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Re: Getting a SIGALERT - but not sure what thread it's in.
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Re: Getting a SIGALERT - but not sure what thread it's in.


  • Subject: Re: Getting a SIGALERT - but not sure what thread it's in.
  • From: Daniel Jalkut <email@hidden>
  • Date: Tue, 24 Jan 2006 08:55:38 -0500

Hi John. Usually Xcode will show you the stack that crashed, so unless you have reason to be especially skeptical, I would look carefully at the top of the stack where it interrupts.

If you're paranoid and not sure that it's actually the crashing thread, you could try displaying all thread backtraces, from the console:

1. Select "Console Log" from the Debug menu.
2. Type "t a a bt" - this is GDB shorthand for "thread all apply backtrace" - or something :)
3. You should see a confirmation before the crashing thread. Something like "Thread 3 Crashed:"


As to your understanding of what the EXEC_BAD_ACCESS means - yes it probably means you're reading from "bad memory." If you're stumped and can't see any relationship between the crashing code and your code, you might try turning on "Guard Malloc." It makes your app run as slow as molasses but often detects memory impropriety at the source of the problem. Just select "Enable Guard Malloc" from the bottom of the Debug menu before debugging your app. And remember to turn it off later or you'll think Xcode is really, really, slow at debugging :)

Daniel

On Jan 24, 2006, at 12:58 AM, John Draper wrote:

Hi,

I have 3 threads running. I'm to assume my main application is thread-1
when shown in the debug window.


When running my App, I'm getting an EXEC_BAD_ACCESS. In my
X-Code, the thread-3 is selected. Is this the thread where I got
this error? Or could it be in another thread. and the source debugger
just happened to have thread-3 selected. Or putting it another way...
when the program encounters this EXEC_BAD_ACCESS error
condition, does the source level debugger then switch to the thread
that generated this error? I'm assuming I'm just trying to access
memory outside my heap space, is this true? Or is something else
going wrong and I'm just knocking on the wrong door?


John


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References: 
 >Getting a SIGALERT - but not sure what thread it's in. (From: John Draper <email@hidden>)

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