(#691): Flush the Backend buffer

kkysen · web-flow · commit 7e79f918a081 · 2022-09-27T23:06:36.000-04:00
Fixes #689. Normally the `BufWriter` in `LogBackend` is `flush`ed in `drop`, but since all of this runs from a static or a background thread, no destructors are run (reliably at least; not sure about the background thread case). Thus, we need to explicitly `flush` the buffer. I believe this may be the remaining cause of #613. This fix adds a `flush` method to `trait WriteEvent`, which is called after all `Event`s have been written so that we never lose any of the `Event`s. It's implemented by delegating to `Write::flush`, both for `BufWriter` in `LogBackend` and `stderr()` in `DebugBackend` (though that one is usually unbuffered). I discovered this while implementing #687, as the missing `flush` is reliably detected when running the `Backend` on the main thread.
diff --git a/analysis/runtime/src/runtime/backend.rs b/analysis/runtime/src/runtime/backend.rs
@@ -1,7 +1,7 @@
 use enum_dispatch::enum_dispatch;
 use fs_err::{File, OpenOptions};
 use std::fmt::Debug;
-use std::io::BufWriter;
+use std::io::{stderr, BufWriter, Write};
 use std::sync::mpsc::Receiver;
 
 use bincode;
@@ -14,6 +14,8 @@ use crate::parse::{self, AsStr, GetChoices};
 #[enum_dispatch]
 pub(super) trait WriteEvent {
     fn write(&mut self, event: Event);
+
+    fn flush(&mut self);
 }
 
 pub(super) trait DetectBackend: Sized {
@@ -56,6 +58,10 @@ impl WriteEvent for DebugBackend {
         let mir_loc = self.metadata.get(event.mir_loc);
         eprintln!("{:?}: {:?}", mir_loc, event.kind);
     }
+
+    fn flush(&mut self) {
+        stderr().flush().unwrap();
+    }
 }
 
 pub struct LogBackend {
@@ -66,6 +72,10 @@ impl WriteEvent for LogBackend {
     fn write(&mut self, event: Event) {
         bincode::serialize_into(&mut self.writer, &event).unwrap();
     }
+
+    fn flush(&mut self) {
+        self.writer.flush().unwrap();
+    }
 }
 
 #[enum_dispatch(WriteEvent)]
@@ -80,9 +90,10 @@ impl Backend {
             let done = matches!(event.kind, EventKind::Done);
             self.write(event);
             if done {
-                return;
+                break;
             }
         }
+        self.flush();
     }
 
     pub fn run(&mut self, rx: Receiver<Event>) {

Original file line number	Diff line number	Diff line change
`@@ -1,7 +1,7 @@`
`1`	`1`	`use enum_dispatch::enum_dispatch;`
`2`	`2`	`use fs_err::{File, OpenOptions};`
`3`	`3`	`use std::fmt::Debug;`
`4`		`-use std::io::BufWriter;`
	`4`	`+use std::io::{stderr, BufWriter, Write};`
`5`	`5`	`use std::sync::mpsc::Receiver;`
`6`	`6`
`7`	`7`	`use bincode;`
`@@ -14,6 +14,8 @@ use crate::parse::{self, AsStr, GetChoices};`
`14`	`14`	`#[enum_dispatch]`
`15`	`15`	`pub(super) trait WriteEvent {`
`16`	`16`	`fn write(&mut self, event: Event);`
	`17`	`+`
	`18`	`+ fn flush(&mut self);`
`17`	`19`	`}`
`18`	`20`
`19`	`21`	`pub(super) trait DetectBackend: Sized {`
`@@ -56,6 +58,10 @@ impl WriteEvent for DebugBackend {`
`56`	`58`	`let mir_loc = self.metadata.get(event.mir_loc);`
`57`	`59`	`eprintln!("{:?}: {:?}", mir_loc, event.kind);`
`58`	`60`	`}`
	`61`	`+`
	`62`	`+ fn flush(&mut self) {`
	`63`	`+ stderr().flush().unwrap();`
	`64`	`+ }`
`59`	`65`	`}`
`60`	`66`
`61`	`67`	`pub struct LogBackend {`
`@@ -66,6 +72,10 @@ impl WriteEvent for LogBackend {`
`66`	`72`	`fn write(&mut self, event: Event) {`
`67`	`73`	`bincode::serialize_into(&mut self.writer, &event).unwrap();`
`68`	`74`	`}`
	`75`	`+`
	`76`	`+ fn flush(&mut self) {`
	`77`	`+ self.writer.flush().unwrap();`
	`78`	`+ }`
`69`	`79`	`}`
`70`	`80`
`71`	`81`	`#[enum_dispatch(WriteEvent)]`
`@@ -80,9 +90,10 @@ impl Backend {`
`80`	`90`	`let done = matches!(event.kind, EventKind::Done);`
`81`	`91`	`self.write(event);`
`82`	`92`	`if done {`
`83`		`- return;`
	`93`	`+ break;`
`84`	`94`	`}`
`85`	`95`	`}`
	`96`	`+ self.flush();`
`86`	`97`	`}`
`87`	`98`
`88`	`99`	`pub fn run(&mut self, rx: Receiver<Event>) {`