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On Thursday 24 July 2008, b.n. wrote: |
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> |
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> I jump here to relief my everlasting UNIX ignorance. |
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> |
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> What does it mean a process is "sleeping", technically? |
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It's a misnomer, it means "not running". |
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The cpu gives the illusion of executing many tasks simultaneously. In |
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reality, it is executing them one at a time and very rapidly (many |
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times a second) switching between them. |
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Normally at a given instant in time, one task is running per cpu. The |
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rest are mostly waiting their turn or sleeping. There are various OS |
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strategies for bringing this about - some rely on the task itself to |
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back out after a running for a short while, sometimes the OS kernel |
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enforces it, sometimes you have a combination. If everything is working |
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nicely, the end result is pretty much the same. |
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There's another state worthy of note - blocked. This is when a task is |
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waiting for something else to happen first (most often disk or network |
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I/O) so it won't try and execute till that other thing happens. This is |
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not the same as sleeping. Sleeping is spinning you wheels in idle, |
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blocked is a deliberate stop and sit back and wait. |
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hth |
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alan |
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-- |
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Alan McKinnon |
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alan dot mckinnon at gmail dot com |
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