OH

Section: User Commands (1)
Updated: March 28, 1996
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NAME

oh - print object history

SYNOPSIS

oh pid mode [-subst old new]

DESCRIPTION

oh records all of the retain and release activity for a given process and can list all of the stacks that involve a given object. Additionally, oh can pinpoint the biggest generators of autorelease. Using oh on a process makes it run much more slowly, so you should use it sparingly.

oh takes two arguments: a process ID and a mode. The process ID is the ID of the process that you want to record activity about. The mode is any one of the following:

start: Start recording information about the process.
stop: Stop recording information about the process.
autorelease: List all of the stacks that contain an autorelease message.
address: List all of the stacks that include a message allocating or deallocating the object at adddress.

OPTIONS

pid: The ID (obtained using pid(1)) of the process you want to gather information about.
mode: Is the action oh should take (see above).
-subst old new: Replaces the executable in path old with the executable in path new. This option is often used to replace a stripped version of the executable with a version that contains debugging symbols.

EXAMPLES

To use oh, start up the program that you want to analyze, obtain its process id, then execute:

: oh pid start

oh starts recording information about object allocation and deallocation. After oh has started recording, you can enter the address of an object like this:

: oh pid address

and oh displays the stacks, from oldest to newest, involving that object.

To stop recording with oh, enter:

: oh pid stop

You might find it useful to set the NSZombieEnabled environment variable to YES before starting up your program. This environment variable ensures that memory does not get reused, thus ensuring that any address you give to oh will be unique.

You can run oh in conjunction with gdb so that you can use gdb to easily obtain the address of an object. It's also useful to run oh in conjunction with leaks to help find a cause of a memory leak.

BUGS

oh ignores objects that have overridden retain and release.

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Time: 00:59:48 GMT, September 26, 2024