sync: WaitGroup

vlib/sync/waitgroup.v

@@ -0,0 +1,37 @@
+// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module sync
+
+struct WaitGroup {
+mut:
+    mu Mutex
+    finished Mutex
+    active int
+}
+
+pub fn (wg mut WaitGroup) add(delta int) {
+    wg.mu.lock()
+    if wg.active == 0 {
+        wg.finished.lock()
+    }
+    wg.active += delta
+    if wg.active < 0 {
+        panic('Negative number of jobs in waitgroup')
+    }
+    if wg.active == 0 {
+        wg.finished.unlock()
+    }
+    wg.mu.unlock()
+}
+
+pub fn (wg mut WaitGroup) done() {
+    wg.add(-1)
+}
+
+pub fn (wg mut WaitGroup) wait() {
+    wg.finished.lock()
+    wg.finished.unlock()
+}
+