snapshots: Handle as separate components

pkg/rlock/rlock.go

@@ -0,0 +1,44 @@
+package rlock
+
+import (
+	"sync"
+	"time"
+)
+
+type RLock struct {
+	m sync.Mutex // m is held internally
+
+	held    bool
+	holder  int
+	counter uint64
+}
+
+func (rm *RLock) Lock(id int) {
+	for {
+		rm.m.Lock()
+		if !rm.held {
+			rm.held = true
+			rm.holder = id
+			break
+		} else if rm.held && rm.holder == id {
+			break
+		} else {
+			rm.m.Unlock()
+			time.Sleep(time.Millisecond)
+			continue
+		}
+	}
+
+	rm.counter++
+	rm.m.Unlock()
+}
+
+func (rm *RLock) Unlock() {
+	rm.m.Lock()
+	rm.counter--
+	if rm.counter == 0 {
+		rm.held = false
+		rm.holder = 0
+	}
+	rm.m.Unlock()
+}