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InterlockedExchangeAdd equivalent

Doug Price
Note: This was originally posted on 11th February 2013 at http://forums.arm.com

I'm porting a Windows application to an ARM® Cortex-A9 based system running Ubuntu 12.04 and I need something equivalent the Windows function InterlockedExchangeAdd().  Is there a function like this available for ARM?  If not, can anyone provide some equivalent assembly code?
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  • Arm Employee Badge
    Note: This was originally posted on 13th February 2013 at http://forums.arm.com

    It depends what you are using it for TBH. If you are using it like a spinlock (e.g., incref to lock, decref to unlock) then you need barriers after the lock before you touch the memory it is protecting (ensure that the lock is committed before other instructions in the instruction stream can touch the memory) and before the unlock (ensure you've committed data it is protecting to memory before you release the lock). If you don't then you risk race conditions and trampled data (and much painful debugging - trust me).

    If you are just using it like a reference count then you might get away with it ;)
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  • Arm Employee Badge
    Note: This was originally posted on 13th February 2013 at http://forums.arm.com

    It depends what you are using it for TBH. If you are using it like a spinlock (e.g., incref to lock, decref to unlock) then you need barriers after the lock before you touch the memory it is protecting (ensure that the lock is committed before other instructions in the instruction stream can touch the memory) and before the unlock (ensure you've committed data it is protecting to memory before you release the lock). If you don't then you risk race conditions and trampled data (and much painful debugging - trust me).

    If you are just using it like a reference count then you might get away with it ;)
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