src: Add DMA localagent

[barometer.git] / src / dma / vendor / github.com / go-redis / redis / internal / once.go

diff --git a/src/dma/vendor/github.com/go-redis/redis/internal/once.go b/src/dma/vendor/github.com/go-redis/redis/internal/once.go
new file mode 100644 (file)
index 0000000..64f4627
--- /dev/null
+++ b/src/dma/vendor/github.com/go-redis/redis/internal/once.go
@@ -0,0 +1,60 @@
+/*
+Copyright 2014 The Camlistore Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package internal
+
+import (
+       "sync"
+       "sync/atomic"
+)
+
+// A Once will perform a successful action exactly once.
+//
+// Unlike a sync.Once, this Once's func returns an error
+// and is re-armed on failure.
+type Once struct {
+       m    sync.Mutex
+       done uint32
+}
+
+// Do calls the function f if and only if Do has not been invoked
+// without error 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 unless
+// f returns an error.  A new instance of Once is required for each
+// function to execute.
+//
+// Do is intended for initialization that must be run exactly once.  Since f
+// is niladic, it may be necessary to use a function literal to capture the
+// arguments to a function to be invoked by Do:
+//     err := config.once.Do(func() error { return config.init(filename) })
+func (o *Once) Do(f func() error) error {
+       if atomic.LoadUint32(&o.done) == 1 {
+               return nil
+       }
+       // Slow-path.
+       o.m.Lock()
+       defer o.m.Unlock()
+       var err error
+       if o.done == 0 {
+               err = f()
+               if err == nil {
+                       atomic.StoreUint32(&o.done, 1)
+               }
+       }
+       return err
+}