path: root/src/engine/SCons/Job.py

"""SCons.Job

This module defines the Serial and Parallel classes that execute tasks to
complete a build. The Jobs class provides a higher level interface to start,
stop, and wait on jobs.

"""

#
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__revision__ = "__FILE__ __REVISION__ __DATE__ __DEVELOPER__"

import SCons.compat

class Jobs:
    """An instance of this class initializes N jobs, and provides
    methods for starting, stopping, and waiting on all N jobs.
    """

    def __init__(self, num, taskmaster):
        """
        create 'num' jobs using the given taskmaster.

        If 'num' is 1 or less, then a serial job will be used,
        otherwise a parallel job with 'num' worker threads will
        be used.

        The 'num_jobs' attribute will be set to the actual number of jobs
        allocated.  If more than one job is requested but the Parallel
        class can't do it, it gets reset to 1.  Wrapping interfaces that
        care should check the value of 'num_jobs' after initialization.
        """

        self.job = None
        if num > 1:
            try:
                self.job = Parallel(taskmaster, num)
                self.num_jobs = num
            except NameError:
                pass
        if self.job is None:
            self.job = Serial(taskmaster)
            self.num_jobs = 1

    def run(self):
        """run the job"""
        try:
            self.job.start()
        except KeyboardInterrupt:
            # mask any further keyboard interrupts so that scons
            # can shutdown cleanly:
            # (this only masks the keyboard interrupt for Python,
            #  child processes can still get the keyboard interrupt)
            import signal
            signal.signal(signal.SIGINT, signal.SIG_IGN)
            raise

class Serial:
    """This class is used to execute tasks in series, and is more efficient
    than Parallel, but is only appropriate for non-parallel builds. Only
    one instance of this class should be in existence at a time.

    This class is not thread safe.
    """

    def __init__(self, taskmaster):
        """Create a new serial job given a taskmaster. 

        The taskmaster's next_task() method should return the next task
        that needs to be executed, or None if there are no more tasks. The
        taskmaster's executed() method will be called for each task when it
        is successfully executed or failed() will be called if it failed to
        execute (e.g. execute() raised an exception)."""
        
        self.taskmaster = taskmaster

    def start(self):
        """Start the job. This will begin pulling tasks from the taskmaster
        and executing them, and return when there are no more tasks. If a task
        fails to execute (i.e. execute() raises an exception), then the job will
        stop."""
        
        while 1:
            task = self.taskmaster.next_task()

            if task is None:
                break

            try:
                task.prepare()
                task.execute()
            except KeyboardInterrupt:
                raise
            except:
                task.exception_set()
                # Let the failed() callback function arrange for the
                # build to stop if that's appropriate.
                task.failed()
            else:
                task.executed()

            task.postprocess()


# Trap import failure so that everything in the Job module but the
# Parallel class (and its dependent classes) will work if the interpreter
# doesn't support threads.
try:
    import Queue
    import threading
except ImportError:
    pass
else:
    class Worker(threading.Thread):
        """A worker thread waits on a task to be posted to its request queue,
        dequeues the task, executes it, and posts a tuple including the task
        and a boolean indicating whether the task executed successfully. """

        def __init__(self, requestQueue, resultsQueue):
            threading.Thread.__init__(self)
            self.setDaemon(1)
            self.requestQueue = requestQueue
            self.resultsQueue = resultsQueue
            self.start()

        def run(self):
            while 1:
                task = self.requestQueue.get()

                try:
                    task.execute()
                except KeyboardInterrupt:
                    # be explicit here for test/interrupts.py
                    ok = False
                except:
                    task.exception_set()
                    ok = False
                else:
                    ok = True

                self.resultsQueue.put((task, ok))

    class ThreadPool:
        """This class is responsible for spawning and managing worker threads."""

        def __init__(self, num):
            """Create the request and reply queues, and 'num' worker threads."""
            self.requestQueue = Queue.Queue(0)
            self.resultsQueue = Queue.Queue(0)

            # Create worker threads
            for i in range(num):
                Worker(self.requestQueue, self.resultsQueue)

        def put(self, obj):
            """Put task into request queue."""
            self.requestQueue.put(obj)

        def get(self, block = True):
            """Remove and return a result tuple from the results queue."""
            return self.resultsQueue.get(block)

        def preparation_failed(self, obj):
            self.resultsQueue.put((obj, 0))

    class Parallel:
        """This class is used to execute tasks in parallel, and is somewhat 
        less efficient than Serial, but is appropriate for parallel builds.

        This class is thread safe.
        """

        def __init__(self, taskmaster, num):
            """Create a new parallel job given a taskmaster.

            The taskmaster's next_task() method should return the next
            task that needs to be executed, or None if there are no more
            tasks. The taskmaster's executed() method will be called
            for each task when it is successfully executed or failed()
            will be called if the task failed to execute (i.e. execute()
            raised an exception).

            Note: calls to taskmaster are serialized, but calls to
            execute() on distinct tasks are not serialized, because
            that is the whole point of parallel jobs: they can execute
            multiple tasks simultaneously. """

            self.taskmaster = taskmaster
            self.tp = ThreadPool(num)

            self.maxjobs = num

        def start(self):
            """Start the job. This will begin pulling tasks from the
            taskmaster and executing them, and return when there are no
            more tasks. If a task fails to execute (i.e. execute() raises
            an exception), then the job will stop."""

            jobs = 0
            
            while 1:
                # Start up as many available tasks as we're
                # allowed to.
                while jobs < self.maxjobs:
                    task = self.taskmaster.next_task()
                    if task is None:
                        break

                    # prepare task for execution
                    try:
                        task.prepare()
                    except KeyboardInterrupt:
                        raise
                    except:
                        # Let the failed() callback function arrange
                        # for the build to stop if that's appropriate.
                        task.exception_set()
                        self.tp.preparation_failed(task)
                        jobs = jobs + 1
                        continue

                    # dispatch task
                    self.tp.put(task)
                    jobs = jobs + 1

                if not task and not jobs: break

                # Let any/all completed tasks finish up before we go
                # back and put the next batch of tasks on the queue.
                while 1:
                    task, ok = self.tp.get()

                    jobs = jobs - 1
                    if ok:
                        task.executed()
                    else:
                        task.failed()

                    task.postprocess()

                    if self.tp.resultsQueue.empty():
                        break