syncs: add LockFunc, LockValue, LockValues, and Mutexdsnet/syncs-lock

The first 3 functions are helpers for running functions
under the protection of a lock.

The Mutex type is a wrapper over sync.Mutex with a Do method
that runs a function under the protection of a lock.

Updates #11038
Updates #cleanup

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

1 files changed, 37 insertions, 0 deletions

diff --git a/syncs/lock_example_test.go b/syncs/lock_example_test.go
new file mode 100644
index 000000000..13184c7c0
--- /dev/null
+++ b/syncs/lock_example_test.go
@@ -0,0 +1,37 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package syncs_test
+
+import (
+	"encoding/hex"
+	"log"
+	"sync"
+
+	"tailscale.com/syncs"
+)
+
+func ExampleLockFunc() {
+	var nodesMu sync.Mutex
+	var nodes []string
+	syncs.LockFunc(&nodesMu, func() { nodes = append(nodes, "node123") })
+}
+
+func ExampleLockValue() {
+	var nodesMu sync.Mutex
+	var nodes []string
+	n := syncs.LockValue(&nodesMu, func() int { return len(nodes) })
+	log.Printf("there are %d nodes", n)
+}
+
+func ExampleLockValues() {
+	var bufferMu sync.Mutex
+	var buffer string
+	b, err := syncs.LockValues(&bufferMu, func() ([]byte, error) {
+		return hex.DecodeString(buffer)
+	})
+	if err != nil {
+		log.Fatalf("Decode error: %v", err)
+	}
+	log.Printf("decoded %d bytes", len(b))
+}