Source code for SCons.Job

"""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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import SCons.compat

import os
import signal

import SCons.Errors

# The default stack size (in kilobytes) of the threads used to execute
# jobs in parallel.
#
# We use a stack size of 256 kilobytes. The default on some platforms
# is too large and prevents us from creating enough threads to fully
# parallelized the build. For example, the default stack size on linux
# is 8 MBytes.

explicit_stack_size = None
default_stack_size = 256

interrupt_msg = 'Build interrupted.'


[docs]class InterruptState: def __init__(self): self.interrupted = False
[docs] def set(self): self.interrupted = True
def __call__(self): return self.interrupted
[docs]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: stack_size = explicit_stack_size if stack_size is None: stack_size = default_stack_size try: self.job = Parallel(taskmaster, num, stack_size) self.num_jobs = num except NameError: pass if self.job is None: self.job = Serial(taskmaster) self.num_jobs = 1
[docs] def run(self, postfunc=lambda: None): """Run the jobs. postfunc() will be invoked after the jobs has run. It will be invoked even if the jobs are interrupted by a keyboard interrupt (well, in fact by a signal such as either SIGINT, SIGTERM or SIGHUP). The execution of postfunc() is protected against keyboard interrupts and is guaranteed to run to completion.""" self._setup_sig_handler() try: self.job.start() finally: postfunc() self._reset_sig_handler()
[docs] def were_interrupted(self): """Returns whether the jobs were interrupted by a signal.""" return self.job.interrupted()
[docs] def _setup_sig_handler(self): """Setup an interrupt handler so that SCons can shutdown cleanly in various conditions: a) SIGINT: Keyboard interrupt b) SIGTERM: kill or system shutdown c) SIGHUP: Controlling shell exiting We handle all of these cases by stopping the taskmaster. It turns out that it's very difficult to stop the build process by throwing asynchronously an exception such as KeyboardInterrupt. For example, the python Condition variables (threading.Condition) and queues do not seem to be asynchronous-exception-safe. It would require adding a whole bunch of try/finally block and except KeyboardInterrupt all over the place. Note also that we have to be careful to handle the case when SCons forks before executing another process. In that case, we want the child to exit immediately. """ def handler(signum, stack, self=self, parentpid=os.getpid()): if os.getpid() == parentpid: self.job.taskmaster.stop() self.job.interrupted.set() else: os._exit(2) self.old_sigint = signal.signal(signal.SIGINT, handler) self.old_sigterm = signal.signal(signal.SIGTERM, handler) try: self.old_sighup = signal.signal(signal.SIGHUP, handler) except AttributeError: pass
[docs] def _reset_sig_handler(self): """Restore the signal handlers to their previous state (before the call to _setup_sig_handler().""" signal.signal(signal.SIGINT, self.old_sigint) signal.signal(signal.SIGTERM, self.old_sigterm) try: signal.signal(signal.SIGHUP, self.old_sighup) except AttributeError: pass
[docs]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 self.interrupted = InterruptState()
[docs] 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 True: task = self.taskmaster.next_task() if task is None: break try: task.prepare() if task.needs_execute(): task.execute() except Exception: if self.interrupted(): try: raise SCons.Errors.BuildError( task.targets[0], errstr=interrupt_msg) except: task.exception_set() else: 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() self.taskmaster.cleanup()
# 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:
[docs] 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, interrupted): threading.Thread.__init__(self) self.setDaemon(1) self.requestQueue = requestQueue self.resultsQueue = resultsQueue self.interrupted = interrupted self.start()
[docs] def run(self): while True: task = self.requestQueue.get() if task is None: # The "None" value is used as a sentinel by # ThreadPool.cleanup(). This indicates that there # are no more tasks, so we should quit. break try: if self.interrupted(): raise SCons.Errors.BuildError( task.targets[0], errstr=interrupt_msg) task.execute() except: task.exception_set() ok = False else: ok = True self.resultsQueue.put((task, ok))
[docs] class ThreadPool: """This class is responsible for spawning and managing worker threads.""" def __init__(self, num, stack_size, interrupted): """Create the request and reply queues, and 'num' worker threads. One must specify the stack size of the worker threads. The stack size is specified in kilobytes. """ self.requestQueue = queue.Queue(0) self.resultsQueue = queue.Queue(0) try: prev_size = threading.stack_size(stack_size*1024) except AttributeError as e: # Only print a warning if the stack size has been # explicitly set. if explicit_stack_size is not None: msg = "Setting stack size is unsupported by this version of Python:\n " + \ e.args[0] SCons.Warnings.warn(SCons.Warnings.StackSizeWarning, msg) except ValueError as e: msg = "Setting stack size failed:\n " + str(e) SCons.Warnings.warn(SCons.Warnings.StackSizeWarning, msg) # Create worker threads self.workers = [] for _ in range(num): worker = Worker(self.requestQueue, self.resultsQueue, interrupted) self.workers.append(worker) if 'prev_size' in locals(): threading.stack_size(prev_size)
[docs] def put(self, task): """Put task into request queue.""" self.requestQueue.put(task)
[docs] def get(self): """Remove and return a result tuple from the results queue.""" return self.resultsQueue.get()
[docs] def preparation_failed(self, task): self.resultsQueue.put((task, False))
[docs] def cleanup(self): """ Shuts down the thread pool, giving each worker thread a chance to shut down gracefully. """ # For each worker thread, put a sentinel "None" value # on the requestQueue (indicating that there's no work # to be done) so that each worker thread will get one and # terminate gracefully. for _ in self.workers: self.requestQueue.put(None) # Wait for all of the workers to terminate. # # If we don't do this, later Python versions (2.4, 2.5) often # seem to raise exceptions during shutdown. This happens # in requestQueue.get(), as an assertion failure that # requestQueue.not_full is notified while not acquired, # seemingly because the main thread has shut down (or is # in the process of doing so) while the workers are still # trying to pull sentinels off the requestQueue. # # Normally these terminations should happen fairly quickly, # but we'll stick a one-second timeout on here just in case # someone gets hung. for worker in self.workers: worker.join(1.0) self.workers = []
[docs] 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, stack_size): """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.interrupted = InterruptState() self.tp = ThreadPool(num, stack_size, self.interrupted) self.maxjobs = num
[docs] 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 True: # 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 try: # prepare task for execution task.prepare() except: task.exception_set() task.failed() task.postprocess() else: if task.needs_execute(): # dispatch task self.tp.put(task) jobs = jobs + 1 else: task.executed() task.postprocess() 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 True: task, ok = self.tp.get() jobs = jobs - 1 if ok: task.executed() else: if self.interrupted(): try: raise SCons.Errors.BuildError( task.targets[0], errstr=interrupt_msg) except: task.exception_set() # Let the failed() callback function arrange # for the build to stop if that's appropriate. task.failed() task.postprocess() if self.tp.resultsQueue.empty(): break self.tp.cleanup() self.taskmaster.cleanup()
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