launch.py

"""Launching tool for DGL distributed training"""
import os
import stat
import sys
import subprocess
import argparse
import signal
import logging
import time
import json
import multiprocessing
import re
from functools import partial
from threading import Thread
from typing import Optional

def cleanup_proc(get_all_remote_pids, conn):
    '''This process tries to clean up the remote training tasks.
    '''
    print('cleanupu process runs')
    # This process should not handle SIGINT.
    signal.signal(signal.SIGINT, signal.SIG_IGN)

    data = conn.recv()
    # If the launch process exits normally, this process doesn't need to do anything.
    if data == 'exit':
        sys.exit(0)
    else:
        remote_pids = get_all_remote_pids()
        # Otherwise, we need to ssh to each machine and kill the training jobs.
        for (ip, port), pids in remote_pids.items():
            kill_process(ip, port, pids)
    print('cleanup process exits')

def kill_process(ip, port, pids):
    '''ssh to a remote machine and kill the specified processes.
    '''
    curr_pid = os.getpid()
    killed_pids = []
    # If we kill child processes first, the parent process may create more again. This happens
    # to Python's process pool. After sorting, we always kill parent processes first.
    pids.sort()
    for pid in pids:
        assert curr_pid != pid
        print('kill process {} on {}:{}'.format(pid, ip, port), flush=True)
        kill_cmd = 'ssh -o StrictHostKeyChecking=no -p ' + str(port) + ' ' + ip + ' \'kill {}\''.format(pid)
        subprocess.run(kill_cmd, shell=True)
        killed_pids.append(pid)
    # It's possible that some of the processes are not killed. Let's try again.
    for i in range(3):
        killed_pids = get_killed_pids(ip, port, killed_pids)
        if len(killed_pids) == 0:
            break
        else:
            killed_pids.sort()
            for pid in killed_pids:
                print('kill process {} on {}:{}'.format(pid, ip, port), flush=True)
                kill_cmd = 'ssh -o StrictHostKeyChecking=no -p ' + str(port) + ' ' + ip + ' \'kill -9 {}\''.format(pid)
                subprocess.run(kill_cmd, shell=True)

def get_killed_pids(ip, port, killed_pids):
    '''Get the process IDs that we want to kill but are still alive.
    '''
    killed_pids = [str(pid) for pid in killed_pids]
    killed_pids = ','.join(killed_pids)
    ps_cmd = 'ssh -o StrictHostKeyChecking=no -p ' + str(port) + ' ' + ip + ' \'ps -p {} -h\''.format(killed_pids)
    res = subprocess.run(ps_cmd, shell=True, stdout=subprocess.PIPE)
    pids = []
    for p in res.stdout.decode('utf-8').split('\n'):
        l = p.split()
        if len(l) > 0:
            pids.append(int(l[0]))
    return pids

def execute_remote(
    cmd: str,
    ip: str,
    port: int,
    username: Optional[str] = ""
) -> Thread:
    """Execute command line on remote machine via ssh.

    Args:
        cmd: User-defined command (udf) to execute on the remote host.
        ip: The ip-address of the host to run the command on.
        port: Port number that the host is listening on.
        thread_list:
        username: Optional. If given, this will specify a username to use when issuing commands over SSH.
            Useful when your infra requires you to explicitly specify a username to avoid permission issues.

    Returns:
        thread: The Thread whose run() is to run the `cmd` on the remote host. Returns when the cmd completes
            on the remote host.
    """
    ip_prefix = ""
    if username:
        ip_prefix += "{username}@".format(username=username)

    # Construct ssh command that executes `cmd` on the remote host
    ssh_cmd = "ssh -o StrictHostKeyChecking=no -p {port} {ip_prefix}{ip} '{cmd}'".format(
        port=str(port),
        ip_prefix=ip_prefix,
        ip=ip,
        cmd=cmd,
    )

