Merge pull request #41 from konsumlamm/waitgroups

Improve `waitgroups`

tests/twaitgroups.nim

@@ -0,0 +1,42 @@
+import threading/waitgroups
+
+block basic:
+  var wg = createWaitGroup()
+  wg.enter(10)
+  for _ in 1..10:
+    wg.leave()
+  wg.wait()
+
+block multiple_threads:
+  var data: array[10, int]
+  var wg = createWaitGroup()
+
+  proc worker(i: int) =
+    data[i] = 42
+    wg.leave()
+
+  var threads: array[10, Thread[int]]
+  wg.enter(10)
+  for i in 0..<10:
+    createThread(threads[i], worker, i)
+
+  wg.wait()
+  for x in data:
+    doAssert x == 42
+
+  joinThreads(threads)
+
+block multiple_waits:
+  var wg = createWaitGroup()
+  wg.enter(1)
+
+  proc worker() =
+    wg.wait()
+
+  var threads: array[10, Thread[void]]
+  for i in 0..<10:
+    createThread(threads[i], worker)
+
+  wg.leave()
+
+  joinThreads(threads)

threading/waitgroups.nim

@@ -8,11 +8,32 @@
 
 ## Wait groups for Nim.
 
+runnableExamples:
+
+  var data: array[10, int]
+  var wg = createWaitGroup()
+
+  proc worker(i: int) =
+    data[i] = 42
+    wg.leave()
+
+  var threads: array[10, Thread[int]]
+  wg.enter(10)
+  for i in 0..<10:
+    createThread(threads[i], worker, i)
+
+  wg.wait()
+  for x in data:
+    assert x == 42
+
+  joinThreads(threads)
+
+
 import std / [locks]
 
 type
-  WaitGroup* = object ## \
-    ## A WaitGroup is an synchronization object that can be used to `wait` until
+  WaitGroup* = object
+    ## A `WaitGroup` is a synchronization object that can be used to `wait` until
     ## all workers have completed.
     c: Cond
     L: Lock
@@ -36,19 +57,21 @@ proc createWaitGroup*(): WaitGroup =
   initCond(result.c)
   initLock(result.L)
 
-proc enter*(b: var WaitGroup; delta = 1) {.inline.} =
-  ## Tells the WaitGroup that one or more workers (the `delta` parameter says
-  ## how many) "entered" which means to increase the counter that counts how
+proc enter*(b: var WaitGroup; delta: Natural = 1) {.inline.} =
+  ## Tells the `WaitGroup` that one or more workers (the `delta` parameter says
+  ## how many) "entered", which means to increase the counter that counts how
   ## many workers to wait for.
   acquire(b.L)
   inc b.runningTasks, delta
   release(b.L)
 
 proc leave*(b: var WaitGroup) {.inline.} =
-  ## Tells the WaitGroup that one worker has finished its task.
+  ## Tells the `WaitGroup` that one worker has finished its task.
   acquire(b.L)
-  dec b.runningTasks
-  signal(b.c)
+  if b.runningTasks > 0:
+    dec b.runningTasks
+    if b.runningTasks == 0:
+      broadcast(b.c)
   release(b.L)
 
 proc wait*(b: var WaitGroup) =