move Gate type to ipc package and use it in stress tool

This allows to print what programs stress executes.

1 files changed, 54 insertions, 0 deletions

diff --git a/ipc/gate.go b/ipc/gate.go
new file mode 100644
index 000000000..941dc9f2a
--- /dev/null
+++ b/ipc/gate.go
@@ -0,0 +1,54 @@
+// Copyright 2015 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package ipc
+
+import (
+	"sync"
+)
+
+// Gate limits concurrency level and window to the given value.
+// Limitation of concurrency window means that if a very old activity is still
+// running it will not let new activities to start even if concurrency level is low.
+type Gate struct {
+	cv   *sync.Cond
+	busy []bool
+	pos  int
+}
+
+func NewGate(c int) *Gate {
+	return &Gate{
+		cv:   sync.NewCond(new(sync.Mutex)),
+		busy: make([]bool, c),
+	}
+}
+
+func (g *Gate) Enter() int {
+	g.cv.L.Lock()
+	for g.busy[g.pos] {
+		g.cv.Wait()
+	}
+	idx := g.pos
+	g.pos++
+	if g.pos >= len(g.busy) {
+		g.pos = 0
+	}
+	g.busy[idx] = true
+	g.cv.L.Unlock()
+	return idx
+}
+
+func (g *Gate) Leave(idx int, f func()) {
+	g.cv.L.Lock()
+	if !g.busy[idx] {
+		panic("broken gate")
+	}
+	if f != nil {
+		f()
+	}
+	g.busy[idx] = false
+	if idx == g.pos {
+		g.cv.Broadcast()
+	}
+	g.cv.L.Unlock()
+}