Exceptions - Revision history

Dmandelin at 23:26, 31 January 2008

2008-01-31T23:26:55Z

← Older revision		Revision as of 23:26, 31 January 2008
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	* Rewrite call sites that use NS_SUCCEEDED		* Rewrite call sites that use NS_SUCCEEDED

	These steps are explained in more detail below. And by the way, we'd love to have community help with any of these.		These steps are explained in more detail below. And by the way, we'd love to have community help with any of these. Look for "Coding Task" below to find small but useful bites of work that you might be interested in starting on.

	= Improved OOM Handling =		= Improved OOM Handling =

Dmandelin: /* Old Material */

2008-01-31T23:25:33Z

Old Material

← Older revision		Revision as of 23:25, 31 January 2008
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	= ~~Old Material~~ =		= Far Future Stuff =

			This was the original plan for implementing exceptions, now categorized as far future. Also hopefully these steps will be easier once we've done the medium-term stuff documented above.

	== Benefits of Exceptions ==		== Benefits of Exceptions ==

Dmandelin: /* Finding Ignored nsresults */

2008-01-31T23:24:13Z

Finding Ignored nsresults

← Older revision		Revision as of 23:24, 31 January 2008
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	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.		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.

			Coding Task 5: Finish the ignored nsresult analysis.

	Once the list is in place, the calls will need manual attention.		Once the list is in place, the calls will need manual attention.

Dmandelin: /* Code Changes */

2008-01-31T23:23:31Z

Code Changes

← Older revision		Revision as of 23:23, 31 January 2008
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	== Code Changes ==		== Code Changes ==

	Coding Task X: Create an analysis to check for methods that modify outparams when the return a nonzero nsresult. Eventually this analysis should be a gcc plugin so it can be integrated with the build process.		Coding Task 3: Create an analysis to check for methods that modify outparams when the return a nonzero nsresult. Eventually this analysis should be a gcc plugin so it can be integrated with the build process.

	Coding Task Y: Create an analysis to find methods that always return non-null outparams when the nsresult is NS_OK. Eventually, we want to annotate these methods with gcc attributes and enforce the annotation with a gcc plugin.		Coding Task 4: Create an analysis to find methods that always return non-null outparams when the nsresult is NS_OK. Eventually, we want to annotate these methods with gcc attributes and enforce the annotation with a gcc plugin.

	= Fixing Ignored nsresults =		= Fixing Ignored nsresults =

Dmandelin: /* Contracts for Outparams */

2008-01-31T23:23:05Z

Contracts for Outparams

← Older revision		Revision as of 23:23, 31 January 2008
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	== Background ==		== Background ==

			Some methods ("getters") 'return' a value other than an nsresult to the caller. Generally, the value is returned through a pointer-typed parameter, a.k.a., outparam. As of Mozilla 1.9, it's not always clear whether the returned value can be null if there is not error, or if the value can be changed if there is an error, etc., making things more confusing for callers.

			This situation needs to be cleared up for exceptions. With exceptions, we want these methods to return their value directly, which will have performance and developer sanity benefits. In that case, when there is an exception, no value is returned at all to the calling context. Thus, for all methods, '''when the error code is nonzero, outparams should not be modified'''.

			Some methods have the property that when the return code is NS_OK, the outparam is non-null (equivalently, when the outparam is non-null, the return code is nonzero). We want to identify these methods, because for them, a check for null is a valid way of checking for an error, and should be treated the same as an nsresult check for the other refactorings discussed here.

			== Code Changes ==

			Coding Task X: Create an analysis to check for methods that modify outparams when the return a nonzero nsresult. Eventually this analysis should be a gcc plugin so it can be integrated with the build process.

			Coding Task Y: Create an analysis to find methods that always return non-null outparams when the nsresult is NS_OK. Eventually, we want to annotate these methods with gcc attributes and enforce the annotation with a gcc plugin.

	= Fixing Ignored nsresults =		= Fixing Ignored nsresults =

Dmandelin: added section for outparam contracts

2008-01-31T22:51:22Z

added section for outparam contracts

← Older revision		Revision as of 22:51, 31 January 2008
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	* Remove all current OOM handling code		* Remove all current OOM handling code

			* Create contracts for outparams

	* Rewrite call sites that ignore nsresults		* Rewrite call sites that ignore nsresults
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	Coding Task 2: Dehydra GCC script to detect explicit tests for NS_OUT_OF_MEMORY return value.		Coding Task 2: Dehydra GCC script to detect explicit tests for NS_OUT_OF_MEMORY return value.

			= Contracts for Outparams =

			== Background ==

	= Fixing Ignored nsresults =		= Fixing Ignored nsresults =

Dmandelin at 22:50, 31 January 2008

2008-01-31T22:50:07Z

@@ Line 6: / Line 6: @@
 * Remove all current OOM handling code
 * Rewrite call sites that use NS_SUCCEEDED
 These steps are explained in more detail below. And by the way, we'd love to have community help with any of these.
@@ Line 66: / Line 66: @@
 Coding Task 2: Dehydra GCC script to detect explicit tests for NS_OUT_OF_MEMORY return value.
 = Removing NS_SUCCEEDED =
@@ Line 97: / Line 120: @@
 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.
 = Old Material =

Dmandelin: coding tasks

2008-01-31T22:48:03Z

coding tasks

← Older revision		Revision as of 22:48, 31 January 2008
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	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.		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.

			Coding Task 1: Dehydra GCC script to detect null pointer checks for allocated memory.

			Coding Task 2: Dehydra GCC script to detect explicit tests for NS_OUT_OF_MEMORY return value.

	= Removing NS_SUCCEEDED =		= Removing NS_SUCCEEDED =

Dmandelin: ignored nsresults

2008-01-31T22:31:42Z

ignored nsresults

@@ Line 60: / Line 60: @@
 the if statement would be deleted.
 = Removing NS_SUCCEEDED =
@@ Line 90: / Line 92: @@
 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.
 == Benefits of Exceptions ==

Dmandelin: ns_succeeded

2008-01-31T22:19:06Z

ns_succeeded

@@ Line 6: / Line 6: @@
 * Remove all current OOM handling code
 * Rewrite call sites that ignore nsresults
 These steps are explained in more detail below. And by the way, we'd love to have community help with any of these.
@@ Line 60: / Line 60: @@
 the if statement would be deleted.
 == Benefits of Exceptions ==