This document describes the current stable version of Celery (5.6). For development docs, go here.

# Source code for celery.utils.debug

    """Utilities for debugging memory usage, blocking calls, etc."""
    import os
    import sys
    import traceback
    from contextlib import contextmanager
    from functools import partial
    from pprint import pprint

    from celery.platforms import signals
    from celery.utils.text import WhateverIO

    try:
        from psutil import Process
    except ImportError:
        Process = None

    __all__ = (
        'blockdetection', 'sample_mem', 'memdump', 'sample',
        'humanbytes', 'mem_rss', 'ps', 'cry',
    )

    UNITS = (
        (2 ** 40.0, 'TB'),
        (2 ** 30.0, 'GB'),
        (2 ** 20.0, 'MB'),
        (2 ** 10.0, 'KB'),
        (0.0, 'b'),
    )

    _process = None
    _mem_sample = []

    def _on_blocking(signum, frame):
        import inspect
        raise RuntimeError(
            f'Blocking detection timed-out at: {inspect.getframeinfo(frame)}'
        )

    @contextmanager
    def blockdetection(timeout):
        """Context that raises an exception if process is blocking.

        Uses ``SIGALRM`` to detect blocking functions.
        """
        if not timeout:
            yield
        else:
            old_handler = signals['ALRM']
            old_handler = None if old_handler == _on_blocking else old_handler

            signals['ALRM'] = _on_blocking

            try:
                yield signals.arm_alarm(timeout)
            finally:
                if old_handler:
                    signals['ALRM'] = old_handler
                signals.reset_alarm()

    def sample_mem():
        """Sample RSS memory usage.

        Statistics can then be output by calling :func:`memdump`.
        """
        current_rss = mem_rss()
        _mem_sample.append(current_rss)
        return current_rss

    def _memdump(samples=10):  # pragma: no cover
        S = _mem_sample
        prev = list(S) if len(S) <= samples else sample(S, samples)
        _mem_sample[:] = []
        import gc
        gc.collect()
        after_collect = mem_rss()
        return prev, after_collect

    def memdump(samples=10, file=None):  # pragma: no cover
        """Dump memory statistics.

        Will print a sample of all RSS memory samples added by
        calling :func:`sample_mem`, and in addition print
        used RSS memory after :func:`gc.collect`.
        """
        say = partial(print, file=file)
        if ps() is None:
            say('- rss: (psutil not installed).')
            return
        prev, after_collect = _memdump(samples)
        if prev:
            say('- rss (sample):')
            for mem in prev:
                say(f'-    > {mem},')
        say(f'- rss (end): {after_collect}.')

    def sample(x, n, k=0):
        """Given a list `x` a sample of length ``n`` of that list is returned.

        For example, if `n` is 10, and `x` has 100 items, a list of every tenth.
        item is returned.

        ``k`` can be used as offset.
        """
        j = len(x) // n
        for _ in range(n):
            try:
                yield x[k]
            except IndexError:
                break
            k += j

    def hfloat(f, p=5):
        """Convert float to value suitable for humans.

        Arguments:
            f (float): The floating point number.
            p (int): Floating point precision (default is 5).
        """
        i = int(f)
        return i if i == f else '{0:.{p}}'.format(f, p=p)

    def humanbytes(s):
        """Convert bytes to human-readable form (e.g., KB, MB)."""
        return next(
            f'{hfloat(s / div if div else s)}{unit}'
            for div, unit in UNITS if s >= div
        )

    def mem_rss():
        """Return RSS memory usage as a humanized string."""
        p = ps()
        if p is not None:
            return humanbytes(_process_memory_info(p).rss)

    def ps():  # pragma: no cover
        """Return the global :class:`psutil.Process` instance.

        Note:
            Returns :const:`None` if :pypi:`psutil` is not installed.
        """
        global _process
        if _process is None and Process is not None:
            _process = Process(os.getpid())
        return _process

    def _process_memory_info(process):
        try:
            return process.memory_info()
        except AttributeError:
            return process.get_memory_info()

    def cry(out=None, sepchr='=', seplen=49):  # pragma: no cover
        """Return stack-trace of all active threads.

        See Also:
            Taken from https://gist.github.com/737056.
        """
        import threading

        out = WhateverIO() if out is None else out
        P = partial(print, file=out)

        # get a map of threads by their ID so we can print their names
        # during the traceback dump
        tmap = {t.ident: t for t in threading.enumerate()}

        sep = sepchr * seplen
        for tid, frame in sys._current_frames().items():
            thread = tmap.get(tid)
            if not thread:
                # skip old junk (left-overs from a fork)
                continue
            P(f'{thread.name}')
            P(sep)
            traceback.print_stack(frame, file=out)
            P(sep)
            P('LOCAL VARIABLES')
            P(sep)
            pprint(frame.f_locals, stream=out)
            P('\n')
        return out.getvalue()