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| author | Rob Pike <r@golang.org> | 2014-09-16 14:00:01 -0700 |
|---|---|---|
| committer | Rob Pike <r@golang.org> | 2014-09-16 14:00:01 -0700 |
| commit | 000836fa382e6a9806a176c6021f9b9c56277c8c (patch) | |
| tree | 69e02ecd7274e4208b3126cac70ff87ef1286fe7 /src/sync | |
| parent | f85acc6b30ec22f56f9642ac72679fc31b72208c (diff) | |
| download | go-000836fa382e6a9806a176c6021f9b9c56277c8c.tar.gz | |
sync/once: panicking functions still marked as complete
This is a corner case, and one that was even tested, but this
CL changes the behavior to say that f is "complete" even if it panics.
But don't think of it that way, think of it as sync.Once runs
the function only the first time it is called, rather than
repeatedly until a run of the function completes.
Fixes issue 8118.
LGTM=dvyukov
R=golang-codereviews, dvyukov
CC=golang-codereviews
https://codereview.appspot.com/137350043
Diffstat (limited to 'src/sync')
| -rw-r--r-- | src/sync/once.go | 7 | ||||
| -rw-r--r-- | src/sync/once_test.go | 8 |
2 files changed, 11 insertions, 4 deletions
diff --git a/src/sync/once.go b/src/sync/once.go index 161ae3b3e..10b42fddc 100644 --- a/src/sync/once.go +++ b/src/sync/once.go @@ -15,7 +15,7 @@ type Once struct { } // Do calls the function f if and only if Do is being called for the -// first time for this instance of Once. In other words, given +// first time for this instance of Once. In other words, given // var once Once // if once.Do(f) is called multiple times, only the first call will invoke f, // even if f has a different value in each invocation. A new instance of @@ -29,6 +29,9 @@ type Once struct { // Because no call to Do returns until the one call to f returns, if f causes // Do to be called, it will deadlock. // +// If f panics, Do considers it to have returned; future calls of Do return +// without calling f. +// func (o *Once) Do(f func()) { if atomic.LoadUint32(&o.done) == 1 { return @@ -37,7 +40,7 @@ func (o *Once) Do(f func()) { o.m.Lock() defer o.m.Unlock() if o.done == 0 { + defer atomic.StoreUint32(&o.done, 1) f() - atomic.StoreUint32(&o.done, 1) } } diff --git a/src/sync/once_test.go b/src/sync/once_test.go index 8afda82f3..10beefde3 100644 --- a/src/sync/once_test.go +++ b/src/sync/once_test.go @@ -44,8 +44,12 @@ func TestOncePanic(t *testing.T) { for i := 0; i < 2; i++ { func() { defer func() { - if recover() == nil { - t.Fatalf("Once.Do() has not panic'ed") + r := recover() + if r == nil && i == 0 { + t.Fatalf("Once.Do() has not panic'ed on first iteration") + } + if r != nil && i == 1 { + t.Fatalf("Once.Do() has panic'ed on second iteration") } }() once.Do(func() { |