pkg/osutil: move Semaphore from pkg/instance

Semaphore is a very low-level primitive type,
while pkg/instance is a very high-level package with lots of deps.
Semaphore does not belong there, and may lead to cyclic deps
if we use it more. Move it to pkg/osutil. It's not really OS-specific,
but we don't have a better package.

1 files changed, 42 insertions, 0 deletions

diff --git a/pkg/osutil/semaphore.go b/pkg/osutil/semaphore.go
new file mode 100644
index 000000000..83d251ce0
--- /dev/null
+++ b/pkg/osutil/semaphore.go
@@ -0,0 +1,42 @@
+// Copyright 2025 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 osutil
+
+import (
+	"fmt"
+)
+
+type Semaphore struct {
+	ch chan struct{}
+}
+
+func NewSemaphore(count int) *Semaphore {
+	s := &Semaphore{
+		ch: make(chan struct{}, count),
+	}
+	for i := 0; i < count; i++ {
+		s.Signal()
+	}
+	return s
+}
+
+func (s *Semaphore) Wait() {
+	<-s.ch
+}
+
+func (s *Semaphore) WaitC() <-chan struct{} {
+	return s.ch
+}
+
+func (s *Semaphore) Available() int {
+	return len(s.ch)
+}
+
+func (s *Semaphore) Signal() {
+	if av := s.Available(); av == cap(s.ch) {
+		// Not super reliable, but let it be here just in case.
+		panic(fmt.Sprintf("semaphore capacity (%v) is exceeded (%v)", cap(s.ch), av))
+	}
+	s.ch <- struct{}{}
+}