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<title>7.7 Semaphores</title>

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<h2>
  <a name="1205811"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">7.7 	 Semaphores</font>
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  <a name="1205812"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Semaphores provide a means of controlling the execution of concurrent processes. An n-valued semaphore ensures that from the set of processes that are waiting on that semaphore, at most n can run concurrently. If a process has a critical piece of code which must only execute when the semaphore allows it to, then the code waits on the semaphore before commencing, and signals to the semaphore when it has finished.</font>
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  <a name="1205813"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">The ST20-C2 provides an efficient implementation of an n-valued semaphore for processes. <strong>signal</strong> and <strong>wait</strong> instructions, shown in <a href="conc_pr8.htm#1205834"><font  color="#0000ff" face="Verdana, Arial, Helvetica, sans-serif"><i>Table

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