X-Git-Url: https://codewiz.org/gitweb?a=blobdiff_plain;f=kern%2Fsem.c;fp=kern%2Fsem.c;h=98646e939047200abe5cd7bf64876aaafc3812c2;hb=1cc167e20f21d2e81527ca47ccd4a21a6198f86f;hp=0000000000000000000000000000000000000000;hpb=37d3acaa622b7f695ce57578e56311d031a22d22;p=bertos.git

diff --git a/kern/sem.c b/kern/sem.c
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+/*!
+ * \file
+ * <!--
+ * Copyright 2001,2004 Develer S.r.l. (http://www.develer.com/)
+ * Copyright 1999,2000,2001 Bernardo Innocenti <bernie@develer.com>
+ * All Rights Reserved.
+ * -->
+ *
+ * \brief Semaphore based synchronization services.
+ *
+ * \version $Id$
+ *
+ * \author Bernardo Innocenti <bernie@develer.com>
+ */
+
+/*
+ * $Log$
+ * Revision 1.1  2004/05/23 17:27:00  bernie
+ * Import kern/ subdirectory.
+ *
+ */
+
+#include "sem.h"
+#include "proc.h"
+#include "proc_p.h"
+#include "signal.h"
+#include "hw.h"
+
+
+/*!
+ * \brief Initialize a Semaphore structure
+ */
+void sem_init(struct Semaphore *s)
+{
+	INITLIST(&s->wait_queue);
+	s->owner = NULL;
+	s->nest_count = 0;
+}
+
+
+/*!
+ * \brief Attempt to lock a semaphore without waiting.
+ *
+ * \return true in case of success, false if the semaphore
+ *         was already locked by someone else.
+ *
+ * \note   each call to sem_attempt() must be matched by a
+ *         call to sem_release().
+ */
+bool sem_attempt(struct Semaphore *s)
+{
+	DISABLE_INTS;
+	if ((!s->owner) || (s->owner == CurrentProcess))
+	{
+		s->owner = CurrentProcess;
+		s->nest_count++;
+		ENABLE_INTS;
+		return true;
+	}
+	ENABLE_INTS;
+	return false;
+}
+
+
+/*!
+ * \brief Lock a semaphore.
+ *
+ * If the semaphore is already owned by another process, the caller
+ * process will be enqueued into the waiting list and sleep until
+ * the semaphore is available.
+ *
+ * \note Each call to sem_obtain() must be matched by a
+ *       call to sem_release().
+ *
+ * \note This routine is optimized for highest speed in
+ *       the most common case: the semaphore is free or locked
+ *       by the calling process itself. Rearranging this code
+ *       is probably a bad idea.
+ */
+void sem_obtain(struct Semaphore *s)
+{
+	DISABLE_INTS;
+
+	/* Is the semaphore already locked by another process? */
+	if (s->owner && (s->owner != CurrentProcess))
+	{
+		/* Append calling process to the wait queue */
+		ADDTAIL(&s->wait_queue, (Node *)CurrentProcess);
+		ENABLE_INTS;
+
+		/* We will awake only when the current owner calls
+		 * ReleaseSemaphore(). Then, the semaphore will already
+		 * be locked for us.
+		 */
+		proc_schedule();
+	}
+	else
+	{
+		/* The semaphore is free: lock it */
+		s->owner = CurrentProcess;
+		s->nest_count++;
+		ENABLE_INTS;
+	}
+}
+
+
+/*!
+ * \brief Releases a lock on a previously locked semaphore.
+ *
+ * If the nesting count of the semaphore reaches zero,
+ * the next process waiting for it will be awaken.
+ *
+ * \note This routine is optimized for highest speed in
+ *       the most common case: the semaphore has been locked just
+ *       once and nobody else was waiting for it. Rearranging
+ *       this code is probably a bad idea.
+ */
+void sem_release(struct Semaphore *s)
+{
+	DISABLE_INTS;
+
+	/* Decremement nesting count and check if the semaphore
+	 * has been fully unlocked
+	 */
+	if (--s->nest_count == 0)
+	{
+		/* Disown semaphore */
+		s->owner = NULL;
+
+		/* Anybody still waiting for this semaphore? */
+		if (!ISLISTEMPTY(&s->wait_queue))
+		{
+			/* Give semaphore to the first applicant */
+			Process *proc = (Process *)s->wait_queue.head;
+			REMOVE((Node *)proc);
+			s->nest_count = 1;
+			s->owner = proc;
+			SCHED_ENQUEUE(proc);
+		}
+	}
+
+	ENABLE_INTS;
+}
+