Author Sebastian.Noack
Recipients Sebastian.Noack, asvetlov, jyasskin, kristjan.jonsson, mklauber, pitrou, sbt
Date 2012-10-01.07:30:19
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Message-id <1349076620.66.0.0257730413729.issue8800@psf.upfronthosting.co.za>
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Yes, you could also look at the shared/exclusive lock as one lock with different states. But this approach is neither more common, have a look at Java's ReadWriteLock [1] for example, which works just like my patch does, except that a factory is returned instead of a tuple. Nor does it provide any of the benefits, I have mentioned before (same API as Lock and RLock, better compatibility with existing code an with statement, ability to pass the shared or exclusive lock separetly around). But maybe we could satisfy anybody, by following Richard's and Antoine's suggestion of returning a named tuple. So you could use the ShrdExclLock both ways:

# use a single object
lock = ShrdExclLock()

with lock.shared:
  ...

with lock.exclusive:
  ...

# unpack the the object into two variables and pass them separately around
shrd_lock, excl_lock = ShrdExclLock()

Thread(target=reader, args=(shrd_lock,)).start()
Thread(target=writer, args=(excl_lock,)).start)


The majority of us seems to prefer the terms shared and exclusive. However I can't deny that the terms read and write are more common, even though there are also notable exmples where the terms shared and exclusive are used [2] [3]. But let us ignore how other call it for now, and get to the origin of both set of terms, in order to figure out which fits best into Python:

shared/exclusive -> abstract description of what it is
read/write       -> best known use case

The reason why I prefer the terms shared and exculsive, is that it is more distinct and less likely to get misunderstand. Also naming a generic implementation after a specific use case is bad API design and I don't know any other case where that was done, in the Python core library.


[1] http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/locks/ReadWriteLock.html
[2] http://www.postgresql.org/docs/9.2/static/explicit-locking.html
[3] http://www.unix.com/man-page/freebsd/9/SX/
History
Date User Action Args
2012-10-01 07:30:21Sebastian.Noacksetrecipients: + Sebastian.Noack, pitrou, kristjan.jonsson, jyasskin, asvetlov, sbt, mklauber
2012-10-01 07:30:20Sebastian.Noacksetmessageid: <1349076620.66.0.0257730413729.issue8800@psf.upfronthosting.co.za>
2012-10-01 07:30:20Sebastian.Noacklinkissue8800 messages
2012-10-01 07:30:19Sebastian.Noackcreate