python_pinger.git

Add a version that uses a lock instead of a queue.
Parent 7019525
David Blume

David Blume commited on 2019-07-06 11:32:09
Showing 3 changed files, with 83 additions and 0 deletions.

README.md
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@@ -75,6 +75,24 @@ No more race conditions! The worker threads mind their own business.
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 The worker threads remain in memory.
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+## Long Lived Looping Locked Workers
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+
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+That was fun using only the synchronized queue class and no locks. But now that
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+we've got the long lived looping workers that don't need their own queue, let's
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+replace the print manager with a threading lock.
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+
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+![Long Lived Looping Locked Workers](http://dlma.com/images/python_pinger/ping_long_lived_looping_locked_workers.png)
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+
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+See the source: **[long\_lived\_looping\_locked\_workers.py](http://git.dlma.com/python_pinger.git/blob/master/long_lived_looping_locked_workers.py)**
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+
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+### Upsides
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+
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+Got rid of the entire printer thread.
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+
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+### Downsides
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+
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+Uses a lock, which in more complex applications with multiple locks becomes difficult to reason about.
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+
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 ## Is it any good?
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 [Yes](https://news.ycombinator.com/item?id=3067434).
images/ping_long_lived_looping_locked_workers.png
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long_lived_looping_locked_workers.py
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@@ -0,0 +1,65 @@
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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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+printer_lock = threading.Lock()
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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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+            log(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 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 printer_lock:
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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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+    log(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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+
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+    # Stay alive forever. Join the last worker thread.
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+    t.join()
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