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scmutil: support background file closing
Closing files that have been appended to is relatively slow on
Windows/NTFS. This makes several Mercurial operations slower on
Windows.
The workaround to this issue is conceptually simple: use multiple
threads for I/O. Unfortunately, Python doesn't scale well to multiple
threads because of the GIL. And, refactoring our code to use threads
everywhere would be a huge undertaking. So, we decide to tackle this
problem by starting small: establishing a thread pool for closing
files.
This patch establishes a mechanism for closing file handles on separate
threads. The coordinator object is basically a queue of file handles to
operate on and a thread pool consuming from the queue.
When files are opened through the VFS layer, the caller can specify
that delay closing is allowed.
A proxy class for file handles has been added. We must use a proxy
because it isn't possible to modify __class__ on built-in types. This
adds some overhead. But as future patches will show, this overhead
is cancelled out by the benefit of closing file handles on background
threads.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Thu, 14 Jan 2016 13:34:59 -0800 |
parents | 4b0fc75f9403 |
children | 47ef023d0165 |
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#!/usr/bin/env python # # An example hgweb CGI script, edit as necessary # See also https://mercurial-scm.org/wiki/PublishingRepositories # Path to repo or hgweb config to serve (see 'hg help hgweb') config = "/path/to/repo/or/config" # Uncomment and adjust if Mercurial is not installed system-wide # (consult "installed modules" path from 'hg debuginstall'): #import sys; sys.path.insert(0, "/path/to/python/lib") # Uncomment to send python tracebacks to the browser if an error occurs: #import cgitb; cgitb.enable() from mercurial import demandimport; demandimport.enable() from mercurial.hgweb import hgweb, wsgicgi application = hgweb(config) wsgicgi.launch(application)