diff options
Diffstat (limited to 'lib/spack/llnl/util/lock.py')
| -rw-r--r-- | lib/spack/llnl/util/lock.py | 167 |
1 files changed, 84 insertions, 83 deletions
diff --git a/lib/spack/llnl/util/lock.py b/lib/spack/llnl/util/lock.py index 3cd02befe5..6e49bf74e6 100644 --- a/lib/spack/llnl/util/lock.py +++ b/lib/spack/llnl/util/lock.py @@ -1,5 +1,5 @@ ############################################################################## -# Copyright (c) 2013, Lawrence Livermore National Security, LLC. +# Copyright (c) 2013-2015, Lawrence Livermore National Security, LLC. # Produced at the Lawrence Livermore National Laboratory. # # This file is part of Spack. @@ -22,134 +22,135 @@ # along with this program; if not, write to the Free Software Foundation, # Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA ############################################################################## -"""Lock implementation for shared filesystems.""" import os import fcntl import errno import time import socket -# Default timeout for locks. -DEFAULT_TIMEOUT = 60 +# Default timeout in seconds, after which locks will raise exceptions. +_default_timeout = 60 -class _ReadLockContext(object): - """Context manager that takes and releases a read lock. +# Sleep time per iteration in spin loop (in seconds) +_sleep_time = 1e-5 - Arguments are lock and timeout (default 5 minutes) - """ - def __init__(self, lock, timeout=DEFAULT_TIMEOUT): - self._lock = lock - self._timeout = timeout - def __enter__(self): - self._lock.acquire_read(self._timeout) +class Lock(object): + def __init__(self,file_path): + self._file_path = file_path + self._fd = None + self._reads = 0 + self._writes = 0 - def __exit__(self,type,value,traceback): - self._lock.release_read() + def _lock(self, op, timeout): + """This takes a lock using POSIX locks (``fnctl.lockf``). -class _WriteLockContext(object): - """Context manager that takes and releases a write lock. + The lock is implemented as a spin lock using a nonblocking + call to lockf(). - Arguments are lock and timeout (default 5 minutes) - """ - def __init__(self, lock, timeout=DEFAULT_TIMEOUT): - self._lock = lock - self._timeout = timeout + 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. - def __enter__(self): - self._lock.acquire_write(self._timeout) + 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) - def __exit__(self,type,value,traceback): - self._lock.release_write() + 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.") -class Lock(object): - """Distributed file-based lock using ``flock``.""" - def __init__(self, file_path): - self._file_path = file_path - self._fd = os.open(file_path,os.O_RDWR) - self._reads = 0 - self._writes = 0 + 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. - def write_lock(self, timeout=DEFAULT_TIMEOUT): - """Convenience method that returns a write lock context.""" - return _WriteLockContext(self, timeout) + """ + fcntl.lockf(self._fd,fcntl.LOCK_UN) + os.close(self._fd) + self._fd = None - def read_lock(self, timeout=DEFAULT_TIMEOUT): - """Convenience method that returns a read lock context.""" - return _ReadLockContext(self, timeout) + 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. - def acquire_read(self, timeout): - """ - Implements recursive lock. If held in both read and write mode, - the write lock will be maintained until all locks are released """ if self._reads == 0 and self._writes == 0: self._lock(fcntl.LOCK_SH, timeout) self._reads += 1 - def acquire_write(self, timeout): - """ - Implements recursive lock + 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. """ if self._writes == 0: self._lock(fcntl.LOCK_EX, timeout) self._writes += 1 - def _lock(self, op, timeout): - """ - The timeout is implemented using nonblocking flock() - to avoid using signals for timing - Write locks store pid and host information to the lock file - Read locks do not store data - """ - total_time = 0 - while total_time < timeout: - try: - fcntl.flock(self._fd, op | fcntl.LOCK_NB) - if op == fcntl.LOCK_EX: - with open(self._file_path, 'w') as f: - f.write("pid = " + str(os.getpid()) + ", host = " + socket.getfqdn()) - return - except IOError as error: - if error.errno == errno.EAGAIN or error.errno == EACCES: - pass - else: - raise - time.sleep(0.1) - total_time += 0.1 + 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. - def release_read(self): - """ - Assert there is a lock of the right type to release, recursive lock """ assert self._reads > 0 - if self._reads == 1 and self._writes == 0: - self._unlock() + self._reads -= 1 + if self._reads == 0 and self._writes == 0: + self._unlock() + return True + return False def release_write(self): - """ - Assert there is a lock of the right type to release, recursive lock + """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() + self._writes -= 1 + if self._writes == 0 and self._reads == 0: + self._unlock() + return True + return False - def _unlock(self): - """ - Releases the lock regardless of mode. Note that read locks may be - masquerading as write locks at times, but this removes either. - """ - fcntl.flock(self._fd, fcntl.LOCK_UN) +class LockError(Exception): + """Raised when an attempt to acquire a lock times out.""" + pass |