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I would like to know what's the best way, in term of efficiency (cpu/memory usage), to temporarily suspend/bypass a low level mouse/keyboard hook.

The current solution I found is to set a global var, "doHook" in the exemple, test it in the hook proc and if not set just let it pass with CallNextHookEx like that :

    if ((nCode < 0) || (!doHook))
    {
        return CallNextHookEx(NULL, nCode, wParam, lParam);
    }

Is it a good solution ? a better way ?

Thanks

jj.jpnt
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1 Answers1

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You have 2 options:

  • Removing the hook entirely by calling UnhookWindowsHookEx.
  • Leaving the hook in place and skipping normal operation.

Low level keyboard and mouse hooks are somewhat costly, since they introduce additional context switches for handling input events:

The [...] hook is not injected into another process. Instead, the context switches back to the process that installed the hook and it is called in its original context. Then the context switches back to the application that generated the event.

Essentially, your do-nothing hook still uses up thousands of clock cycles for context switching, for all input events. To minimize overall impact you should consider uninstalling the hook entirely and reinstalling it when necessary.

IInspectable
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  • For the program in which I'm currently doing that I need to enable the hook at the speed of light so I think entirely uninstalling and reinstalling the hook is not an option as I think it's far more slow to restart than with my solution (or maybe it isn't as slow as I think ?). I thought of another solution : isn't it possible to create a thread dedicated to the hook and suspend/pause it then resume it ? (I'm still quite new to threads) Shouldn't it be possible ? – jj.jpnt Jan 27 '14 at 04:39
  • A suspended thread is just that: A thread that will not be scheduled for execution. There is no facility that would skip this particular thread when executing a hook chain. Since you are concerned about performance you should probably use a profiler, to measure the current performance, compare different implementations, and make an informed decision. – IInspectable Jan 27 '14 at 13:15