Limit python script RAM usage in Windows

Question

My program can allocate suddenly a lot of RAM based on usage. I want to limit the RAM it can take from the system.

I saw here: Limit RAM usage to python program

But it works only for Unix. Any solution for Windows?

Answer 1

A Job object supports limiting the committed memory of a process. In Python, we can implement this via PyWin32 or ctypes.

Note that prior to Windows 8 a process can only be in a single Job. A couple of common cases where this is a concern include the py.exe launcher (the default association for .py files), which runs python.exe in a Job, and the Task Scheduler service, which runs each task in a Job.

PyWin32 Example

import sys
import warnings

import winerror
import win32api
import win32job

g_hjob = None

def create_job(job_name='', breakaway='silent'):
    hjob = win32job.CreateJobObject(None, job_name)
    if breakaway:
        info = win32job.QueryInformationJobObject(hjob,
                    win32job.JobObjectExtendedLimitInformation)
        if breakaway == 'silent':
            info['BasicLimitInformation']['LimitFlags'] |= (
                win32job.JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK)
        else:
            info['BasicLimitInformation']['LimitFlags'] |= (
                win32job.JOB_OBJECT_LIMIT_BREAKAWAY_OK)
        win32job.SetInformationJobObject(hjob,
            win32job.JobObjectExtendedLimitInformation, info)
    return hjob

def assign_job(hjob):
    global g_hjob
    hprocess = win32api.GetCurrentProcess()
    try:
        win32job.AssignProcessToJobObject(hjob, hprocess)
        g_hjob = hjob
    except win32job.error as e:
        if (e.winerror != winerror.ERROR_ACCESS_DENIED or
            sys.getwindowsversion() >= (6, 2) or
            not win32job.IsProcessInJob(hprocess, None)):
            raise
        warnings.warn('The process is already in a job. Nested jobs are not '
            'supported prior to Windows 8.')

def limit_memory(memory_limit):
    if g_hjob is None:
        return
    info = win32job.QueryInformationJobObject(g_hjob,
                win32job.JobObjectExtendedLimitInformation)
    info['ProcessMemoryLimit'] = memory_limit
    info['BasicLimitInformation']['LimitFlags'] |= (
        win32job.JOB_OBJECT_LIMIT_PROCESS_MEMORY)
    win32job.SetInformationJobObject(g_hjob,
        win32job.JobObjectExtendedLimitInformation, info)

def main():
    assign_job(create_job())
    memory_limit = 100 * 1024 * 1024 # 100 MiB
    limit_memory(memory_limit)
    try:
        bytearray(memory_limit)
    except MemoryError:
        print('Success: available memory is limited.')
    else:
        print('Failure: available memory is not limited.')
    return 0

if __name__ == '__main__':
    sys.exit(main())

Answer 2

I had about the same problem as the OP, except that I wanted to limit the amount of physical RAM used, not virtual. @eryksun's answer and limit_memory() function work great, but limit the total amount of allocatable memory (virtual memory). Here is an additional function to his/her code that limits the amount of physical memory (the "working set").

def limit_working_set(memory_limit):
    if g_hjob is None:
        return
    info = win32job.QueryInformationJobObject(g_hjob, win32job.JobObjectBasicLimitInformation)
    info['MinimumWorkingSetSize'] = 50 * 4096  # default minimum value
    info['MaximumWorkingSetSize'] = memory_limit
    info['LimitFlags'] = (win32job.JOB_OBJECT_LIMIT_WORKINGSET)
    win32job.SetInformationJobObject(g_hjob, win32job.JobObjectBasicLimitInformation, info)