Played around with the file locking and discovered to my chagrin that

whenever a process writes a cell to disk, it immediately releases the
file lock it had on that cell, which is clearly not the intent of file
locking.  Fixed this issue.  On a related topic, revised the "cellname
writeable" command so that it can make a cell editable even if the cell
has an advisory lock and cannot be made writeable.  Perhaps there should
be a clearer distinction here between "writeable" and "editable".  Also:
Reconsidered the previous commit, which removed the "--disable-locking"
from the configuration options.  Because some operating systems may not
implement fnctl()-based file locking (Cygwin, for one, apparently doesn't),
it is still useful to be able to completely remove the function, in case
the operating system will fail to recognize the fnctl() values in the
code.  Now, file locking behavior can be permanently removed through the
configuration option, or temporarily disabled from the command line.

commands/CmdCD.c

@@ -1108,22 +1108,31 @@ CmdCellname(w, cmd)
 		else if (subopt >= 4)
 		{
 		    /* Check if file is already read-write */
+#ifdef FILE_LOCKS
+		    if (!(cellDef->cd_flags & CDNOEDIT) && (cellDef->cd_fd != -1))
+#else
 		    if (!(cellDef->cd_flags & CDNOEDIT))
+#endif
 			break;
 
 		    /* Make file read-write */
-
 #ifdef FILE_LOCKS
 		    if (cellDef->cd_fd == -1)
 			dbReadOpen(cellDef, NULL, TRUE, NULL);
 
 		    if (cellDef->cd_fd == -1)
-			TxError("Overriding advisory lock held on cell %s\n",
+		    {
+			TxError("An advisory lock is held on cell %s.  Cell can now"
+				" be made editable but is not writeable.\n",
 				cellDef->cd_name);
+		    }
 #endif
-		    cellDef->cd_flags &= ~CDNOEDIT;
-		    WindAreaChanged(w, &w->w_screenArea);
-		    CmdSetWindCaption(EditCellUse, EditRootDef);
+		    if (cellDef->cd_flags & CDNOEDIT)
+		    {
+			cellDef->cd_flags &= ~CDNOEDIT;
+			WindAreaChanged(w, &w->w_screenArea);
+			CmdSetWindCaption(EditCellUse, EditRootDef);
+		    }
 		}
 		else	/* "cellname writeable false" */
 		{

commands/CmdLQ.c

@@ -54,8 +54,10 @@ void CmdPaintEraseButton();
 
 extern Label *DefaultLabel;
 
+#ifdef FILE_LOCKS
 /* See the "locking" command */
 extern bool FileLocking;
+#endif
 
 /*
  * ----------------------------------------------------------------------------
@@ -541,6 +543,7 @@ keepGoing(use, clientdata)
     return 0;	/* keep the search going */
 }
 
+#ifdef FILE_LOCKS
 /*
  * ----------------------------------------------------------------------------
  *
@@ -604,6 +607,7 @@ CmdLocking(w, cmd)
 	FileLocking = (option <= 4) ? FALSE : TRUE;
     }
 }
+#endif	/* FILE_LOCKS */
 
 /*
  * ----------------------------------------------------------------------------

database/DBio.c

@@ -69,6 +69,10 @@ static char rcsid[] __attribute__ ((unused)) = "$Header: /usr/cvsroot/magic-8.0/
 
 extern char *Path;
 
+#ifdef FILE_LOCKS
+extern bool FileLocking;
+#endif
+
 /* Suffix for all Magic files */
 char *DBSuffix = ".mag";
 
@@ -3223,18 +3227,23 @@ DBCellWrite(cellDef, fileName)
      * figure out why.
      */
 
-    if(cellDef->cd_flags & CDNOEDIT)
+    if (cellDef->cd_flags & CDNOEDIT)
     {
-#ifdef FILE_LOCKS
-	TxPrintf("File %s is locked by another user or "
-		"is read_only and cannot be written\n", realname);
-#else
 	TxPrintf("File %s is read_only and cannot be written\n", realname);
-#endif
 	freeMagic(realname);
 	return(FALSE);
     }
 
