Initial import of the CDE 2.1.30 sources from the Open Group.

cde/lib/tt/mini_isam/ismngfcb.c

@@ -0,0 +1,214 @@
+/*%%  (c) Copyright 1993, 1994 Hewlett-Packard Company			 */
+/*%%  (c) Copyright 1993, 1994 International Business Machines Corp.	 */
+/*%%  (c) Copyright 1993, 1994 Sun Microsystems, Inc.			 */
+/*%%  (c) Copyright 1993, 1994 Novell, Inc. 				 */
+/*%%  $XConsortium: ismngfcb.c /main/3 1995/10/23 11:42:28 rswiston $ 			 				 */
+#ifndef lint
+static char sccsid[] = "@(#)ismngfcb.c 1.4 89/07/17 Copyr 1988 Sun Micro";
+#endif
+/*
+ * Copyright (c) 1988 by Sun Microsystems, Inc.
+ */
+
+/*
+ * ismngfcb.c
+ *
+ * Description: 
+ *	Manager of open FCB blocks.
+ *
+ * This module keeps track of usage of the FCB blocks and finds a victim
+ * on LRU basis.
+ * It also provides associative access to the FCB by their isfhandles.
+ *
+ */
+#include "isam_impl.h"
+
+
+#define FCBHASHSIZE	101		     /* Should be a prime for best hash */
+
+#if  (MAXFCB_UNIXFD > FCBHASHSIZE)
+/* 
+ * Cause a syntax error. FCBHASHSIZE must be increased to be > MAXFCB_UNIXFD.
+ * A good estimate is a prime approximately equal (2 * MAXFCB_UNIXFD).
+ */
+MUST INCREASE FCBHASHSIZE
+#endif
+
+struct hashtable {
+    Bytearray	isfhandle;
+    Fcb		*fcb;
+    long	mrused;			     
+} hashtable [FCBHASHSIZE];
+#define unused(entry) ((entry).fcb == NULL)
+
+static int _hashisfhandle();
+
+static mrused_last = 0;			     /* stamp generator */
+
+
+/*
+ * _mngfcb_insert(fcb, isfhandle)
+ *
+ * Insert new FCB entry.
+ */
+
+void
+_mngfcb_insert(fcb, isfhandle)
+    Fcb		*fcb;
+    Bytearray	*isfhandle;
+{
+    int			hashval = _hashisfhandle(isfhandle);
+    register int  	ind;
+    int			ntries;
+
+    /* Try to find an unused entry in the hash table. */
+    ind = hashval;
+    for (ntries = 0; ntries < FCBHASHSIZE; ntries++) {
+	if (unused(hashtable[ind]))
+	    break;
+	if (++ind == FCBHASHSIZE)
+	    ind = 0;			     /* Wrap the table */
+    }
+
+    if (ntries == FCBHASHSIZE) {
+	_isfatal_error("FCB hash table overflow");
+    }
+	
+    /*
+     * Create an entry at the index ind.
+     * Duplicate the file handle and mark the entry with the current stamp.
+     */
+    hashtable[ind].isfhandle = _bytearr_dup(isfhandle);
+    hashtable[ind].fcb = fcb;
+    hashtable[ind].mrused = mrused_last++;
+}
+
+
+/*
+ * fcb = _mngfcb_find(isfhandle)
+ *	
+ * Return a pointer to the FCB, or NULL if the FCB is not found.
+ * If the FCB is found, it is "touched" for the LRU algorithm purpose.
+ */
+
+Fcb *
+_mngfcb_find(isfhandle)
+    Bytearray	*isfhandle;
+{
+    int			hashval = _hashisfhandle(isfhandle);
+    register int  	ind;
+    int			ntries;
+
+    /* Find the entry. */
+    ind = hashval;
+    for (ntries = 0; ntries < FCBHASHSIZE; ntries++) {
+	if (_bytearr_cmp(&hashtable[ind].isfhandle, isfhandle) == 0)
+	    break;
+	if (++ind == FCBHASHSIZE)
+	    ind = 0;			     /* Wrap the table */
+    }
+
+    if (ntries == FCBHASHSIZE) {
+	return (NULL);			     /* Not found */
+    } 
+    else {
+
+	/*
+	 * Mark the entry with the current stamp.
+	 */
+	hashtable[ind].mrused = mrused_last++;
+	return hashtable[ind].fcb;
+    }
+}
+
+/*
+ * _mngfcb_delete(isfname)
+ *
+ * Delete an entry.
+ */
+
+void
+_mngfcb_delete(isfhandle)
+    Bytearray	*isfhandle;
+{
+    int			hashval = _hashisfhandle(isfhandle);
+    register int  	ind;
+    int			ntries;
+
+    /* Find the entry */
+    ind = hashval;
+    for (ntries = 0; ntries < FCBHASHSIZE; ntries++) {
+	if (_bytearr_cmp(&hashtable[ind].isfhandle, isfhandle) == 0)
+	    break;
+	if (++ind == FCBHASHSIZE)
+	    ind = 0;			     /* Wrap the table */
+    }
+
+    if (ntries == FCBHASHSIZE) {
+	_isfatal_error("_mngfcb_delete cannot find entry");
+    } 
+    else {
+
+	/*
+	 * Clear the entry.
+	 */
+	_bytearr_free(&hashtable[ind].isfhandle);
+	memset ((char *) &hashtable[ind], 0, sizeof(hashtable[ind]));
+    }
+}
+
+
+/*
+ * isfhandle = _mngfcb_victim()
+ *
+ * Find LRU used FCB.
+ */
+
+Bytearray *
+_mngfcb_victim()
+{
+    int			victim_ind = -1;
+    long		victim_time = 0;     /* Assign to shut up lint */
+    register int	i;
+
+    for (i = 0; i < FCBHASHSIZE; i++) {
+
+	if (unused(hashtable[i]))	     /* Skip empty slots in table */
+	    continue;
+	
+	if (victim_ind == -1 || victim_time > hashtable[i].mrused) {	
+	    victim_ind = i;
+	    victim_time = hashtable[i].mrused;
+	}
+    }
+    return ((victim_ind == -1) ? NULL : &hashtable[victim_ind].isfhandle);
+}
+
+
+/*
+ * _hashisfhandle(isfhandle)
+ *
+ * Hash isfhandle into an integer.
+ */
+
+Static int
+_hashisfhandle(isfhandle)
+    Bytearray		*isfhandle;
+{
+    register char	*p;
+    register unsigned	h, g;
+    register int	len;
+
+    len = isfhandle->length;
+    p = isfhandle->data;
+    h = 0;
+
+    while (len-- > 0) {
+	h = (h << 4) + (*p++);
+	if (g = h&0xf0000000) {
+	    h = h ^ (g >> 24);
+	    h = h ^ g;
+	}
+    }
+    return (h % FCBHASHSIZE);
+}