Merge: Introduces JoinTask, joinabale tasks

JoinTask prototype

Pull-Request: #1853
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

lib/pthreads/concurrent_collections.nit

@@ -499,4 +499,12 @@ class ConcurrentList[E]
 		real_collection.push(e)
 		mutex.unlock
 	end
+
+	redef fun shift
+	do
+		mutex.lock
+		var value = real_collection.shift
+		mutex.unlock
+		return value
+	end
 end

lib/pthreads/examples/jointask_example.nit

@@ -0,0 +1,52 @@
+# This file is part of NIT (http://www.nitlanguage.org).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#	 http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Simple example of joinable task using threadpool
+module jointask_example
+
+import threadpool
+
+# Task computing a string
+class StringTask
+	super JoinTask
+
+	# Sleeping time
+	var sec: Int
+
+	# result of `self` execution
+	var value: String
+
+	# ID for printing
+	var id: Int
+
+	redef fun main do
+		nanosleep(sec, 0)
+		value += " id: {id}"
+	end
+end
+
+var tp = new ThreadPool
+var t0 = new StringTask(10, "First, long task", 0)
+var tasks = new Array[StringTask]
+for i in 5.times do
+	tasks.add(new StringTask(1, "Small task", i + 1))
+end
+tp.execute(t0)
+for t in tasks do tp.execute(t)
+for t in tasks do
+	t.join
+	print t.value
+end
+t0.join
+print t0.value

lib/pthreads/examples/threadpool_example.nit

@@ -19,7 +19,7 @@ import threadpool
 
 # Task printing "hello world" on standard output
 class HWTask
-	super Task
+	super JoinTask
 
 	# Sleeping time
 	var sec: Int

lib/pthreads/threadpool.nit

@@ -20,7 +20,7 @@ import concurrent_collections
 
 # A simple ThreadPool implemented with an array
 class ThreadPool
-	private var queue = new ConcurrentList[Task].wrap(new List[Task])
+	private var queue = new ConcurrentList[JoinTask].wrap(new List[JoinTask])
 	private var mutex = new Mutex
 	private var cond = new NativePthreadCond
 
@@ -37,7 +37,7 @@ class ThreadPool
 	private fun set_nb_threads(nb: nullable Int) is autoinit do nb_threads = nb or else 5
 
 	# Adds a Task into the queue
-	fun execute(task: Task) do
+	fun execute(task: JoinTask) do
 		queue.push(task)
 		cond.signal
 	end
@@ -47,20 +47,49 @@ end
 private class PoolThread
 	super Thread
 
-	var queue: ConcurrentList[Task]
+	var queue: ConcurrentList[JoinTask]
 	var mutex: Mutex
 	var cond : NativePthreadCond
 
 	redef fun main do
 		loop
-			var t: nullable Task = null
+			var t: nullable JoinTask = null
 			mutex.lock
 			if queue.is_empty then cond.wait(mutex.native.as(not null))
 			if not queue.is_empty then
-				t = queue.pop
+				t = queue.shift
 			end
 			mutex.unlock
-			if t != null then t.main
+			if t != null then
+				t.main
+				t.mutex.lock
+				t.is_done = true
+				var tcond = t.cond
+				if tcond != null then tcond.signal
+				t.mutex.unlock
+			end
+		end
+	end
+end
+
+# A Task which is joinable, meaning it can return a value and if the value is not set yet, it blocks the execution
+class JoinTask
+	super Task
+
+	# Is `self` done ?
+	var is_done = false
+
+	private var mutex = new Mutex
+	private var cond: nullable NativePthreadCond = null
+
+	# Return immediatly if the task terminated, or block waiting for `self` to terminate
+	fun join do
+		mutex.lock
+		if not is_done then
+			var cond = new NativePthreadCond
+			self.cond = cond
+			cond.wait(mutex.native.as(not null))
 		end
+		mutex.unlock
 	end
 end

tests/sav/jointask_example.res

@@ -0,0 +1,6 @@
+Small task id: 1
+Small task id: 2
+Small task id: 3
+Small task id: 4
+Small task id: 5
+First, long task id: 0