I'm using Xcode 4.3.2 with lldb as my debugger.
I have inherited a project that contains code that is calling UIKit from secondary threads, as shown by these log messages:
2012-05-02 21:48:14.603 Appname Dev[77594:16e0f] void
_WebThreadLockFromAnyThread(bool), 0x8d5f810: Obtaining the web lock from a thread other than the main thread or the web thread. UIKit
should not be called from a secondary thread.
I have cleaned up most of the code that was making UIKit calls from secondary threads, but I am still occasionally seeing this message in the logs. The app is not crashing, so it's difficult to pinpoint where the problem lies.
I'd like to set a breakpoint on _WebThreadLockFromAnyThread, but when I try to set a symbolic breakpoint using:
b _WebThreadLockFromAnyThread
the debugger tells me:
breakpoint set --name '_WebThreadLockFromAnyThread' Breakpoint
created: 12: name = '_WebThreadLockFromAnyThread', locations = 0
(pending) WARNING: Unable to resolve breakpoint to any actual
locations.
I've also tried creating the symbolic breakpoint using the UI in the breakpoint navigator, but I'm not sure what to enter for the module. When I leave the module blank, the breakpoint is created but it's still not breaking when the log message appears in the debug console.
Can anyone tell me how I can go about adding a breakpoint on _WebThreadLockFromAnyThread, and also how I would determine what the defining module is for this symbol?
Just leave out the underscore. b WebThreadLockFromAnyThread works for me in both lldb and gdb. Now, this is Xcode 4.6, so if you're stuck on the older version I suppose it's possible that there's an issue in that version not present in 4.6.
You can try use nm command or class-dump tool to locate the module.
Most likely there are no symbols you need because xcode by default produces a "release" build which if I am correct strips the symbols making the exec file much smaller. I am not sure how at the moment but you need to find the option to switch to "debug" build which will guarantee to have all those lovely symbols waiting for your analysis.
I've made an iPad App. I was able to run this App on my device and on simulator.
After I've updated several classes (which I tested in simulator) I wasn't able to run my App on my device. It gives no errors but just hangs when compiling.
I'm thinking it's something with a class which came out very large and has some mathematical functions inside (calculations of transforms etc.)
After a long runtime Xcode gives back this error (something about a 'clang error'):
Anyone has any experience with these kind of issues and could find a solution?
EDIT:
Within my viewdidload method i have set 112 float values (i.e. value = 12;) and save them (with NSUSerdefaults).
Only setting these values solved my problem. No idea why this was giving me compile errors. I'm thinking the mathematical functions (after setting the float values) took to much memory or CPU.
Did you try cleaning your build and rebuild again?
Menu > Product > Clean
close & reopen XCode, "Clean All Targets" then rebuild. It should work.
Clean your project, delete the app from you iPad and try again. Should work.
Hope it helps
Are you trying to "Build and Analyze" or an ad-hoc build or debug build?
If your code crashed because of any memory issues or bad access memory due to any infinite loop, try to enable NSZombieEnabled in your executable settings. It will point you to the code snippet where the code crashes.
To enable "NSZombieEnabled", go to
Edit Active Executables -> Arguments -> Variables in the environment -> Add name as "NSZombieEnabled" and value to "YES"
Hopes this helps.
I am hoping someone can help me. I have just started running xcode 4.01 and for some reason whenever I run an app, it does not stop on breakpoints or display the NSlog messages. I have a message in my viewDidLoad and it never shows. I even breakpoint on this log and the best I can get in the output window is:
pending breakpoint 1 - "universalTestAppDelegate_iPad.m:15" resolved
pending breakpoint 2 - "universalTestAppDelegate_iPhone.m:16" resolved
Actual code is:
-(void) viewDidload
{
NSLog("in viewDidLoad");
}
So it appears it sees the breakpoint but never stops on it. As I said, brand new to xcode 4 so any idea on what I am doing wrong? Uninstalled and reinstalled and still nothing. Also, if it means anything, in the Scheme to choose where to run, I can select IOS devie, iPad 43 simulator and iPhone 4.3 simulator. Tried both and still nothing. Why can't I select/see other versions of the IOS?
