loader and singleton

pluginutils/singleton/future.go

@@ -0,0 +1,54 @@
+package singleton
+
+import (
+	"github.com/hashicorp/nomad/helper/uuid"
+	"github.com/hashicorp/nomad/pluginutils/loader"
+)
+
+// future is a sharable future for retrieving a plugin instance or any error
+// that may have occurred during the creation.
+type future struct {
+	waitCh chan struct{}
+	id     string
+
+	err      error
+	instance loader.PluginInstance
+}
+
+// newFuture returns a new pull future
+func newFuture() *future {
+	return &future{
+		waitCh: make(chan struct{}),
+		id:     uuid.Generate(),
+	}
+}
+
+func (f *future) equal(o *future) bool {
+	if f == nil && o == nil {
+		return true
+	} else if f != nil && o != nil {
+		return f.id == o.id
+	} else {
+		return false
+	}
+}
+
+// wait waits till the future has a result
+func (f *future) wait() *future {
+	<-f.waitCh
+	return f
+}
+
+// result returns the results of the future and should only ever be called after
+// wait returns.
+func (f *future) result() (loader.PluginInstance, error) {
+	return f.instance, f.err
+}
+
+// set is used to set the results and unblock any waiter. This may only be
+// called once.
+func (f *future) set(instance loader.PluginInstance, err error) {
+	f.instance = instance
+	f.err = err
+	close(f.waitCh)
+}