+#ifdef FILE_LOCKS
+    if (cellDef->cd_fd == -1)
+    {
+	TxPrintf("File %s is locked by another user and "
+		"cannot be written\n", realname);
+	freeMagic(realname);
+	return(FALSE);
+    }
+#endif
+
     /* Check if the .mag file exists.  If not, we don't need to deal	*/
     /* with temporary file names.					*/
     exists = (access(expandname, F_OK) == 0) ? TRUE : FALSE;
@@ -3321,17 +3330,6 @@ DBCellWrite(cellDef, fileName)
 		    tmpname, expandname, expandname, cellDef->cd_name, tmpname);
 	    goto cleanup;
 	}
-
-#ifdef FILE_LOCKS
-	else
-	{
-	    bool dereference = (cellDef->cd_flags & CDDEREFERENCE) ? TRUE : FALSE;
-	    /* Re-aquire the lock on the new file by opening it. */
-	    if (DBCellRead(cellDef, NULL, TRUE, dereference, NULL) == FALSE)
-		return FALSE;
-	}
-#endif
-
     }
     else if (exists)
     {
@@ -3408,7 +3406,14 @@ DBCellWrite(cellDef, fileName)
     result = TRUE;
     {
 	struct stat thestat;
-	realf = fopen(expandname, "r");
+	bool is_locked;
+#ifdef FILE_LOCKS
+	if (FileLocking)
+	    realf = flock_open(expandname, "r", &is_locked);
+	else
+#endif
+	    realf = fopen(expandname, "r");
+
 	if (realf == NULL)
 	{
 	    cellDef->cd_flags |= CDMODIFIED;
@@ -3416,13 +3421,20 @@ DBCellWrite(cellDef, fileName)
 	}
 	else
 	{
-	    fstat(fileno(realf),&thestat);
+	    int fd = fileno(realf);
+	    fstat(fd, &thestat);
 	    if (thestat.st_size != DBFileOffset)
 	    {
 		cellDef->cd_flags |= CDMODIFIED;
 		TxError("Warning: I/O error in writing file \"%s\"\n", expandname);
 	    }
-	    fclose(realf);
+
+#ifdef FILE_LOCKS
+	    if (FileLocking && (is_locked == FALSE))
+		cellDef->cd_fd = fd;
+	    else
+#endif
+		fclose(realf);
 	}
 	realf = NULL;
     }

dbwind/DBWcommands.c

@@ -46,7 +46,10 @@ extern void CmdDelete(), CmdDown(), CmdDrc(), CmdDrop(), CmdDump();
 extern void CmdEdit(), CmdElement(), CmdErase(), CmdExpand(), CmdExtract();
 extern void CmdFeedback(), CmdFill(), CmdFindBox(), CmdFindLabel(), CmdFlush();
 extern void CmdGetcell(), CmdGrid(), CmdIdentify();
-extern void CmdLabel(), CmdLoad(), CmdLocking();
+extern void CmdLabel(), CmdLoad();
+#ifdef FILE_LOCKS
+extern void CmdLocking();
+#endif
 extern void CmdMove(), CmdNetlist(), CmdOrient(), CmdPaint(), CmdPath();
 extern void CmdPlow(), CmdPolygon(), CmdPort(), CmdProperty();
 extern void CmdRandom(), CmdSave(), CmdScaleGrid(), CmdSee();
@@ -369,9 +372,11 @@ DBWInitCommands()
     WindAddCommand(DBWclientID,
 	"load [cellname]	load a cell into a window",
 	CmdLoad, FALSE);
+#ifdef FILE_LOCKS
     WindAddCommand(DBWclientID,
 	"locking [enable|disable]	enable or disable file locking",
 	CmdLocking, FALSE);
+#endif
     WindAddCommand(DBWclientID,
 	"move [dir [amount]]	OR\n"
 	"move to x y		move box and selection, either by amount\n\

scripts/configure

@@ -6844,8 +6844,15 @@ else
 fi
 
 
-if test "x$enable_locking" = "xno" ; then
-  echo "File locking no longer set during configuration;  ignoring option."
+if test "x$enable_locking" = "xyes" ; then
+  case $target in
+    *cygwin*)
+	;;
+    *)
+	$as_echo "#define FILE_LOCKS 1" >>confdefs.h
+
+	;;
+  esac
 fi
 