BTW: The above is because I do not have my iPad or iPhone connected. Thanks in advance for any and all help.
Geo...
Your method is just never called.
Make it
-(void) viewDidLoad
with big "L" and your chances of "breaking" will sky rocket. ;)
Two possibilities:
You don't have breakpoints turned on. Use the Product->Debug->Activate Breakpoints command to rectify this.
You have breakpoints turned on but you placed your breakpoints on lines that haven't been executed. If your log statement doesn't appear in the console, that would indicate that the method containing that statement isn't executing, so it's no surprise that the breakpoint on that line has no effect.
I had similar issue where the debugger would not stop on breakpoints in the simulator using Xcode 4C199. Turns out the simulator was just buggered and restarting it resolved the issue.
I also had the issue with XCode 3 where I had localized the name of the app to a set of Japanese characters. The debugger didn't like that. I solved that one by having english name for debug configuration and japanese name for release.
Is there any way to track variable changes or memory changes in Xcode? I'm looking for functionality like Visual Studio's data breakpoint.
I want to know where my object's view frame is being changed. I want to set a breakpoint at a member variable and run it. Then I could determine where it's changed.
Xcode uses gdb (or lldb, but that's another story) to implement its debugging functionality. gdb has the ability to set hardware watchpoints and hence so does Xcode.
This is a useful page for generic debugging of memory errors. Xcode's debugging console window is really just a gdb shell, you can type in commands as you please. The ever-helpful Quinn Taylor explains how to do so in this related post.
If you'd rather avoid interacting with gdb directly, you can right-click a variable in Xcode's debugging window and select "Watch Variable". Xcode will then alert you whenever your variable's value has been changed.
You can use hardware watchpoints.
You have to get the address of the variable you want to track (type p &my_var in gdb prompt).
It will print somehting like 0x12345678.
With gdb: type watch *(int *)0x12345678.
With lldb: watch set expression (int *)0x12345678 (or w s e (int *)0x12345678)
This assumes your variable is an int. It will create an hardware watchpoint on this address.
Hope this helps.
Yes.
Under the Run menu there is "Debugger" which provides a visual frontend to gdb.
Also, there is a breakpoint button next to the Build and Run button. You can click that and manage your breakpoints under Run > Manage Breakpoints.
I know this post is old but in case you are still wondering I posted a detailed answer here: In XCode 6 how can you set a watchpoint without stopping execution?
I'm programming an application in Objective-C and I'm getting this error:
MyApp(2121,0xb0185000) malloc: *** error for object 0x1068310: double free
*** set a breakpoint in malloc_error_break to debug
It is happening when I release an NSAutoreleasePool and I can't figure out what object I'm releasing twice.
How do I set his breakpoint?
Is there a way to know what is this "object 0x1068310"?
When an object is "double-freed", the most common cause is that you're (unnecessarily) releasing an autoreleased object, and it is later autoreleased when the containing autorelease pool is emptied.
I've found that the best way to track down the extra release is to use the NSZombieEnabled environment variable for the affected executable in Xcode. For a quick rundown of how to use it, check out this CocoaDev wiki page. (In addition to this page, Apple has documented some incredibly obscure yet useful tips for debugging code in Xcode, some of which have saved my bacon more than a few times. I suggest checking out this Technical Note on developer.apple.com — link jumps to the section on Cocoa's Foundation framework).
Edit: You can often track the offending object down within the Xcode debugger, but it's often much easier if you use Instruments to assist you. From Xcode, choose Run → Start With Performance Tool → Object Allocations and you should be able to trace the offending object back to where it was created. (This will work best if you're enabled zombies as discussed above.) Note: Snow Leopard adds a Zombies tool to Instruments, accessible from the Run menu as well. Might be worth the $29 alone! ;-)
There is also a related SO question here.
You'll find out what the object is when you break in the debugger. Just look up the call stack and you will find where you free it. That will tell you which object it is.
