1 files changed, 175 insertions, 0 deletions
diff --git a/lib/spack/llnl/util/lock.py b/lib/spack/llnl/util/lock.py
new file mode 100644
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+++ b/lib/spack/llnl/util/lock.py
@@ -0,0 +1,175 @@
+##############################################################################
+# Copyright (c) 2013-2015, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Written by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://scalability-llnl.github.io/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License (as published by
+# the Free Software Foundation) version 2.1 dated February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+import os
+import fcntl
+import errno
+import time
+import socket
+
+# Default timeout in seconds, after which locks will raise exceptions.
+_default_timeout = 60
+
+# Sleep time per iteration in spin loop (in seconds)
+_sleep_time = 1e-5
+
+
+class Lock(object):
+    def __init__(self,file_path):
+        self._file_path = file_path
+        self._fd = None
+        self._reads = 0
+        self._writes = 0
+
+
+    def _lock(self, op, timeout):
+        """This takes a lock using POSIX locks (``fnctl.lockf``).
+
+        The lock is implemented as a spin lock using a nonblocking
+        call to lockf().
+
+        On acquiring an exclusive lock, the lock writes this process's
+        pid and host to the lock file, in case the holding process
+        needs to be killed later.
+
+        If the lock times out, it raises a ``LockError``.
+        """
+        start_time = time.time()
+        while (time.time() - start_time) < timeout:
+            try:
+                if self._fd is None:
+                    self._fd = os.open(self._file_path, os.O_RDWR)
+
+                fcntl.lockf(self._fd, op | fcntl.LOCK_NB)
+                if op == fcntl.LOCK_EX:
+                    os.write(self._fd, "pid=%s,host=%s" % (os.getpid(), socket.getfqdn()))
+                return
+
+            except IOError as error:
+                if error.errno == errno.EAGAIN or error.errno == errno.EACCES:
+                    pass
+                else:
+                    raise
+            time.sleep(_sleep_time)
+
+        raise LockError("Timed out waiting for lock.")
+
+
+    def _unlock(self):
+        """Releases a lock using POSIX locks (``fcntl.lockf``)
+
+        Releases the lock regardless of mode. Note that read locks may
+        be masquerading as write locks, but this removes either.
+
+        """
+        fcntl.lockf(self._fd,fcntl.LOCK_UN)
+        os.close(self._fd)
+        self._fd = None
+
+
+    def acquire_read(self, timeout=_default_timeout):
+        """Acquires a recursive, shared lock for reading.
+
+        Read and write locks can be acquired and released in arbitrary
+        order, but the POSIX lock is held until all local read and
+        write locks are released.
+
+        Returns True if it is the first acquire and actually acquires
+        the POSIX lock, False if it is a nested transaction.
+
+        """
+        if self._reads == 0 and self._writes == 0:
+            self._lock(fcntl.LOCK_SH, timeout)   # can raise LockError.
+            self._reads += 1
+            return True
+        else:
+            self._reads += 1
+            return False
+
+
+    def acquire_write(self, timeout=_default_timeout):
+        """Acquires a recursive, exclusive lock for writing.
+
+        Read and write locks can be acquired and released in arbitrary
+        order, but the POSIX lock is held until all local read and
+        write locks are released.
+
+        Returns True if it is the first acquire and actually acquires
+        the POSIX lock, False if it is a nested transaction.
+
+        """
+        if self._writes == 0:
+            self._lock(fcntl.LOCK_EX, timeout)   # can raise LockError.
+            self._writes += 1
+            return True
+        else:
+            self._writes += 1
+            return False
+
+
+    def release_read(self):
+        """Releases a read lock.
+
+        Returns True if the last recursive lock was released, False if
+        there are still outstanding locks.
+
+        Does limited correctness checking: if a read lock is released
+        when none are held, this will raise an assertion error.
+
+        """
+        assert self._reads > 0
+
+        if self._reads == 1 and self._writes == 0:
+            self._unlock()      # can raise LockError.
+            self._reads -= 1
+            return True
+        else:
+            self._reads -= 1
+            return False
+
+
+    def release_write(self):
+        """Releases a write lock.
+
+        Returns True if the last recursive lock was released, False if
+        there are still outstanding locks.
+
+        Does limited correctness checking: if a read lock is released
+        when none are held, this will raise an assertion error.
+
+        """
+        assert self._writes > 0
+
+        if self._writes == 1 and self._reads == 0:
+            self._unlock()      # can raise LockError.
+            self._writes -= 1
+            return True
+        else:
+            self._writes -= 1
+            return False
+
+
+class LockError(Exception):
+    """Raised when an attempt to acquire a lock times out."""
+    pass