    # thread func to run the job
    def run(ssh_cmd):
        subprocess.check_call(ssh_cmd, shell=True)

    thread = Thread(target=run, args=(ssh_cmd,))
    thread.setDaemon(True)
    thread.start()
    return thread

def get_remote_pids(ip, port, cmd_regex):
    """Get the process IDs that run the command in the remote machine.
    """
    pids = []
    curr_pid = os.getpid()
    # Here we want to get the python processes. We may get some ssh processes, so we should filter them out.
    ps_cmd = 'ssh -o StrictHostKeyChecking=no -p ' + str(port) + ' ' + ip + ' \'ps -aux | grep python | grep -v StrictHostKeyChecking\''
    res = subprocess.run(ps_cmd, shell=True, stdout=subprocess.PIPE)
    for p in res.stdout.decode('utf-8').split('\n'):
        l = p.split()
        if len(l) < 2:
            continue
        # We only get the processes that run the specified command.
        res = re.search(cmd_regex, p)
        if res is not None and int(l[1]) != curr_pid:
            pids.append(l[1])

    pid_str = ','.join([str(pid) for pid in pids])
    ps_cmd = 'ssh -o StrictHostKeyChecking=no -p ' + str(port) + ' ' + ip + ' \'pgrep -P {}\''.format(pid_str)
    res = subprocess.run(ps_cmd, shell=True, stdout=subprocess.PIPE)
    pids1 = res.stdout.decode('utf-8').split('\n')
    all_pids = []
    for pid in set(pids + pids1):
        if pid == '' or int(pid) == curr_pid:
            continue
        all_pids.append(int(pid))
    all_pids.sort()
    return all_pids

def get_all_remote_pids(hosts, ssh_port, udf_command):
    '''Get all remote processes.
    '''
    remote_pids = {}
    for node_id, host in enumerate(hosts):
        ip, _ = host
        # When creating training processes in remote machines, we may insert some arguments
        # in the commands. We need to use regular expressions to match the modified command.
        cmds = udf_command.split()
        new_udf_command = ' .*'.join(cmds)
        pids = get_remote_pids(ip, ssh_port, new_udf_command)
        remote_pids[(ip, ssh_port)] = pids
    return remote_pids


def construct_torch_dist_launcher_cmd(
    num_trainers: int,
    num_nodes: int,
    node_rank: int,
    master_addr: str,
    master_port: int
) -> str:
    """Constructs the torch distributed launcher command.
    Helper function.

    Args:
        num_trainers:
        num_nodes:
        node_rank:
        master_addr:
        master_port:

    Returns:
        cmd_str.
    """
    torch_cmd_template = "-m torch.distributed.launch " \
                         "--nproc_per_node={nproc_per_node} " \
                         "--nnodes={nnodes} " \
                         "--node_rank={node_rank} " \
                         "--master_addr={master_addr} " \
                         "--master_port={master_port}"
    return torch_cmd_template.format(
        nproc_per_node=num_trainers,
        nnodes=num_nodes,
        node_rank=node_rank,
        master_addr=master_addr,
        master_port=master_port
    )


def wrap_udf_in_torch_dist_launcher(
    udf_command: str,
    num_trainers: int,
    num_nodes: int,
    node_rank: int,
    master_addr: str,
    master_port: int,
) -> str:
    """Wraps the user-defined function (udf_command) with the torch.distributed.launch module.

     Example: if udf_command is "python3 run/some/trainer.py arg1 arg2", then new_df_command becomes:
         "python3 -m torch.distributed.launch <TORCH DIST ARGS> run/some/trainer.py arg1 arg2

    udf_command is assumed to consist of pre-commands (optional) followed by the python launcher script (required):
    Examples:
        # simple
        python3.7 path/to/some/trainer.py arg1 arg2

        # multi-commands
        (cd some/dir && python3.7 path/to/some/trainer.py arg1 arg2)

    IMPORTANT: If udf_command consists of multiple python commands, then this will result in undefined behavior.

    Args:
        udf_command:
        num_trainers:
        num_nodes:
        node_rank:
        master_addr:
        master_port:

    Returns:

    """
    torch_dist_cmd = construct_torch_dist_launcher_cmd(
        num_trainers=num_trainers,
        num_nodes=num_nodes,
        node_rank=node_rank,
        master_addr=master_addr,
        master_port=master_port
    )
    # Auto-detect the python binary that kicks off the distributed trainer code.
    # Note: This allowlist order matters, this will match with the FIRST matching entry. Thus, please add names to this
    #       from most-specific to least-specific order eg:
    #           (python3.7, python3.8) -> (python3)
    # The allowed python versions are from this: https://www.dgl.ai/pages/start.html
    python_bin_allowlist = (
        "python3.6", "python3.7", "python3.8", "python3.9", "python3",
        # for backwards compatibility, accept python2 but technically DGL is a py3 library, so this is not recommended
        "python2.7", "python2",
    )
    # If none of the candidate python bins match, then we go with the default `python`
    python_bin = "python"
    for candidate_python_bin in python_bin_allowlist:
        if candidate_python_bin in udf_command:
            python_bin = candidate_python_bin
            break

