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futex.2: Add overview of priority inheritance
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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man2/futex.2
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man2/futex.2
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@ -638,6 +638,22 @@ the low-priority process from the CPU.
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Consequently, the low-priority process makes no progress toward
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Consequently, the low-priority process makes no progress toward
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releasing the lock, and the high-priority process remains blocked.
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releasing the lock, and the high-priority process remains blocked.
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Priority inheritance is a mechanism for dealing with
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the priority-inversion problem.
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With this mechanism, when a high-priority process becomes blocked
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by a lock held by a low-priority process,
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the latter's priority is temporarily raised to that of the former,
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so that it is not preempted by any intermediate level processes,
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and can thus make progress toward releasing the lock.
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To be effective, priority inheritance must be transitive,
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meaning that if a high-priority process blocks on a lock
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held by a lower-priority process that is itself blocked by lock
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held by another intermediate-priority process
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(and so on, for chains of arbitrary length),
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then both of those process
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(or more generally, all of the processes in a lock chain)
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have their priorities raised to be the same as the high-priority process.
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.\" FIXME ===== Start of adapted Hart/Guniguntala text =====
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.\" FIXME ===== Start of adapted Hart/Guniguntala text =====
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.\" The following text is drawn from the Hart/Guniguntala paper,
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.\" The following text is drawn from the Hart/Guniguntala paper,
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.\" but I have reworded some pieces significantly. Please check it.
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.\" but I have reworded some pieces significantly. Please check it.
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