sync/waitgroup: use value mutex and semaphore; remove sync.Waiter (#8431)

vlib/sync/waiter_nix.c.v

@@ -1,22 +0,0 @@
-// 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
-
-[ref_only]
-struct Waiter{
-mut:
-	mx &Mutex
-}
-
-pub fn (mut w Waiter) wait() {
-	w.mx.m_lock()
-}
-
-pub fn (mut w Waiter) stop() {
-	w.mx.unlock()
-}
-pub fn new_waiter() &Waiter {
-	w := &Waiter{mx: new_mutex()}
-	return w
-}

vlib/sync/waiter_windows.c.v

@@ -1,35 +0,0 @@
-// 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
-
-// We cannot simply use Mutex.lock() in the waitgroup.wait() method
-// as it will not block since it's used in the same thread.
-// docs:
-// Any thread with a handle to a mutex object can use one of the
-// wait functions to request ownership of the mutex object.
-// If the mutex object is owned by another thread, the wait
-// function blocks the requesting thread until the owning thread
-// releases the mutex object using the ReleaseMutex function.
-// Source:
-// https://docs.microsoft.com/en-us/windows/win32/sync/mutex-objects
-
-[ref_only]
-struct Waiter{
-mut:
-	event MHANDLE
-}
-
-pub fn (mut w Waiter) wait() {
-	C.WaitForSingleObject(w.event, C.INFINITE) // infinite wait
-}
-
-pub fn (mut w Waiter) stop() {
-	C.SetEvent(w.event)
-}
-pub fn new_waiter() &Waiter {
-	unsafe {
-		sm := &Waiter{event: MHANDLE(C.CreateEvent(0, false, true, 0))}
-		return sm
-	}
-}

vlib/sync/waitgroup.v

@@ -14,15 +14,15 @@ module sync
 struct WaitGroup {
 mut:
 	task_count       int // current task count
-	task_count_mutex &Mutex // This mutex protects the task_count count in add()
-	wait_blocker     &Waiter = &Waiter(0) // This blocks the wait() until released by add()
+	task_count_mutex Mutex // This mutex protects the task_count count in add()
+	wait_blocker     Semaphore // This blocks the wait() until released by add()
 }
 
 pub fn new_waitgroup() &WaitGroup {
-	return &WaitGroup{
-		task_count_mutex: new_mutex()
-		wait_blocker: new_waiter()
-	}
+	mut wg := &WaitGroup{}
+	wg.task_count_mutex.init()
+	wg.wait_blocker.init(1)
+	return wg
 }
 
 // add increments (+ve delta) or decrements (-ve delta) task count by delta
@@ -43,7 +43,7 @@ pub fn (mut wg WaitGroup) add(delta int) {
 		panic('Negative number of jobs in waitgroup')
 	}
 	if wg.task_count == 0 { // if no more task_count tasks
-		wg.wait_blocker.stop() // unblock wait()
+		wg.wait_blocker.post() // unblock wait()
 	}
 }
 
@@ -55,5 +55,5 @@ pub fn (mut wg WaitGroup) done() {
 // wait blocks until all tasks are done (task count becomes zero)
 pub fn (mut wg WaitGroup) wait() {
 	wg.wait_blocker.wait() // blocks until task_count becomes 0
-	wg.wait_blocker.stop() // allow other wait()s to unblock or reuse wait group
+	wg.wait_blocker.post() // allow other wait()s to unblock or reuse wait group
 }