multiprocessing_name.py

class ProcessNameSetter:
    instance = None

    @classmethod
    def register(cls):
        if cls.instance is not None:
            return
        try:
            cls.instance = cls()
            import multiprocessing.util
            multiprocessing.util.register_after_fork(cls.instance, cls.afterfork)
        except:
            import traceback
            traceback.print_exc()

    def afterfork(self):
        import procname, multiprocessing
        procname.set_process_name('pymp:' + multiprocessing.current_process().name)

ProcessNameSetter.register()

procname.py

import ctypes, sys

def get_orig_argv():
    result = getattr(sys, 'orig_argv', None)
    if result is not None:
        return result

    _argv = ctypes.POINTER(ctypes.c_wchar_p)()
    _argc = ctypes.c_int()

    ctypes.pythonapi.Py_GetArgcArgv(ctypes.byref(_argc), ctypes.byref(_argv))

    argv = _argv[:_argc.value]
    return argv

ARG_MAX = 96 * 1024

c_size_t_p = ctypes.POINTER(ctypes.c_size_t)
RTLD_DEFAULT = ctypes.CDLL(None, handle=0) # RTLD_DEFAULT = 0

deref = lambda p: ctypes.c_ubyte.from_address(p).value

def get_argv_buf():
    argv = get_orig_argv()

    ptr = c_size_t_p.in_dll(RTLD_DEFAULT, 'environ') # dlsym(RTLD_DEFAULT, "environ")
    ptr = ptr.contents.value

    limit = ptr - ARG_MAX
    ptr -= 1
    upper = ptr

    #buf = [None] * len(argv)
    for i in range(len(argv) - 1, 0, -1):
        if deref(ptr) != 0:
            #print(f'zero {i} not found')
            return None, None
        ptr -= 1
        while deref(ptr) != 0 and ptr > limit: ptr -= 1
        if ptr <= limit:
            #print(f'failed to found arg {i} start')
            return None, None
        #buf[i] = ptr + 1
        #print(f'found argv[{i}] at {buf[i]}: {ctypes.string_at(buf[i])}')

    ptr -= len(argv[0])
    argv0 = ctypes.string_at(ptr)
    #print(f'argv[0] should be at {ptr}: {argv0}')
    if argv0 != argv[0].encode():
        #print(f'argv[0] "{argv0}" doesn\'t match "{argv[0]}"')
        return None, None

    #buf[0] = ptr
    return ptr, upper - ptr

argv_ptr = None
argv_size = None

def set_process_name(name):
    global argv_ptr, argv_size
    if not argv_ptr:
        argv_ptr, argv_size = get_argv_buf()
        if not argv_ptr: return
    if isinstance(name, str):
        name = name.encode()
    ctypes.memset(argv_ptr, 0, argv_size)
    ctypes.memmove(argv_ptr, name, min(len(name), argv_size))