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Diffstat (limited to 'libgo/go/sync/once.go')
| -rw-r--r-- | libgo/go/sync/once.go | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/libgo/go/sync/once.go b/libgo/go/sync/once.go index d8ef952..8476197 100644 --- a/libgo/go/sync/once.go +++ b/libgo/go/sync/once.go @@ -10,8 +10,13 @@ import ( // Once is an object that will perform exactly one action. type Once struct { - m Mutex + // done indicates whether the action has been performed. + // It is first in the struct because it is used in the hot path. + // The hot path is inlined at every call site. + // Placing done first allows more compact instructions on some architectures (amd64/x86), + // and fewer instructions (to calculate offset) on other architectures. done uint32 + m Mutex } // Do calls the function f if and only if Do is being called for the @@ -33,10 +38,13 @@ type Once struct { // without calling f. // func (o *Once) Do(f func()) { - if atomic.LoadUint32(&o.done) == 1 { - return + if atomic.LoadUint32(&o.done) == 0 { + // Outlined slow-path to allow inlining of the fast-path. + o.doSlow(f) } - // Slow-path. +} + +func (o *Once) doSlow(f func()) { o.m.Lock() defer o.m.Unlock() if o.done == 0 { |