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The cycle collector heap dump is useful for figuring out why the cycle collector is keeping an object alive. These can either be manually or automatically generated. | The cycle collector heap dump is useful for figuring out why the cycle collector is keeping an object alive. These can either be manually or automatically generated. | ||
To manually generate a CC dump, in | To manually generate a CC dump, even in a non-debug build, enable the Error Console, by going to about:config and setting devtools.errorconsole.enabled to true. Then open a new window, go to Tools, Web Developer, Web Console. | ||
Then evaluate this expression: | Then evaluate this expression: | ||
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.createInstance(Components.interfaces.nsICycleCollectorListener)) | .createInstance(Components.interfaces.nsICycleCollectorListener)) | ||
By default, the cycle collector will only log the objects it normally looks at. Sometimes it can be useful to disable the optimizations the cycle collector does in order to get more detailed information. In this case, the method allTraces() can be used: | |||
window.QueryInterface(Components.interfaces.nsIInterfaceRequestor). | window.QueryInterface(Components.interfaces.nsIInterfaceRequestor). | ||
getInterface(Components.interfaces.nsIDOMWindowUtils). | getInterface(Components.interfaces.nsIDOMWindowUtils). | ||
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.createInstance(Components.interfaces.nsICycleCollectorListener).allTraces()) | .createInstance(Components.interfaces.nsICycleCollectorListener).allTraces()) | ||
This creates a file named cc-edges-NNNN.log and writes a dump of the heap known to the cycle collector, which includes JS objects and also native C++ objects that participate in cycle collection, to the file. | This creates a file named cc-edges-NNNN.log and writes a dump of the heap known to the cycle collector, which includes JS objects and also native C++ objects that participate in cycle collection, to the file. It will also log the contents of the Javascript heap to a file named gc-edges-NNNN.log. | ||
Since Firefox 18 (night builds after 2012-09-13) one can override the default location of the log files by setting the MOZ_CC_LOG_DIRECTORY environment variable. http://people.mozilla.com/~mleibovic/cc-dump.xpi is an addon for Android Firefox which uses that to save files to /sdcard. The code for this addon is available on [https://github.com/leibovic/skeleton-addon-fxandroid/tree/cc Github]. | Since Firefox 18 (night builds after 2012-09-13) one can override the default location of the log files by setting the MOZ_CC_LOG_DIRECTORY environment variable. http://people.mozilla.com/~mleibovic/cc-dump.xpi is an addon for Android Firefox which uses that to save files to /sdcard. The code for this addon is available on [https://github.com/leibovic/skeleton-addon-fxandroid/tree/cc Github]. | ||
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* Older builds created the file in Firefox's current working directory (usually the current working directory where Firefox was started). That meant that on Windows 7 and Vista, you typically had to run Firefox as Administrator to create the file. | * Older builds created the file in Firefox's current working directory (usually the current working directory where Firefox was started). That meant that on Windows 7 and Vista, you typically had to run Firefox as Administrator to create the file. | ||
To | To log every cycle collection, set the XPCOM_CC_LOG_ALL environment variable. To log only shutdown collections, set XPCOM_CC_LOG_SHUTDOWN. To make any shutdown CCs AllTraces() at shutdown, set XPCOM_CC_ALL_TRACES_AT_SHUTDOWN. The latter two are useful for debugging shutdown leaks. | ||
To analyze a cycle collector dump, you need the scripts from [https://github.com/amccreight/heapgraph/tree/master/cc Github]. The relevant scripts are find_roots.py and parse_cc_graph.py (which is called by find_roots). Calling find_roots on a CC file with a specific object or kind of object will produce paths from rooting objects to the specified objects. Most big leaks include an nsGlobalWindow, so that's a good class to try if you don't have any better idea. | To analyze a cycle collector dump, you need the scripts from [https://github.com/amccreight/heapgraph/tree/master/cc Github]. The relevant scripts are find_roots.py and parse_cc_graph.py (which is called by find_roots). Calling find_roots on a CC file with a specific object or kind of object will produce paths from rooting objects to the specified objects. Most big leaks include an nsGlobalWindow, so that's a good class to try if you don't have any better idea. | ||
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* Simple, ugly, yet rather powerful [https://bugzilla.mozilla.org/show_bug.cgi?id=726346 about:cc] | * Simple, ugly, yet rather powerful [https://bugzilla.mozilla.org/show_bug.cgi?id=726346 about:cc] | ||
* Prettier but a bit slower [https://addons.mozilla.org/en-US/firefox/addon/cycle-collector-analyzer/?src=ss about:ccdump] | * Prettier but a bit slower [https://addons.mozilla.org/en-US/firefox/addon/cycle-collector-analyzer/?src=ss about:ccdump] | ||
=== Leak tools for medium-size object graphs === | === Leak tools for medium-size object graphs === | ||