Revision: 5784
Author: [email protected]
Date: Thu Jul 23 14:21:00 2009
Log: Edited wiki page through web user interface.
http://code.google.com/p/google-web-toolkit/source/detail?r=5784
Modified:
/wiki/WebModeExceptions.wiki
=======================================
--- /wiki/WebModeExceptions.wiki Fri Feb 27 07:32:06 2009
+++ /wiki/WebModeExceptions.wiki Thu Jul 23 14:21:00 2009
@@ -61,6 +61,16 @@
* `collect()` raises an exception and passes it to `infer()`.
* `infer()` is implemented and uses the browser's `e.stack` or
`e.message` property to read activation records to produce a reasonably
complete stack trace.
+= Emulated Stack Data =
+
+The GWT compiler can optionally emit JavaScript code to maintain a
meta-stack that emulates standard JS dispatch semantics. This meta-stack
can be used to provide stack trace data on browsers that do not provide
stack data for all exception types. This is implemented as an additional
compiler pass that is conditionalized on the presence of
`StackTraceCreator.CollectorEmulated` within the compilation. Full
documentation on the transforms performed is located in the javadoc for
[http://code.google.com/p/google-web-toolkit/source/browse/trunk/dev/core/src/com/google/gwt/dev/js/JsStackEmulator.java
JsStackEmulator], but the basic transformation is as follows:
+ * The execution stack is modeled as an array that contains references to
the JavaScript functions being executed. There is a global variable that
maintains the current stack depth and an optional co-array that provides
current file and line number data.
+ * A stack frame is pushed on every function entrance. This involves
incrementing the stack depth counter and assigning the current function
into the meta-stack array. The stack depth for the function's invocation
is saved in a local variable.
+ * Before every last statement in normal flow control, the stack is
popped simply by decrementing the stack depth variable. The last statement
is any return statement not in a try/finally block, conditionally the last
statement in a finally block whose associated try contains a return
statement, and the last statement in the function.
+ * A return statement inside of a try block with an associated finally
block simply sets a function-local variable indicating that the stack
should be popped at the end of the finally block.
+ * When any exception is thrown (Java-derived or a native browser
exception), the stack depth is reset after the call to `Exceptions.caught`
to the function's local stack index variable.
+ * In order to ensure that a native exception's stack data is recorded
properly and any subsequent finally block is executed with the correct
global stack depth, any try/finally statement without a catch block has a
trivial catch block added to ensure the currently-propagating exception has
been correctly wrapped, to reset the global stack depth to the local stack
index, and then to re-throw the exception.
+
= Resymbolization =
Method names in deployed code will have been obfuscated and will not be
particularly useful as encoded in the module permutations. To that end, a
means for resymbolizing a stack trace has been implemented.
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http://groups.google.com/group/Google-Web-Toolkit-Contributors
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