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locks: add configuration and command-line options to enable/disable locks (#7692)

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- spack.util.lock behaves the same as llnl.util.lock, but Lock._lock and
  Lock._unlock do nothing.

- can be disabled with a control variable.

- configuration options can enable/disable locking:
  - `locks` option in spack configuration controls whether Spack will use filesystem locks or not.
  - `-l` and `-L` command-line options can force-disable or force-enable locking.

- Spack will check for group- and world-writability before disabling
  locks, and it will not allow a group- or world-writable instance to
  have locks disabled.

- update documentation
This commit is contained in:
Todd Gamblin
2018-05-18 14:41:03 -07:00
committed by GitHub
parent 780cc9d72d
commit 54201e3c02
11 changed files with 323 additions and 54 deletions
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30
lib/spack/llnl/util/lock.py
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@@ -195,11 +195,13 @@ def acquire_read(self, timeout=_default_timeout):
"""
if self._reads == 0 and self._writes == 0:
tty.debug('READ LOCK: {0.path}[{0._start}:{0._length}] [Acquiring]'
.format(self))
self._debug(
'READ LOCK: {0.path}[{0._start}:{0._length}] [Acquiring]'
.format(self))
self._lock(fcntl.LOCK_SH, timeout=timeout) # can raise LockError.
tty.debug('READ LOCK: {0.path}[{0._start}:{0._length}] [Acquired]'
.format(self))
self._debug(
'READ LOCK: {0.path}[{0._start}:{0._length}] [Acquired]'
.format(self))
self._reads += 1
return True
else:
@@ -218,12 +220,13 @@ def acquire_write(self, timeout=_default_timeout):
"""
if self._writes == 0:
tty.debug(
self._debug(
'WRITE LOCK: {0.path}[{0._start}:{0._length}] [Acquiring]'
.format(self))
self._lock(fcntl.LOCK_EX, timeout=timeout) # can raise LockError.
tty.debug('WRITE LOCK: {0.path}[{0._start}:{0._length}] [Acquired]'
.format(self))
self._debug(
'WRITE LOCK: {0.path}[{0._start}:{0._length}] [Acquired]'
.format(self))
self._writes += 1
return True
else:
@@ -243,8 +246,9 @@ def release_read(self):
assert self._reads > 0
if self._reads == 1 and self._writes == 0:
tty.debug('READ LOCK: {0.path}[{0._start}:{0._length}] [Released]'
.format(self))
self._debug(
'READ LOCK: {0.path}[{0._start}:{0._length}] [Released]'
.format(self))
self._unlock() # can raise LockError.
self._reads -= 1
return True
@@ -265,8 +269,9 @@ def release_write(self):
assert self._writes > 0
if self._writes == 1 and self._reads == 0:
tty.debug('WRITE LOCK: {0.path}[{0._start}:{0._length}] [Released]'
.format(self))
self._debug(
'WRITE LOCK: {0.path}[{0._start}:{0._length}] [Released]'
.format(self))
self._unlock() # can raise LockError.
self._writes -= 1
return True
@@ -274,6 +279,9 @@ def release_write(self):
self._writes -= 1
return False
def _debug(self, *args):
tty.debug(*args)
class LockTransaction(object):
"""Simple nested transaction context manager that uses a file lock.