running += 1;
+                } else {
+                    break
+                }
             }
 
             // Relinquish accidentally acquired extra tokens
             tokens.truncate(running.saturating_sub(1));
 
-            match rx.recv().unwrap() {
+            match coordinator_receive.recv().unwrap() {
                 // Save the token locally and the next turn of the loop will use
                 // this to spawn a new unit of work, or it may get dropped
                 // immediately if we have no more work to spawn.
@@ -1228,6 +1251,10 @@ fn start_executing_work(sess: &Session,
                     tokens.push(token.expect("failed to acquire jobserver token"));
                 }
 
+                Message::WorkItem(work_item) => {
+                    work_items.push(work_item);
+                }
+
                 // If a thread exits successfully then we drop a token associated
                 // with that worker and update our `running` count. We may later
                 // re-acquire a token to continue running more work. We may also not
@@ -1245,8 +1272,6 @@ fn start_executing_work(sess: &Session,
                     shared_emitter.fatal("aborting due to worker thread panic".to_string());
                     trans_worker_send.send(Message::CheckErrorMessages).unwrap();
                 }
-                msg @ Message::WorkItem(_) |
-                msg @ Message::AllWorkDone |
                 msg @ Message::CheckErrorMessages => {
                     bug!("unexpected message: {:?}", msg);
                 }