Postgres95 1.01 Distribution - Virgin Sources

src/backend/port/hpux/tas.c.template

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+/*
+ * To generate tas.s using this template:
+ *	1. cc +O2 -S -c tas.c
+ *	2. edit tas.s:
+ *		- replace the LDW with LDCWX
+ * For details about the LDCWX instruction, see the "Precision
+ * Architecture and Instruction Reference Manual" (09740-90014 of June
+ * 1987), p. 5-38.
+ */
+
+int
+tas(lock)
+    int *lock;	/* LDCWX is a word instruction */
+{
+    /*
+     * LDCWX requires that we align the "semaphore" to a 16-byte
+     * boundary.  The actual datum is a single word (4 bytes).
+     */
+    lock = ((long) lock + 15) & ~15;
+
+    /*
+     * The LDCWX instruction atomically clears the target word and
+     * returns the previous value.  Hence, if the instruction returns
+     * 0, someone else has already acquired the lock before we tested
+     * it (i.e., we have failed).
+     *
+     * Notice that this means that we actually clear the word to set
+     * the lock and set the word to clear the lock.  This is the
+     * opposite behavior from the SPARC LDSTUB instruction.  For some
+     * reason everything that H-P does is rather baroque...
+     */
+    if (*lock) {	/* this generates the LDW */
+	return(0);	/* success */
+    }
+    return(1);    	/* failure */
+}