    # transforms the udf_command from:
    #     python path/to/dist_trainer.py arg0 arg1
    # to:
    #     python -m torch.distributed.launch [DIST TORCH ARGS] path/to/dist_trainer.py arg0 arg1
    # Note: if there are multiple python commands in `udf_command`, this may do the Wrong Thing, eg launch each
    #       python command within the torch distributed launcher.
    new_udf_command = udf_command.replace(python_bin, f"{python_bin} {torch_dist_cmd}")

    return new_udf_command


def construct_dgl_server_env_vars(
    num_samplers: int,
    num_server_threads: int,
    tot_num_clients: int,
    part_config: str,
    ip_config: str,
    num_servers: int,
    graph_format: str,
    keep_alive: bool,
    pythonpath: Optional[str] = "",
) -> str:
    """Constructs the DGL server-specific env vars string that are required for DGL code to behave in the correct
    server role.
    Convenience function.

    Args:
        num_samplers:
        num_server_threads:
        tot_num_clients:
        part_config: Partition config.
            Relative path to workspace.
        ip_config: IP config file containing IP addresses of cluster hosts.
            Relative path to workspace.
        num_servers:
        graph_format:
        keep_alive:
            Whether to keep server alive when clients exit
        pythonpath: Optional. If given, this will pass this as PYTHONPATH.

    Returns:
        server_env_vars: The server-specific env-vars in a string format, friendly for CLI execution.

    """
    server_env_vars_template = (
        "DGL_ROLE={DGL_ROLE} "
        "DGL_NUM_SAMPLER={DGL_NUM_SAMPLER} "
        "OMP_NUM_THREADS={OMP_NUM_THREADS} "
        "DGL_NUM_CLIENT={DGL_NUM_CLIENT} "
        "DGL_CONF_PATH={DGL_CONF_PATH} "
        "DGL_IP_CONFIG={DGL_IP_CONFIG} "
        "DGL_NUM_SERVER={DGL_NUM_SERVER} "
        "DGL_GRAPH_FORMAT={DGL_GRAPH_FORMAT} "
        "DGL_KEEP_ALIVE={DGL_KEEP_ALIVE} "
        "{suffix_optional_envvars}"
    )
    suffix_optional_envvars = ""
    if pythonpath:
        suffix_optional_envvars += f"PYTHONPATH={pythonpath} "
    return server_env_vars_template.format(
        DGL_ROLE="server",
        DGL_NUM_SAMPLER=num_samplers,
        OMP_NUM_THREADS=num_server_threads,
        DGL_NUM_CLIENT=tot_num_clients,
        DGL_CONF_PATH=part_config,
        DGL_IP_CONFIG=ip_config,
        DGL_NUM_SERVER=num_servers,
        DGL_GRAPH_FORMAT=graph_format,
        DGL_KEEP_ALIVE=int(keep_alive),
        suffix_optional_envvars=suffix_optional_envvars,
    )


def construct_dgl_client_env_vars(
    num_samplers: int,
    tot_num_clients: int,
    part_config: str,
    ip_config: str,
    num_servers: int,
    graph_format: str,
    num_omp_threads: int,
    group_id: int,
    pythonpath: Optional[str] = "",
) -> str:
    """Constructs the DGL client-specific env vars string that are required for DGL code to behave in the correct
    client role.
    Convenience function.

    Args:
        num_samplers:
        tot_num_clients:
        part_config: Partition config.
            Relative path to workspace.
        ip_config: IP config file containing IP addresses of cluster hosts.
            Relative path to workspace.
        num_servers:
        graph_format:
        num_omp_threads:
        group_id:
            Used in client processes to indicate which group it belongs to.
        pythonpath: Optional. If given, this will pass this as PYTHONPATH.

    Returns:
        client_env_vars: The client-specific env-vars in a string format, friendly for CLI execution.

