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Editorial Team
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Asked: 2026-06-12T02:40:59+00:00

Assume that a cocoa app must execute some vitally important objective-c operation before it

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Assume that a cocoa app must execute some vitally important objective-c operation before it exits (for any reason—crash or quit).

Is it possible to ensure the execution of arbitrary objective-c code in response to every crash event? (SIGINT, SIGBUS, SIGSEGV, etc, ignoring the “uncatchables” (SIGSTOP, SIGKILL, bolt of lightning, etc.))

It would be helpful to know what your hooks are trying to do.

For example: let’s say that for the app to operate, it absolutely must change the value of some mutable system-wide configuration variable X. On launch, the app takes a snapshot of X’s current state and then modifies it. When the app exits successfully, it just restores X to the stashed, original value before terminating. My question is this: is it possible to ensure that X gets restored even if the app crashes?

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1 Answer

  1. Editorial Team

    The short answer is no.

    A longer answer is still no, but you can minimise the opportunity for not being able to reset you system-wide mutable configuration variable. In outline:

    • On startup have your application spawn a faceless background process;
    • The faceless background process should mutate your variable and then wait (as in wait(2) & friends) till its parent expires;
    • On expiry of its parent it resets the variable and then expires itself.

    Your faceless background app should be short and simple, and therefore hopefully robust. It’s far from foolproof, or safe against a user with infanticide on their minds, but it narrows the opportunities for thwarting the reset of your variable.

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