The easiest way to set the breakpoint is to:
Go to Run -> Show -> Breakpoints (ALT-Command-B)
Scroll to the bottom of the list and add the symbol malloc_error_break
I just want to add my experience in addition to the answer of Quinn Taylor.
In one of my apps, I have to parse and save data into core data objects and later on get these objects to display on the views. In fact, the app works just fine and does not crash at all, until I tried to do a stress test of navigating back and forth multiple times, tried to open multiple views as fast as possible. The app crashes with the above message.
I have tried all the methods that Quinn suggested in his answer and still failed to find out where was the exact cause.
I set NSZombieEnabled=YES, and NSStackLogging=YES, ran the command shell malloc_history to find out why, but still no luck. It always points out to where I save the data into core data objects, in fact, I have checked thousand times the over released objects there, nothing odd.
Running in Instruments with various tools(Allocations, Leaks, etc...) still did not help. Enable the Guard Malloc still got nothing.
Final rescue: I tried to come back to the views where the objects were taken from Core Data and sent a retain message to all of these objects, and took note to these changes. It solved the issue!!!
So, I found out that I failed to retain one, that's exactly the cause. Just want to share my experience so you have another rescue for your app.
Open up the debugger console by pressing Cmd+Shift+R. There, type
break malloc_error_break
to set a breakpoint at the beginning of the malloc_error_break function.
If you want to find out what object is located at address 0x1068310, you can type the following into the debugger console:
print-object 0x1068310
Of course, you have to do this while the object is still alive -- if the object has already been freed by the time you do this, then this will not work.
Please find the below steps for how to find the object which is free and crash the application.
1) Click on the "Breakpoint navigator". 2) Then click on the
"+" button which is below. 3) Add the "Symbolic
Breakpoint..." from the list. 4) Add the
"malloc_error_break" keyword on the "Symbol" option.
Or you can also refer the below GIF presentation.
For me the issue was solved by
(gdb) call (void)_CFAutoreleasePoolPrintPools()
right after the crash. The address at the top of the stack was the address of the culprit. Threw in a retain and voila.
The address given in the log message did not get me anywhere. It never showed up in any of the various Instrumets. Apparently a pointer to some internal data which had already been freed.
Adding a symbolic breakpoint in Xcode 4
Just an update to make this relevant to Xcode 4...
From the Xcode 4 User Guide:
To add a symbolic breakpoint . . .
In the bottom-left corner of the breakpoint navigator, click the Add
button.
Choose Add Symbolic Breakpoint.
Enter the symbol name in the
Symbol field.
Click Done.
This is what the malloc_error_break breakpoint looks like in the Breakpoints window in Xcode.
Need to check the boxes to make it work.
alt text http://www.martijnthe.nl/wp-content/uploads/2009/08/Afbeelding-1.png
Check your classes and look under the dealloc method. Make sure you care calling [super dealloc].
I had this exact same problem and found out I was calling [self dealloc] instead. Just not paying attention.
In Xcode, click left of the line number to set a breakpoint. Then you can launch it by doing a "Build and Debug".
It is recommended to not have object that you create be autorelease since memory is a commodity on the iPhone. Apple recommends explicitly calling release.
To find these kinds of memory and pointer problems in general, you want to run your code against a runtime memory error checker like Valgrind. This should be able to point out lots of things your code is doing wrong, beyond those that cause it to crash.
Valgrind can work on OSX (though it says it's "unsupported and incomplete and buggy"), and with a little hacking someone got it to work on iPhone SDK executables.
Even better you can try Instruments, which is part of XCode. There's a tutorial for running it here.
If malloc_error_break is not helping...
The best way to solve this error is to run instruments with the NSZombies turned on. Instruments will flag you when the Zombie is messaged and you can trace directly back to the line of code.
Snow Leopard required, what a lifesaver though!
This is usually caused by some inspector, such as safari or safari preview. Refer to post or post and question.
Remove the select of AutoMatically Show Web ...., will remove this issue.
Note, just close safari or safari preview will not remove this issue. And you have to deselect both of safari and safari preview.
If this will not do, refer to this answer or post to debug it.