    """
    client_env_vars_template = (
        "DGL_DIST_MODE={DGL_DIST_MODE} "
        "DGL_ROLE={DGL_ROLE} "
        "DGL_NUM_SAMPLER={DGL_NUM_SAMPLER} "
        "DGL_NUM_CLIENT={DGL_NUM_CLIENT} "
        "DGL_CONF_PATH={DGL_CONF_PATH} "
        "DGL_IP_CONFIG={DGL_IP_CONFIG} "
        "DGL_NUM_SERVER={DGL_NUM_SERVER} "
        "DGL_GRAPH_FORMAT={DGL_GRAPH_FORMAT} "
        "OMP_NUM_THREADS={OMP_NUM_THREADS} "
        "DGL_GROUP_ID={DGL_GROUP_ID} "
        "{suffix_optional_envvars}"
    )
    # append optional additional env-vars
    suffix_optional_envvars = ""
    if pythonpath:
        suffix_optional_envvars += f"PYTHONPATH={pythonpath} "
    return client_env_vars_template.format(
        DGL_DIST_MODE="distributed",
        DGL_ROLE="client",
        DGL_NUM_SAMPLER=num_samplers,
        DGL_NUM_CLIENT=tot_num_clients,
        DGL_CONF_PATH=part_config,
        DGL_IP_CONFIG=ip_config,
        DGL_NUM_SERVER=num_servers,
        DGL_GRAPH_FORMAT=graph_format,
        OMP_NUM_THREADS=num_omp_threads,
        DGL_GROUP_ID=group_id,
        suffix_optional_envvars=suffix_optional_envvars,
    )


def wrap_cmd_with_local_envvars(cmd: str, env_vars: str) -> str:
    """Wraps a CLI command with desired env vars with the following properties:
    (1) env vars persist for the entire `cmd`, even if it consists of multiple "chained" commands like:
        cmd = "ls && pwd && python run/something.py"
    (2) env vars don't pollute the environment after `cmd` completes.

    Example:
        >>> cmd = "ls && pwd"
        >>> env_vars = "VAR1=value1 VAR2=value2"
        >>> wrap_cmd_with_local_envvars(cmd, env_vars)
        "(export VAR1=value1 VAR2=value2; ls && pwd)"

    Args:
        cmd:
        env_vars: A string containing env vars, eg "VAR1=val1 VAR2=val2"

    Returns:
        cmd_with_env_vars:

    """
    # use `export` to persist env vars for entire cmd block. required if udf_command is a chain of commands
    # also: wrap in parens to not pollute env:
    #     https://stackoverflow.com/a/45993803
    return f"(export {env_vars}; {cmd})"

def wrap_cmd_with_extra_envvars(cmd: str, env_vars: list) -> str:
    """Wraps a CLI command with extra env vars

    Example:
        >>> cmd = "ls && pwd"
        >>> env_vars = ["VAR1=value1", "VAR2=value2"]
        >>> wrap_cmd_with_extra_envvars(cmd, env_vars)
        "(export VAR1=value1 VAR2=value2; ls && pwd)"

    Args:
        cmd:
        env_vars: A list of strings containing env vars, e.g., ["VAR1=value1", "VAR2=value2"]

    Returns:
        cmd_with_env_vars:
    """
    env_vars = " ".join(env_vars)
    return wrap_cmd_with_local_envvars(cmd, env_vars)


g_monitor_file = None
g_group_id = 0

def has_alive_servers(args):
    """Check whether there exists alive servers.

    For each group of long live servers, a monitor file named
    'dgl_dist_monitor_{args.server_name}' is created under '/tmp/' directory.
    We check the existence of this monitor file to determine whether to
    launch new servers or utilize the existing alive ones. If there
    exist alive servers, we obtain availale group ID from the monitor
    file which could be used in current client groups.

    Returns
    -------
    bool
        indicates whether there exists alive servers.
    """
    if args.server_name is None:
        return False
    global g_monitor_file
    global g_group_id
    monitor_file = '/tmp/dgl_dist_monitor_' + args.server_name
    from filelock import FileLock
    lock = FileLock(monitor_file + '.lock')
    with lock:
        next_group_id = None
        ret = os.path.exists(monitor_file)
        if ret:
            print("Monitor file for alive servers already exist: {}.".format(monitor_file))
            lines = [line.rstrip('\n') for line in open(monitor_file)]
            g_group_id = int(lines[0])
            next_group_id = g_group_id + 1
        if not ret and args.keep_alive:
            next_group_id = 1
            print("Monitor file for alive servers is created: {}.".format(monitor_file))
            g_monitor_file = monitor_file
        if next_group_id is not None:
            with open(monitor_file, 'w') as f:
                f.write(str(next_group_id))
    return ret


def clean_alive_servers():
    """Remove keep alive related files"""
    global g_monitor_file
    try:
        if g_monitor_file is not None:
            os.remove(g_monitor_file)
            os.remove(g_monitor_file + '.lock')
            print("Monitor file for alive servers is removed: {}.".format(g_monitor_file))
    except:
        print("Failed to delete monitor file for alive servers: {}.".format(g_monitor_file))

def get_available_port(ip):
    """Get available port with specified ip."""
    import socket
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    for port in range(1234, 65535):
        try:
            sock.connect((ip, port))
        except:
            return port
    raise RuntimeError("Failed to get available port for ip~{}".format(ip))

def submit_jobs(args, udf_command):
    """Submit distributed jobs (server and client processes) via ssh"""
    hosts = []
    thread_list = []
    server_count_per_machine = 0

