python_pinger.git

first commit.
David Blume

David Blume commited on 2019-07-05 20:08:07
Showing 9 changed files, with 339 additions and 0 deletions.

LICENSE.txt
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+The MIT License (MIT)
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+
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+Copyright (c) 2019 David Blume
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+
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+Permission is hereby granted, free of charge, to any person obtaining a copy
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+of this software and associated documentation files (the "Software"), to deal
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+in the Software without restriction, including without limitation the rights
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+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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+copies of the Software, and to permit persons to whom the Software is
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+furnished to do so, subject to the following conditions:
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+
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+The above copyright notice and this permission notice shall be included in all
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+copies or substantial portions of the Software.
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+
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+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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+SOFTWARE.
README.md
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+# python_pinger
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+
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+These are different approaches to how one might implement a daemon to
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+repeatedly ping multiple hosts to see if the network is up.
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+
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+## Single Threaded
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+
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+This is the most naive implementation. For each ping host, the main
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+process thread pings them one at a time, and prints any changes.
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+
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+![Single Threaded Pings](http://git.dlma.com/python_pinger.git/blob/master/images/ping_single_threaded.png)
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+
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+### Upsides
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+
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+Really simple code.
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+
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+### Downsides
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+
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+Since the pings are serialized, one long timeout from one host could
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+affect detecting a problem at another host.
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+
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+## Long Lived Workers Consuming from Queue
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+
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+Raymond Hettinger's [PyBay 2018 Keynote](https://pybay.com/site_media/slides/raymond2017-keynote/threading.html)
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+uses the queue module to send data between threads, so I thought I'd make a version of the pinger that did the same.
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+
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+[long\_lived\_worker\_queue.py](http://git.dlma.com/python_pinger.git/blob/master/long_lived_worker_queue.py)
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+
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+![Long Lived Queue Workers](http://git.dlma.com/python_pinger.git/blob/master/images/ping_long_lived_queue_workers.png)
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+
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+### Upsides
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+
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+Multi-threaded ping calls won't block each other.
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+
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+### Downsides
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+
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+The ping tasks read from, and write to a shared dictionary. (Reading and updating the last status.)
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+
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+## Short Lived Workers
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+
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+![Short Lived Workers](http://git.dlma.com/python_pinger.git/blob/master/images/ping_short_lived_workers.png)
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+
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+[short\_lived\_workers.py](http://git.dlma.com/python_pinger.git/blob/master/short_lived_workers.py)
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+
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+### Upsides
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+
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+The worker tasks aren't in memory if they're not doing anything. So usually a smaller memory profile.
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+
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+### Downsides
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+
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+The ping tasks still read from, and write to a shared dictionary. (Reading and updating the last status.)
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+
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+## Long Lived Looping Workers
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+
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+![Long Lived Looping Workers](http://git.dlma.com/python_pinger.git/blob/master/images/ping_long_lived_looping_workers.png)
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+
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+[long\_lived\_looping\_workers.py](http://git.dlma.com/python_pinger.git/blob/master/long_lived_looping_workers.py)
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+
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+### Upsides
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+
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+No more race conditions! The worker threads mind their own business.
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+
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+### Downsides
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+
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+The worker threads remain in memory.
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+
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+## Is it any good?
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+
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+[Yes](https://news.ycombinator.com/item?id=3067434).
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+
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+## Licence
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+
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+This software uses the [MIT license](http://git.dlma.com/python_pinger.git/blob/master/LICENSE.txt).
images/ping_long_lived_looping_workers.png
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images/ping_long_lived_queue_workers.png
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images/ping_short_lived_workers.png
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images/ping_single_threaded.png
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long_lived_looping_workers.py
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+#!/usr/bin/python3
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+#
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+# Since this is meant to be run as a daemon, do not use #!/usr/bin/env python3,
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+# because the process name would then be python3, not based on __FILE__.
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+#
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+# [filename] -d 3 192.168.1.1 192.168.1.12 &
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+# disown [jobid]
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+import os
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+import sys
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+import subprocess
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+import time
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+from argparse import ArgumentParser
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+import threading
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+import queue
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+
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+
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+def pinger(host, delay):
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+    """Independent worker thread: repeatedly ping, check, print and sleep."""
