On Sat, Oct 10, 2009 at 11:08 AM, jon <trambl...@mac.com> wrote:
> Hi Bill, in this theme of normal behavior, maybe this would make what i'm
> asking more clear.
>
> in an exercise of thought, if you wrote an app, and the only thing it did
> was put up a window permanently (for the run of it's process life), with a
> single webview in it, and hardwired a load of any particular website you
> wished that had any substance to load in that webview... and then put in a
> trigger to simply reload that same website every 20 seconds... and that
> was it, no number crunching, or extra processes, or UI.
>
> if you had to guess, if you looked in activity monitor, do you think
> this thought experiment would use disk IO every 20 seconds?
I built a simple application with a single window, a WebView, a text field
for URL, and a button to trigger a reload... all defined in the main xib. No
other code written. I turned off support for plugins, java and javascript
for the fun of it. Then I monitored that application and found the following
every time I loaded a page.
MacPro:~ shawnce$ sudo fs_usage -w -f filesys 26906 | tee fstrace.txt
11:24:03.163 open F=7 (R_____)
/Users/shawnce/Library/Cookies/Cookies.plist
0.000071 MyBasicWebView
11:24:03.163 fstat F=7
0.000005
MyBasicWebView
11:24:03.165 read F=7 B=0xe55d1
0.000544
MyBasicWebView
11:24:03.165 close F=7
0.000016
MyBasicWebView
11:24:03.272 ioctl F=7 <CMD=0x8004667e>
0.000003
MyBasicWebView
11:24:03.272 ioctl F=10 <CMD=0xc0206911>
0.000004
MyBasicWebView
11:24:03.272 fcntl F=7 <GETFL>
0.000003
MyBasicWebView
11:24:03.322 ioctl F=10 <CMD=0xc0206911>
0.000005
MyBasicWebView
11:24:03.322 ioctl F=10 <CMD=0xc0206911>
0.000002
MyBasicWebView
11:24:03.322 ioctl F=10 <CMD=0xc0206911>
0.000002
MyBasicWebView
11:24:03.322 ioctl F=10 <CMD=0xc0206911>
0.000002
MyBasicWebView
11:24:03.322 ioctl F=10 <CMD=0xc0206911>
0.000002
MyBasicWebView
11:24:03.645 fcntl F=3 <SETLK>
0.000007
MyBasicWebView
11:24:03.645 fcntl F=3 <SETLK>
0.000002
MyBasicWebView
11:24:03.645 fcntl F=3 <SETLK>
0.000003
MyBasicWebView
11:24:03.645 access [ 2] (___F)
/Users/shawnce/Library/Caches/com.yourcompany.MyBasicWebView/Cache.db-journal
0.000082 MyBasicWebView
....long list of stuff snipped...
If I watch this application using the File Activity template of Instruments
I get a lot of nice information. For example I can see the stack track
related to a disk write among many other things.
13 CFNetwork CFURLCacheWorkerThread(void*)
12 CoreFoundation CFRunLoopRunInMode
11 CoreFoundation CFRunLoopRunSpecific
10 CFNetwork CFURLCacheTimerCallback(__CFRunLoopTimer*, void*)
9 CFNetwork ProcessCacheTasks(__CFURLCache*)
8 CFNetwork __CFURLCache::ExecuteSQLInsert(_CFCachedURLResponse const*,
__CFString const*, _CFURLRequest const*)
7 CFNetwork __CFURLCache::StepSQLStatementToCompletion(sqlite3_stmt*,
long)
6 libsqlite3.0.dylib sqlite3_step
5 libsqlite3.0.dylib sqlite3Step
4 libsqlite3.0.dylib sqlite3VdbeExec
3 libsqlite3.0.dylib sqlite3BtreeInsert
2 libsqlite3.0.dylib sqlite3PagerWrite
1 libsqlite3.0.dylib pager_write
0 libSystem.B.dylib pwrite$UNIX2003
Which is exactly what I expected (and others) given the fact that by default
the URL loading sub-system used on Mac OS X will attempt to cache remote
resources. This is all done in support of the standard HTTP resource caching
scheme.
For example review...
<
http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/URLLoadingSystem/Concepts/CachePolicies.html#//apple_ref/doc/uid/20001843-BAJEAIEE
>
<
http://developer.apple.com/mac/library/documentation/Cocoa/Reference/WebKit/Classes/WebPreferences_Class/Reference/Reference.html#//apple_ref/occ/instm/WebPreferences/setCacheModel
:>
-Shawn
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