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| author | Russ Cox <rsc@golang.org> | 2012-03-27 12:22:19 -0400 |
|---|---|---|
| committer | Russ Cox <rsc@golang.org> | 2012-03-27 12:22:19 -0400 |
| commit | 5eb007dedeb59a52a3000202dcb162a3677a384b (patch) | |
| tree | 12a2cef73e5e622222822d2a25c08c662e4fb084 | |
| parent | 9d7076b178e3b688a8421a8ce02466a3701d31a0 (diff) | |
| download | go-5eb007dedeb59a52a3000202dcb162a3677a384b.tar.gz go-5eb007dedeb59a52a3000202dcb162a3677a384b.zip | |
runtime: work around false negative in deadlock detection
Not a complete fix for issue 3342, but fixes the trivial case.
There may still be a race in the instants before and after
a scavenger-induced garbage collection.
Intended to be "obviously safe": a call to runtime·gosched
before main.main is no different than a call to runtime.Gosched
at the beginning of main.main, and it is (or had better be)
safe to call runtime.Gosched at any point during main.
Update #3342.
R=iant
CC=golang-dev
https://golang.org/cl/5919052
| -rw-r--r-- | src/pkg/runtime/proc.c | 19 | ||||
| -rw-r--r-- | test/fixedbugs/bug429.go | 13 | ||||
| -rw-r--r-- | test/golden.out | 3 |
3 files changed, 35 insertions, 0 deletions
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c index 962f748ce8..04a9926283 100644 --- a/src/pkg/runtime/proc.c +++ b/src/pkg/runtime/proc.c @@ -236,6 +236,11 @@ runtime·main(void) if(!runtime·sched.lockmain) runtime·UnlockOSThread(); + // The deadlock detection has false negatives. + // Let scvg start up, to eliminate the false negative + // for the trivial program func main() { select{} }. + runtime·gosched(); + main·main(); runtime·exit(0); for(;;) @@ -591,6 +596,20 @@ top: } // Look for deadlock situation. + // There is a race with the scavenger that causes false negatives: + // if the scavenger is just starting, then we have + // scvg != nil && grunning == 0 && gwait == 0 + // and we do not detect a deadlock. It is possible that we should + // add that case to the if statement here, but it is too close to Go 1 + // to make such a subtle change. Instead, we work around the + // false negative in trivial programs by calling runtime.gosched + // from the main goroutine just before main.main. + // See runtime·main above. + // + // On a related note, it is also possible that the scvg == nil case is + // wrong and should include gwait, but that does not happen in + // standard Go programs, which all start the scavenger. + // if((scvg == nil && runtime·sched.grunning == 0) || (scvg != nil && runtime·sched.grunning == 1 && runtime·sched.gwait == 0 && (scvg->status == Grunning || scvg->status == Gsyscall))) { diff --git a/test/fixedbugs/bug429.go b/test/fixedbugs/bug429.go new file mode 100644 index 0000000000..c1bd1d4bb9 --- /dev/null +++ b/test/fixedbugs/bug429.go @@ -0,0 +1,13 @@ +// $G $D/$F.go && $L $F.$A && ! ./$A.out || echo BUG: bug429 + +// Copyright 2012 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Should print deadlock message, not hang. + +package main + +func main() { + select {} +} diff --git a/test/golden.out b/test/golden.out index 764f561969..376af8e53c 100644 --- a/test/golden.out +++ b/test/golden.out @@ -15,6 +15,9 @@ == fixedbugs/ +=========== fixedbugs/bug429.go +throw: all goroutines are asleep - deadlock! + == bugs/ =========== bugs/bug395.go |