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+    last_results = None
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+    while True:
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+        now = time.localtime()
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+        success = ping(host)
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+        if success != last_results:
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+            status = "UP" if success else "DOWN"
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+            _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", now)} {host} {status}'])
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+            last_results = success
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+        time.sleep(delay)
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+
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+
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+def ping(host):
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+    """Returns True if host (str) responds to a ping request."""
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+    return subprocess.call([*_ping_cmd, host], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL) == 0
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+
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+
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+def print_manager():
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+    """The only thread allowed to write output."""
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+    while True:
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+        job = _print_queue.get()
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+        for line in job:
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+            log(line)
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+        _print_queue.task_done()
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+
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+
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+def log(*args, **kwargs):
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+    """Opens the logfile, writes the log, and closes the logfile."""
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+    # I don't leave the log file open for writing because another process needs access too.
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+    with open(_logname, 'a') as fp:
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+        return print(*args, **kwargs, file=fp)
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+
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+
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+if __name__ == '__main__':
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+    parser = ArgumentParser(description="Repeatedly ping sites. Ex: %(prog)s -d 3 192.168.1.1 192.168.1.12")
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+    parser.add_argument('-d', '--delay', type=float, default=1.0, help='Delay between pings')
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+    parser.add_argument('addresses', nargs='+', help='Addresses to ping')
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+    parser_args = parser.parse_args()
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+
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+    _logname = os.path.join(os.path.expanduser('~'), 'log', os.path.basename(sys.argv[0]).replace('py', 'txt'))
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+
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+    # Choose the ping parameters appropriate for the platform
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+    if sys.platform == 'cygwin' or sys.platform == 'win32':
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+        _ping_cmd = ('ping', '-n', '1', '-w', '2000')
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+    else:
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+        _ping_cmd = ('ping', '-c', '1', '-W', '2', '-q')
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+
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+    _print_queue = queue.Queue()
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+    print_thread = threading.Thread(target=print_manager, daemon=True)
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+    print_thread.start()
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+
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+    _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())}'
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+                      f' PID={os.getpid()} repeat={parser_args.delay}s Starting'])
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+    for address in parser_args.addresses:
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+        t = threading.Thread(target=pinger, args=(address, parser_args.delay), daemon=True)
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+        t.start()
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+        del t
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+
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+    # Stay alive forever. Join the infinitely looping print thread.
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+    print_thread.join()
long_lived_worker_queue.py
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+#!/usr/bin/python3
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+#
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+# Since this is meant to be run as a daemon, do not use #!/usr/bin/env python3,
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+# because the process name would then be python3, not based on __FILE__.
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+#
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+# [filename] -d 3 192.168.1.1 192.168.1.12 &
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+# disown [jobid]
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+import os
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+import sys
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+import subprocess
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+import time
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+from argparse import ArgumentParser
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+import threading
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+import queue
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+
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+
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+def pinger():
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+    """Each queue item is a new address to ping. Ping and compare and print.
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+    Issue: Each of these threads reads from and writes to the global _results dict.
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+    """
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+    while True:
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+        host = _ping_queue.get()
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+        now = time.localtime()
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+        success = ping(host)
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+        if success != _results[host]:
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+            status = "UP" if success else "DOWN"
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+            _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", now)} {host} {status}'])
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+            _results[host] = success
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+        _ping_queue.task_done()
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+
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+
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+def ping(host):
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+    """Returns True if host (str) responds to a ping request."""
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+    return subprocess.call([*_ping_cmd, host], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL) == 0
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+
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+
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+def print_manager():
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+    """The only thread allowed to write output."""
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+    while True:
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+        job = _print_queue.get()
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+        for line in job:
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+            log(line)
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+        _print_queue.task_done()
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+
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+
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+def log(*args, **kwargs):
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+    """Opens the logfile, writes the log, and closes the logfile."""
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+    # I don't leave the log file open for writing because another process needs access too.
