Implement jobserver event communication

Author: Mark-Simulacrum

Cargo.lock

@@ -3649,6 +3649,7 @@ version = "0.0.0"
 dependencies = [
  "jobserver",
  "lazy_static 1.3.0",
+ "serialize",
 ]
 
 [[package]]

src/librustc_jobserver/Cargo.toml

@@ -12,3 +12,4 @@ doctest = false
 [dependencies]
 jobserver_crate = { version = "0.1.13", package = "jobserver" }
 lazy_static = "1"
+rustc_serialize = { path = "../libserialize", package = "serialize" }

src/librustc_jobserver/lib.rs

@@ -1,6 +1,7 @@
 use jobserver_crate::Client;
 use lazy_static::lazy_static;
 use std::sync::atomic::{Ordering, AtomicUsize};
+use rustc_serialize::json::as_json;
 
 lazy_static! {
     // We can only call `from_env` once per process
@@ -30,17 +31,6 @@ lazy_static! {
     };
 }
 
-// Unlike releasing tokens, there's not really a "one size fits all" approach, as we have two
-// primary ways of acquiring a token: via the helper thread, and via the acquire_thread function.
-//
-// That makes this function necessary unlike in the release case where everything is piped through
-// `release_thread`.
-fn notify_acquiring_token() {
-    if should_notify() {
-        // FIXME: tell Cargo of our interest
-    }
-}
-
 const EMPTY: usize = 0;
 const CARGO_REQUESTED: usize = 1;
 const MAKE_REQUESTED: usize = 2;
@@ -110,11 +100,34 @@ pub fn helper_thread<F>(mut cb: F) -> HelperThread
     }
 }
 
+#[derive(RustcEncodable)]
+enum Event {
+    WillAcquire,
+    Release,
+}
+
+#[derive(RustcEncodable)]
+struct JobserverNotification {
+    jobserver_event: Event,
+}
+
+// Unlike releasing tokens, there's not really a "one size fits all" approach, as we have two
+// primary ways of acquiring a token: via the helper thread, and via the acquire_thread function.
+fn notify_acquiring_token() {
+    if should_notify() {
+        eprintln!("{}", as_json(&JobserverNotification { jobserver_event: Event::WillAcquire }));
+    }
+}
+
 pub fn acquire_thread() {
     notify_acquiring_token();
     GLOBAL_CLIENT.acquire_raw().ok();
 }
 
 pub fn release_thread() {
-    GLOBAL_CLIENT.release_raw().ok();
+    if should_notify() {
+        eprintln!("{}", as_json(&JobserverNotification { jobserver_event: Event::Release }));
+    } else {
+        GLOBAL_CLIENT.release_raw().ok();
+    }
 }