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Exceptions: Difference between revisions
ignored nsresults
(ns_succeeded) |
(ignored nsresults) |
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the if statement would be deleted. | the if statement would be deleted. | ||
For these tasks, we need a full automatic rewriting system, with a pattern detection component and a patch generation component. The example patterns given here can be detected by looking at ASTs, so [[Dehydra GCC]] would be a great tool to use for detecting them. Once we have the list of patterns (say, as line numbers where the if statements start), we can work on an Elsa-based patch generator. | |||
= Removing NS_SUCCEEDED = | = Removing NS_SUCCEEDED = | ||
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This would be fairly easy to rewrite to the exceptions version, because the NS_FAILED check is easily identified as equivalent to letting the exception propagate to the caller. | This would be fairly easy to rewrite to the exceptions version, because the NS_FAILED check is easily identified as equivalent to letting the exception propagate to the caller. | ||
= Fixing Ignored nsresults = | |||
== Background == | |||
There are a fair number of call sites that ignore nsresult return values. This can be for several reasons, including: | |||
* The caller checks failure using some other condition (e.g., a null return value) | |||
* The function being called always returns NS_OK. | |||
* At this call site, the caller has ensured that the function will succeed. | |||
* The caller doesn't need to respond to errors. | |||
These calls need checking before we can enable exceptions. In general, it won't be possible to ensure that a function doesn't throw an exception, especially if we use exceptions for OOM. Thus, call sites that now ignore nsresults need to be looked at and made exception safe. | |||
== Finding Ignored nsresults == | |||
The key need here is a tool to automatically find call sites that ignore return values. There is a script under development (by dmandelin) that does this, but it needs to be improved to handle all the special cases, such as checking for a null return value. | |||
Once the list is in place, the calls will need manual attention. | |||
= Old Material = | |||
== Benefits of Exceptions == | == Benefits of Exceptions == | ||