 # Check whether --enable-calma was given.

scripts/configure.in

@@ -935,8 +935,14 @@ AC_ARG_ENABLE(locking,
 [],
 [enable_locking=yes])
 
-if test "x$enable_locking" = "xno" ; then
-  echo "File locking no longer set during configuration;  ignoring option."
+if test "x$enable_locking" = "xyes" ; then
+  case $target in
+    *cygwin*)
+	;;
+    *)
+	AC_DEFINE(FILE_LOCKS)
+	;;
+  esac
 fi
 
 AC_ARG_ENABLE(calma,

utils/flock.c

@@ -11,6 +11,8 @@
  *-------------------------------------------------------------------------
  */
 
+#ifdef FILE_LOCKS
+
 #include <unistd.h>
 #include <fcntl.h>
 
@@ -164,3 +166,5 @@ FILE *flock_open(filename, mode, is_locked)
 done:
     return f;
 }
+
+#endif	/* FILE_LOCKS */

utils/path.c

@@ -46,7 +46,9 @@ static char rcsid[] __attribute__ ((unused)) = "$Header: /usr/cvsroot/magic-8.0/
 static HashTable expansionTable;
 static bool noTable = TRUE;
 
+#ifdef FILE_LOCKS
 bool FileLocking = TRUE;
+#endif
 
 /* Limit on how long a single file name may be: */
 
@@ -456,9 +458,11 @@ PaLockOpen(file, mode, ext, path, library, pRealName, is_locked)
 	p2 = file;
 	if (PaExpand(&p2, &p1, MAXSIZE) < 0) return NULL;
 
+#ifdef FILE_LOCKS
 	if (FileLocking)
 	    return flock_open(realName, mode, is_locked);
 	else
+#endif
 	    return fopen(realName, mode);
     }
 
@@ -475,9 +479,11 @@ PaLockOpen(file, mode, ext, path, library, pRealName, is_locked)
 	(void) strncpy(realName, file, MAXSIZE-1);
 	realName[MAXSIZE-1] = '\0';
 
+#ifdef FILE_LOCKS
 	if (FileLocking)
 	    return flock_open(realName, mode, is_locked);
 	else
+#endif
 	    return fopen(realName, mode);
     }
 
@@ -487,9 +493,11 @@ PaLockOpen(file, mode, ext, path, library, pRealName, is_locked)
     {
 	if (*realName == 0) continue;
 
+#ifdef FILE_LOCKS
 	if (FileLocking)
 	    f = flock_open(realName, mode, is_locked);
 	else
+#endif
 	    f = fopen(realName, mode);
 
 	if (f != NULL) return f;
@@ -506,9 +514,11 @@ PaLockOpen(file, mode, ext, path, library, pRealName, is_locked)
     if (library == NULL) return NULL;
     while (nextName(&library, file, realName, MAXSIZE) != NULL)
     {
+#ifdef FILE_LOCKS
 	if (FileLocking)
 	    f = flock_open(realName, mode, is_locked);
 	else
+#endif
 	    f = fopen(realName, mode);
 
 	if (f != NULL) return f;

utils/utils.h

@@ -54,7 +54,9 @@ extern bool StrIsNumeric(char *);
 
 extern int SetNoisyBool(bool *, char *, FILE *);
 
+#ifdef FILE_LOCKS
 extern FILE *flock_open();
+#endif
 
 /* The following macro takes an integer and returns another integer that
  * is the same as the first except that all the '1' bits are turned off,