[Patches] [ python-Patches-1744382 ] Read Write lock

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Patches item #1744382, was opened at 2007-06-27 20:08
Message generated for change (Comment added) made by loewis
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Category: Modules
Group: Python 2.6
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Yaakov Nemoy (loupgaroublond)
Assigned to: Nobody/Anonymous (nobody)
Summary: Read Write lock

Initial Comment:
This is a Lock for handling both multiple readers and a single or multiple writers.  It allows any number of readers to acquire a 'lock' via a modified semaphore.  It also allows any number of writers to try to acquire a lock, which signals the lock to block new readers from acquiring, until the writers have had a chance to do their business.  Through a simple lock, multiple writers can wait in line, although only one writer can actually write at a time.

It also lets the developer use the 'with' statement, via  methods that return contextmanagers.

I actually had a couple of unimplemented ideas.

A) Writers can specify a deadline (or even use a default) such that after the deadline passes, the lock can use a callback to rollback/kill/pause readers, so that the writer doesn't wait an eternity.

B) Allowing the semaphore to have an upper limit of allowed readers (or anythings), Since I don't need it, i never programmed it, but it should be fairly trivial to implement if there is any demand.

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>Comment By: Martin v. Löwis (loewis)
Date: 2007-06-30 19:38

Message:
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The patch is unacceptable in its current form:
- it should be provided as a patch to threading.py, not as a separate
module
- it should have a name that follows "the convention", which seems to be
that 
  it should have "reader" and "writer" in its name (or "rw"). See how C#
and
  Java do it (and other libraries you can find that provide such a
mechanism)
- it needs documentation
- it needs tests.

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