1 files changed, 97 insertions, 0 deletions
diff --git a/lds/execqueue.go b/lds/execqueue.go
new file mode 100644
index 000000000..31ed5d754
--- /dev/null
+++ b/lds/execqueue.go
@@ -0,0 +1,97 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package lds
+
+import "sync"
+
+// execQueue implements a queue that executes function calls in a single thread,
+// in the same order as they have been queued.
+type execQueue struct {
+	mu        sync.Mutex
+	cond      *sync.Cond
+	funcs     []func()
+	closeWait chan struct{}
+}
+
+// newExecQueue creates a new execution queue.
+func newExecQueue(capacity int) *execQueue {
+	q := &execQueue{funcs: make([]func(), 0, capacity)}
+	q.cond = sync.NewCond(&q.mu)
+	go q.loop()
+	return q
+}
+
+func (q *execQueue) loop() {
+	for f := q.waitNext(false); f != nil; f = q.waitNext(true) {
+		f()
+	}
+	close(q.closeWait)
+}
+
+func (q *execQueue) waitNext(drop bool) (f func()) {
+	q.mu.Lock()
+	if drop {
+		// Remove the function that just executed. We do this here instead of when
+		// dequeuing so len(q.funcs) includes the function that is running.
+		q.funcs = append(q.funcs[:0], q.funcs[1:]...)
+	}
+	for !q.isClosed() {
+		if len(q.funcs) > 0 {
+			f = q.funcs[0]
+			break
+		}
+		q.cond.Wait()
+	}
+	q.mu.Unlock()
+	return f
+}
+
+func (q *execQueue) isClosed() bool {
+	return q.closeWait != nil
+}
+
+// canQueue returns true if more function calls can be added to the execution queue.
+func (q *execQueue) canQueue() bool {
+	q.mu.Lock()
+	ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
+	q.mu.Unlock()
+	return ok
+}
+
+// queue adds a function call to the execution queue. Returns true if successful.
+func (q *execQueue) queue(f func()) bool {
+	q.mu.Lock()
+	ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
+	if ok {
+		q.funcs = append(q.funcs, f)
+		q.cond.Signal()
+	}
+	q.mu.Unlock()
+	return ok
+}
+
+// quit stops the exec queue.
+// quit waits for the current execution to finish before returning.
+func (q *execQueue) quit() {
+	q.mu.Lock()
+	if !q.isClosed() {
+		q.closeWait = make(chan struct{})
+		q.cond.Signal()
+	}
+	q.mu.Unlock()
+	<-q.closeWait
+}