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+    with open(_logname, 'a') as fp:
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+        return print(*args, **kwargs, file=fp)
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+
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+
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+if __name__ == '__main__':
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+    parser = ArgumentParser(description="Repeatedly ping sites. Ex: %(prog)s -d 3 192.168.1.1 192.168.1.12")
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+    parser.add_argument('-d', '--delay', type=float, default=1.0, help='Delay between pings')
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+    parser.add_argument('addresses', nargs='+', help='Addresses to ping')
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+    parser_args = parser.parse_args()
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+
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+    _results = dict()
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+    for addr in parser_args.addresses:
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+        _results[addr] = None
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+    delay = parser_args.delay
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+
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+    _ping_queue = queue.Queue(2 * len(parser_args.addresses))  # No more than 2 pending pings per address
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+    _print_queue = queue.Queue()
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+
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+    _logname = os.path.join(os.path.expanduser('~'), 'log', os.path.basename(sys.argv[0]).replace('py', 'txt'))
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+    _pid = os.getpid()
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+
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+    # Choose the ping parameters appropriate for the platform
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+    if sys.platform == 'cygwin' or sys.platform == 'win32':
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+        _ping_cmd = ('ping', '-n', '1', '-w', '2000')
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+    else:
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+        _ping_cmd = ('ping', '-c', '1', '-W', '2', '-q')
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+
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+    for i in range(len(parser_args.addresses)):
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+        t = threading.Thread(target=pinger, daemon=True)
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+        t.start()
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+        del t
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+
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+    t = threading.Thread(target=print_manager, daemon=True)
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+    t.start()
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+    del t
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+
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+    _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())}'
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+                      f' PID={os.getpid()} repeat={delay}s Starting'])
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+    while True:
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+        for address in _results.keys():
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+            _ping_queue.put(address)
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+        time.sleep(delay)
short_lived_workers.py
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+#!/usr/bin/python3
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+#
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+# Since this is meant to be run as a daemon, do not use #!/usr/bin/env python3,
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+# because the process name would then be python3, not based on __FILE__.
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+#
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+# [filename] -d 3 192.168.1.1 192.168.1.12 &
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+# disown [jobid]
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+import os
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+import sys
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+import subprocess
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+import time
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+from argparse import ArgumentParser
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+import threading
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+import queue
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+
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+
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+def pinger(host):
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+    """Executes one ping, prints if there was a change, exits thread."""
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+    now = time.localtime()
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+    success = ping(host)
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+    if success != _results[host]:
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+        status = "UP" if success else "DOWN"
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+        _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", now)} {host} {status}'])
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+        _results[host] = success
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+
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+
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+def ping(host):
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+    """Returns True if host (str) responds to a ping request."""
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+    return subprocess.call([*_ping_cmd, host], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL) == 0
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+
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+
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+def print_manager():
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+    """ The only thread allowed to write output. """
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+    while True:
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+        job = _print_queue.get()
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+        for line in job:
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+            log(line)
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+        _print_queue.task_done()
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+
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+
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+def log(*args, **kwargs):
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+    """Opens the logfile, writes the log, and closes the logfile."""
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+    # I don't leave the log file open for writing because another process needs access too.
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+    with open(_logname, 'a') as fp:
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+        return print(*args, **kwargs, file=fp)
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+
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+
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+if __name__ == '__main__':
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+    parser = ArgumentParser(description="Repeatedly ping sites. Ex: %(prog)s -d 3 192.168.1.1 192.168.1.12")
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+    parser.add_argument('-d', '--delay', type=float, default=1.0, help='Delay between pings')
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+    parser.add_argument('addresses', nargs='+', help='Addresses to ping')
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+    parser_args = parser.parse_args()
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+
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+    _results = dict()
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+    for addr in parser_args.addresses:
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+        _results[addr] = None
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+    delay = parser_args.delay
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+    _logname = os.path.join(os.path.expanduser('~'), 'log', os.path.basename(sys.argv[0]).replace('py', 'txt'))
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+
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+    # Choose the ping parameters appropriate for the platform
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+    if sys.platform == 'cygwin' or sys.platform == 'win32':
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+        _ping_cmd = ('ping', '-n', '1', '-w', '2000')
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+    else:
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+        _ping_cmd = ('ping', '-c', '1', '-W', '2', '-q')
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+
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+    _print_queue = queue.Queue()
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+    t = threading.Thread(target=print_manager, daemon=True)
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+    t.start()
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+    del t
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+
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+    _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())}'
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+                      f' PID={os.getpid()} repeat={delay}s Starting'])
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+    while True:
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+        for address in _results.keys():
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+            t = threading.Thread(target=pinger, args=(address,), daemon=True)
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+            t.start()
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+            del t
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+        time.sleep(delay)
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