Ensure only on instance of dosage is running to prevent accedental DoS on sites with multiple comics.

doc/changelog.txt

@@ -1,3 +1,10 @@
+Dosage 2.10 (released xx.xx.2014)
+
+Changes:
+- cmdline: Ensure only one instance of dosage is running to prevent
+  accidental DoS when fetching multiple comics of one site.
+
+
 Dosage 2.9 (released 22.12.2013)
 
 Features:

doc/dosage.1

@@ -148,11 +148,6 @@ the beginning.
 .B dosage \-a calvinandhobbes:2012/07/22
 .RE
 .PP
-On Unix, \fBxargs(1)\fP can download several comic strips in parallel,
-for example using up to 4 processes:
-.RS
-.B cd Comics && find . -type d | xargs -n1 -P4 dosage -b . -v
-.RE
 .SH ENVIRONMENT
 .IP HTTP_PROXY
 .B dosage

doc/dosage.1.html

@@ -202,13 +202,6 @@ the beginning.
 
 <P>
 
-On Unix, <B>xargs(1)</B> can download several comic strips in parallel,
-for example using up to 4 processes:
-<DL COMPACT><DT><DD>
-<B>cd Comics &amp;&amp; find . -type d | xargs -n1 -P4 dosage -b . -v</B>
-
-</DL>
-
 <A NAME="lbAI">&nbsp;</A>
 <H2>ENVIRONMENT</H2>
 

doc/dosage.1.html.diff

@@ -9,15 +9,6 @@
  
  <A NAME="lbAB">&nbsp;</A>
  <H2>NAME</H2>
-@@ -190,7 +190,7 @@
- 
- <P>
- 
--On Unix, <B><A HREF="../man1/xargs.1.html">xargs</A>(1)</B> can download several comic strips in parallel,
-+On Unix, <B>xargs(1)</B> can download several comic strips in parallel,
- for example using up to 4 processes:
- <DL COMPACT><DT><DD>
- <B>cd Comics &amp;&amp; find . -type d | xargs -n1 -P4 dosage -b . -v</B>
 @@ -282,7 +282,7 @@
  </DL>
  <HR>

doc/dosage.txt

@@ -131,11 +131,6 @@ EXAMPLES
        backwards to the beginning.
               dosage -a calvinandhobbes:2012/07/22
 
-       On  Unix,  xargs(1) can download several comic strips in paral‐
-       lel, for example using up to 4 processes:
-              cd Comics && find . -type d | xargs -n1 -P4 dosage -b  .
-              -v
-
 ENVIRONMENT
        HTTP_PROXY
               dosage  will use the specified HTTP proxy when download‐

dosage

@@ -16,7 +16,7 @@ import argparse
 import pydoc
 from io import StringIO
 
-from dosagelib import events, scraper, configuration
+from dosagelib import events, scraper, configuration, singleton
 from dosagelib.output import out
 from dosagelib.util import internal_error, getDirname, strlimit, getLangName
 from dosagelib.ansicolor import get_columns
@@ -271,6 +271,8 @@ def getStrips(scraperobj, options):
 def run(options):
     """Execute comic commands."""
     setOutputInfo(options)
+    # ensure only one instance of dosage is running
+    me = singleton.SingleInstance()
     if options.version:
         return displayVersion(options.verbose)
     if options.list:

dosagelib/singleton.py

@@ -0,0 +1,86 @@
+# -*- coding: iso-8859-1 -*-
+# Copied from: https://github.com/pycontribs/tendo
+# License: PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
+# Author: Sorin Sbarnea
+# Changes: changed logging and formatting
+
+import sys
+import os
+import errno
+import tempfile
+from .output import out
+
+
+class SingleInstance(object):
+    """
+    To prevent a script from running in parallel instantiate the
+    SingleInstance() class. If is there another instance
+    already running it will exit the application with the message
+    "Another instance is already running, quitting.",
+    returning an error code of -1.
+
+    >>> me = SingleInstance()
+
+    This is very useful to execute scripts by crontab that should only run
+    one at a time.
+
+    Note that this works by creating a lock file with a filename based
+    on the full path to the script file.
+    """
+
+    def __init__(self, flavor_id="", exit_code=-1):
+        """Create an exclusive lockfile or exit with an error and the given
+        exit code."""
+        self.initialized = False
+        scriptname = os.path.splitext(os.path.abspath(sys.argv[0]))[0]
+        lockname = scriptname.replace("/", "-").replace(":", "").replace("\\", "-")
+        if flavor_id:
+            lockname += "-%s" % flavor_id
+        lockname += '.lock'
+        tempdir = tempfile.gettempdir()
+        self.lockfile = os.path.normpath(os.path.join(tempdir, lockname))
+        out.debug("SingleInstance lockfile: " + self.lockfile)
+        print(self.lockfile)
+        if sys.platform == 'win32':
+            try:
+                # file already exists, try to remove it in case the previous
+                # execution was interrupted
+                if os.path.exists(self.lockfile):
+                    os.unlink(self.lockfile)
+                self.fd = os.open(self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
+            except OSError:
+                type, e, tb = sys.exc_info()
+                if e.errno == errno.EACCES: # EACCES == 13
+                    self.exit(exit_code)
+                raise
+        else:  # non Windows
+            import fcntl
+            self.fp = open(self.lockfile, 'w')
+            try:
+                fcntl.lockf(self.fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
+                # raises IOError on Python << 3.3, else OSError
+            except (IOError, OSError):
+                self.exit(exit_code)
+        self.initialized = True
+
+    def exit(self, exit_code):
+        """Exit with an error message and the given exit code."""
+        out.error("Another instance is already running, quitting.")
+        sys.exit(exit_code)
+
+    def __del__(self):
+        """Remove the lock file."""
+        if not self.initialized:
+            return
+        try:
+            if sys.platform == 'win32':
+                if hasattr(self, 'fd'):
+                    os.close(self.fd)
+                    os.unlink(self.lockfile)
+            else:
+                import fcntl
+                fcntl.lockf(self.fp, fcntl.LOCK_UN)
+                if os.path.isfile(self.lockfile):
+                    os.unlink(self.lockfile)
+        except StandardError as e:
+            out.exception("could not remove lockfile: %s" % e)

tests/test_singletoninstance.py

@@ -0,0 +1,45 @@
+# -*- coding: iso-8859-1 -*-
+# Copied from: https://github.com/pycontribs/tendo
+# License: PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
+# Author: Sorin Sbarnea
+# Changes: changed logging and formatting
+from unittest import TestCase
+from dosagelib import singleton
+from multiprocessing import Process
+
+
+def f(flavor_id):
+    return singleton.SingleInstance(flavor_id=flavor_id, exit_code=1)
+
+
+class TestSingleton(TestCase):
+
+    def test_1(self):
+        # test in current process
+        me = singleton.SingleInstance(flavor_id="test-1")
+        del me  # now the lock should be removed
+        self.assertTrue(True)
+
+    def test_2(self):
+        # test in current subprocess
+        p = Process(target=f, args=("test-2",))
+        p.start()
+        p.join()
+        # the called function should succeed
+        self.assertEqual(p.exitcode, 0)
+
+    def test_3(self):
+        # test in current process and subprocess with failure
+        # start first instance
+        me = f("test-3")
+        # second instance
+        p = Process(target=f, args=("test-3",))
+        p.start()
+        p.join()
+        self.assertEqual(p.exitcode, 1)
+        # third instance
+        p = Process(target=f, args=("test-3",))
+        p.start()
+        p.join()
+        self.assertEqual(p.exitcode, 1)
+        del me  # now the lock should be removed