title: ValueError: semaphore or lock released too many times?
body: <p>I get <code>ValueError: semaphore or lock released too many times</code> when I try to do <code>pip install matplotlib</code> in Cygwin. What do I do?</p>
  
  <p>UPDATE:</p>
  
  <pre><code>$ pip install matplotlib
  Downloading/unpacking matplotlib
    You are installing an externally hosted file. Future versions of pip will default to disallowing externally hosted files.
    You are installing a potentially insecure and unverifiable file. Future versions of pip will default to disallowing insecure files.
    Downloading matplotlib-1.3.0.tar.gz (42.1MB): 42.1MB downloaded
    Running setup.py egg_info for package matplotlib
      ============================================================================
      Edit setup.cfg to change the build options
  
      BUILDING MATPLOTLIB
                  matplotlib: yes [1.3.0]
                      python: yes [2.7.5 (default, Jul 30 2013, 14:34:22)  [GCC
                              4.8.1]]
                    platform: yes [cygwin]
  
      REQUIRED DEPENDENCIES AND EXTENSIONS
                       numpy: yes [version 1.7.1]
                    dateutil: yes [using dateutil version 2.1]
                     tornado: yes [tornado was not found. It is required for the
                              WebAgg backend. pip/easy_install may attempt to
                              install it after matplotlib.]
                   pyparsing: yes [pyparsing was not found. It is required for
                              mathtext support. pip/easy_install may attempt to
                              install it after matplotlib.]
                       pycxx: yes [Couldn't import.  Using local copy.]
                      libagg: yes [pkg-config information for 'libagg' could not
                              be found. Using local copy.]
                    freetype: yes [version 16.1.10]
                         png: yes [version 1.5.14]
  
      OPTIONAL SUBPACKAGES
                 sample_data: yes [installing]
                    toolkits: yes [installing]
                       tests: yes [nose 0.11.1 or later is required to run the
                              matplotlib test suite]
  
      OPTIONAL BACKEND EXTENSIONS
                      macosx: no  [Mac OS-X only]
                      qt4agg: no  [PyQt4 not found]
      Process PoolWorker-1:
      Traceback (most recent call last):
        File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
          self.run()
        File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
          self._target(*self._args, **self._kwargs)
        File "/usr/lib/python2.7/multiprocessing/pool.py", line 102, in worker
          task = get()
        File "/usr/lib/python2.7/multiprocessing/queues.py", line 378, in get
          rrelease()
      ValueError: semaphore or lock released too many times
  </code></pre>