    # Get the IP addresses of the cluster.
    ip_config = os.path.join(args.workspace, args.ip_config)
    with open(ip_config) as f:
        for line in f:
            result = line.strip().split()
            if len(result) == 2:
                ip = result[0]
                port = int(result[1])
                hosts.append((ip, port))
            elif len(result) == 1:
                ip = result[0]
                port = get_available_port(ip)
                hosts.append((ip, port))
            else:
                raise RuntimeError("Format error of ip_config.")
            server_count_per_machine = args.num_servers
    # Get partition info of the graph data
    part_config = os.path.join(args.workspace, args.part_config)
    with open(part_config) as conf_f:
        part_metadata = json.load(conf_f)
    assert 'num_parts' in part_metadata, 'num_parts does not exist.'
    # The number of partitions must match the number of machines in the cluster.
    assert part_metadata['num_parts'] == len(hosts), \
            'The number of graph partitions has to match the number of machines in the cluster.'

    tot_num_clients = args.num_trainers * (1 + args.num_samplers) * len(hosts)
    # launch server tasks
    if not has_alive_servers(args):
        server_env_vars = construct_dgl_server_env_vars(
            num_samplers=args.num_samplers,
            num_server_threads=args.num_server_threads,
            tot_num_clients=tot_num_clients,
            part_config=args.part_config,
            ip_config=args.ip_config,
            num_servers=args.num_servers,
            graph_format=args.graph_format,
            keep_alive=args.keep_alive,
            pythonpath=os.environ.get("PYTHONPATH", ""),
        )
        for i in range(len(hosts) * server_count_per_machine):
            ip, _ = hosts[int(i / server_count_per_machine)]
            server_env_vars_cur = f"{server_env_vars} DGL_SERVER_ID={i}"
            cmd = wrap_cmd_with_local_envvars(udf_command, server_env_vars_cur)
            cmd = wrap_cmd_with_extra_envvars(cmd, args.extra_envs) if len(args.extra_envs) > 0 else cmd
            cmd = 'cd ' + str(args.workspace) + '; ' + cmd
            thread_list.append(execute_remote(cmd, ip, args.ssh_port, username=args.ssh_username))
    else:
        print(f"Use running server {args.server_name}.")

    # launch client tasks
    client_env_vars = construct_dgl_client_env_vars(
        num_samplers=args.num_samplers,
        tot_num_clients=tot_num_clients,
        part_config=args.part_config,
        ip_config=args.ip_config,
        num_servers=args.num_servers,
        graph_format=args.graph_format,
        num_omp_threads=os.environ.get("OMP_NUM_THREADS", str(args.num_omp_threads)),
        group_id=g_group_id,
        pythonpath=os.environ.get("PYTHONPATH", ""),
    )

    for node_id, host in enumerate(hosts):
        ip, _ = host
        # Transform udf_command to follow torch's dist launcher format: `PYTHON_BIN -m torch.distributed.launch ... UDF`
        torch_dist_udf_command = wrap_udf_in_torch_dist_launcher(
            udf_command=udf_command,
            num_trainers=args.num_trainers,
            num_nodes=len(hosts),
            node_rank=node_id,
            master_addr=hosts[0][0],
            master_port=get_available_port(hosts[0][0]),
        )
        cmd = wrap_cmd_with_local_envvars(torch_dist_udf_command, client_env_vars)
        cmd = wrap_cmd_with_extra_envvars(cmd, args.extra_envs) if len(args.extra_envs) > 0 else cmd
        cmd = 'cd ' + str(args.workspace) + '; ' + cmd
        thread_list.append(execute_remote(cmd, ip, args.ssh_port, username=args.ssh_username))

