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    possible.</para>
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    possible.</para>
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    <formalpara>
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    <formalpara>
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      <title>Thread states</title>
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      <title>Thread states</title>
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      <para>In each moment, a thread exists in one of five possible thread
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      <para>In each moment, a thread exists in one of six possible thread
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      states. When the thread is created and first readied into the
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      states. When the thread is created and first readied into the
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      scheduler's run queues or when a thread is migrated to a new processor,
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      scheduler's run queues or when a thread is migrated to a new processor,
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      it is put into the <code>Entering</code> state. After some time, the
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      it is put into the <constant>Entering</constant> state. After some time,
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      scheduler picks up the thread and starts executing it. A thread being
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      the scheduler picks up the thread and starts executing it. A thread
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      currently executed on a processor is in the <code>Running</code> state.
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      being currently executed on a processor is in the
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      From there, the thread has three possibilities. It either runs until it
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      <constant>Running</constant> state. From there, the thread has three
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      is preemtped, in which case the state changes to <code>Ready</code>,
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      possibilities. It either runs until it is preemtped, in which case the
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      state changes to <constant>Ready</constant>, goes to the
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      goes to the <code>Sleeping</code> state by going to sleep or enters the
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      <constant>Sleeping</constant> state by going to sleep or enters the
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      <code>Exiting</code> state when it reaches termination.<figure>
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      <constant>Exiting</constant> state when it reaches termination. When the
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      thread exits, its kernel structure usually stays in memory, until the
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      thread is detached by another thread using <code>thread_detach</code>
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      function. Terminated but undetached threads are in the
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      <constant>Undead</constant> state. When the thread is detached or
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      detaches itself during its life, it is destroyed in the
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      <constant>Exiting</constant> state and the <constant>Undead</constant>
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      state is not reached.<figure>
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          <title>Transitions among thread states.</title>
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          <title>Transitions among thread states.</title>
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          <mediaobject id="thread_states" xreflabel="">
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          <mediaobject id="thread_states" xreflabel="">
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            <imageobject role="html">
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            <imageobject role="html">
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              <imagedata fileref="images/thread_states.png" format="PNG" />
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              <imagedata fileref="images/thread_states.png" format="PNG" />