Function cpu_count

dask/system.py:46–89

Get the available CPU count for this system. Takes the minimum value from the following locations: - Total system cpus available on the host. - CPU Affinity (if set) - Cgroups limit (if set)

()

def cpu_count() -> int:
    """Get the available CPU count for this system.

    Takes the minimum value from the following locations:

    - Total system cpus available on the host.
    - CPU Affinity (if set)
    - Cgroups limit (if set)
    """
    if sys.version_info >= (3, 13):
        # Embeds CPU affinity checks
        count = os.process_cpu_count()
    elif hasattr(os, "sched_getaffinity"):
        # https://docs.python.org/3/library/os.html#interface-to-the-scheduler
        # "only available on some Unix platforms"; neither MacOS nor Windows
        count = len(os.sched_getaffinity(0))
    else:
        # Does not account for CPU affinity.
        # On exotic alternative Python implementations, it may return None.
        count = os.cpu_count() or 1
    assert count

    # Additional CPU affinity check with psutil.
    # NOTE: do not limit this to Python <3.13: on Windows,
    # `psutil.Process().cpu_affinity(value)` does not change the reading of
    # os.process_cpu_count().
    if psutil is not None:
        proc = psutil.Process()
        if hasattr(proc, "cpu_affinity"):
            affinity = proc.cpu_affinity()
            if affinity is not None:
                assert affinity
                count = min(count, len(affinity))

    # Check cgroups if available
    if LINUX:
        quota, period = _try_extract_cgroup_cpu_quota()
        if quota is not None and period is not None:
            # We round up on fractional CPUs
            cgroups_count = math.ceil(quota / period)
            if cgroups_count > 0:
                count = min(count, cgroups_count)

    return count


CPU_COUNT = cpu_count()