    # Start a cleanup process dedicated for cleaning up remote training jobs.
    conn1,conn2 = multiprocessing.Pipe()
    func = partial(get_all_remote_pids, hosts, args.ssh_port, udf_command)
    process = multiprocessing.Process(target=cleanup_proc, args=(func, conn1))
    process.start()

    def signal_handler(signal, frame):
        logging.info('Stop launcher')
        # We need to tell the cleanup process to kill remote training jobs.
        conn2.send('cleanup')
        clean_alive_servers()
        sys.exit(0)
    signal.signal(signal.SIGINT, signal_handler)

    for thread in thread_list:
        thread.join()
    # The training processes complete. We should tell the cleanup process to exit.
    conn2.send('exit')
    process.join()


def main():
    parser = argparse.ArgumentParser(description='Launch a distributed job')
    parser.add_argument('--ssh_port', type=int, default=22, help='SSH Port.')
    parser.add_argument(
        "--ssh_username", default="",
        help="Optional. When issuing commands (via ssh) to cluster, use the provided username in the ssh cmd. "
             "Example: If you provide --ssh_username=bob, then the ssh command will be like: 'ssh bob@1.2.3.4 CMD' "
             "instead of 'ssh 1.2.3.4 CMD'"
    )
    parser.add_argument('--workspace', type=str,
                        help='Path of user directory of distributed tasks. \
                        This is used to specify a destination location where \
                        the contents of current directory will be rsyncd')
    parser.add_argument('--num_trainers', type=int,
                        help='The number of trainer processes per machine')
    parser.add_argument('--num_omp_threads', type=int,
                        help='The number of OMP threads per trainer')
    parser.add_argument('--num_samplers', type=int, default=0,
                        help='The number of sampler processes per trainer process')
    parser.add_argument('--num_servers', type=int,
                        help='The number of server processes per machine')
    parser.add_argument('--part_config', type=str,
                        help='The file (in workspace) of the partition config')
    parser.add_argument('--ip_config', type=str,
                        help='The file (in workspace) of IP configuration for server processes')
    parser.add_argument('--num_server_threads', type=int, default=1,
                        help='The number of OMP threads in the server process. \
                        It should be small if server processes and trainer processes run on \
                        the same machine. By default, it is 1.')
    parser.add_argument('--graph_format', type=str, default='csc',
                        help='The format of the graph structure of each partition. \
                        The allowed formats are csr, csc and coo. A user can specify multiple \
                        formats, separated by ",". For example, the graph format is "csr,csc".')
    parser.add_argument('--extra_envs', nargs='+', type=str, default=[],
                        help='Extra environment parameters need to be set. For example, \
                        you can set the LD_LIBRARY_PATH and NCCL_DEBUG by adding: \
                        --extra_envs LD_LIBRARY_PATH=/usr/local/cuda/lib64:$LD_LIBRARY_PATH NCCL_DEBUG=INFO ')
    parser.add_argument('--keep_alive', action='store_true', help='Servers keep alive when clients exit')
    parser.add_argument('--server_name', type=str,
                        help='Used to check whether there exist alive servers')
    args, udf_command = parser.parse_known_args()
    if args.keep_alive:
        assert args.server_name is not None, "Server name is required if '--keep_alive' is enabled."
        print("Servers will keep alive even clients exit...")
    assert len(udf_command) == 1, 'Please provide user command line.'
    assert args.num_trainers is not None and args.num_trainers > 0, \
            '--num_trainers must be a positive number.'
    assert args.num_samplers is not None and args.num_samplers >= 0, \
            '--num_samplers must be a non-negative number.'
    assert args.num_servers is not None and args.num_servers > 0, \
            '--num_servers must be a positive number.'
    assert args.num_server_threads > 0, '--num_server_threads must be a positive number.'
    assert args.workspace is not None, 'A user has to specify a workspace with --workspace.'
    assert args.part_config is not None, \
            'A user has to specify a partition configuration file with --part_config.'
    assert args.ip_config is not None, \
            'A user has to specify an IP configuration file with --ip_config.'
    if args.num_omp_threads is None:
        # Here we assume all machines have the same number of CPU cores as the machine
        # where the launch script runs.
        args.num_omp_threads = max(multiprocessing.cpu_count() // 2 // args.num_trainers, 1)
        print('The number of OMP threads per trainer is set to', args.num_omp_threads)

    udf_command = str(udf_command[0])
    if 'python' not in udf_command:
        raise RuntimeError("DGL launching script can only support Python executable file.")
    submit_jobs(args, udf_command)

if __name__ == '__main__':
    fmt = '%(asctime)s %(levelname)s %(message)s'
    logging.basicConfig(format=fmt, level=logging.INFO)
    main()