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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
<html>
<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<link rel="home" href="http://developer.apple.com/">
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<link rel="stylesheet" type="text/css" href="../../documentation/css/adcstyle.css" title="fonts">
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<title>GrabBag - /FileAccess.c</title>
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<a href="http://developer.apple.com/">ADC Home</a> > <a href="../../referencelibrary/index.html">Reference Library</a> > <a href="../../samplecode/index.html">Sample Code</a> > <a href="../../samplecode/Carbon/index.html">Carbon</a> > <a href="../../samplecode/Carbon/idxHumanInterfaceToolbox-date.html">Human Interface Toolbox</a> > <A HREF="javascript:location.replace('index.html');">GrabBag</A> >
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<table width="680" border="0" cellpadding="0" cellspacing="0">
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<td><h1><div id="pagehead">GrabBag</div></h1></td>
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<h2>/FileAccess.c</h2>
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<p><strong>View Source Code:</strong>
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<option value="listing1.html">/CatSearchThread.c</option>
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<option value="listing3.html">/FileAccess.c</option>
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<option value="listing7.html">/Resources/English.lproj/GrabBag Help/index.html</option></select>
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<p><strong><a href="GrabBag.zip">Download Sample</a></strong> (“GrabBag.zip”, 252.5K)<BR>
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<!--googleon: index -->
<pre class="sourcecodebox">/* File: FileAccess.c Contains: The underlying BSD layer on Mac OS X 10.0->10.1 does not implement "mandatory" locks on files. This means that if one application opens a file for exclusive write access, it really doesn't have "exclusive" access, and another application can write over the file. This file contains some basic routines to implement a technique to allow exclusive access between applications. This technique used "lockfiles" to signal a file is already open. We store the PSN within the "lockfile" to guard against applications crashing with open files. This method should also work between classic and carbon applications. This file demonstrates how to override FSpOpenDF and FSClose to utilize this method of advisory locks. There are many other variants of the Open cals including: PBHOpenDF, PBHOpenRF, PBHOpen, PBOpenFork, FSOpenFork, HOpen, etc. "Advisory" locks via fcntl() and flock() are implemented within the BSD layer and therefore would only be available from native applications. For more info on "Advisory" locks use the man pages or reference "Advanced Programming in the UNIX Environment", by Richard Stevens, pages 367-382, or contact Developer Technical Support. Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple Computer, Inc. ("Apple") in consideration of your agreement to the following terms, and your use, installation, modification or redistribution of this Apple software constitutes acceptance of these terms. If you do not agree with these terms, please do not use, install, modify or redistribute this Apple software. In consideration of your agreement to abide by the following terms, and subject to these terms, Apple grants you a personal, non-exclusive license, under Apple's copyrights in this original Apple software (the "Apple Software"), to use, reproduce, modify and redistribute the Apple Software, with or without modifications, in source and/or binary forms; provided that if you redistribute the Apple Software in its entirety and without modifications, you must retain this notice and the following text and disclaimers in all such redistributions of the Apple Software. Neither the name, trademarks, service marks or logos of Apple Computer, Inc. may be used to endorse or promote products derived from the Apple Software without specific prior written permission from Apple. Except as expressly stated in this notice, no other rights or licenses, express or implied, are granted by Apple herein, including but not limited to any patent rights that may be infringed by your derivative works or by other works in which the Apple Software may be incorporated. The Apple Software is provided by Apple on an "AS IS" basis. APPLE MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS. IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION, MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Copyright © 2001 Apple Computer, Inc., All Rights Reserved*/#ifdef __APPLE_CC__#include <Carbon/Carbon.h>#else#include <Carbon.h>#endif#include <stdio.h>#include <string.h>#include "Main.h"static OSErr WriteLockTheFile( FSSpec *spec );static OSErr OpenGrabBagSharedFile( short permission, short *refNum );static OSErr ReadFromGrabBagSharedFile( WindowRef window );static OSErr WriteToGrabBagSharedFile( WindowRef window );static void UpdateErrorMessage( WindowRef window, char *errMsg, OSErr err );extern GlobalsStruct g;void OpenGrabBagSharedFileWithWriteAccess( WindowRef window ){ OSErr err; err = OpenGrabBagSharedFile( fsRdWrPerm, &g.sharedFileRefNum ); UpdateErrorMessage( window, "Open For Writing", err );}void SaveDataToGrabBagSharedFile( WindowRef window ){ OSErr err; err = WriteToGrabBagSharedFile( window ); UpdateErrorMessage( window, "Save To File", err );}void DisplayDataFromGrabBagSharedFile( WindowRef window ){ OSErr err; err = ReadFromGrabBagSharedFile( window ); UpdateErrorMessage( window, "Read From File", err );}void CloseGrabBagSharedFile( WindowRef window ){ OSErr err; err = XFSClose( &g.sharedFileRefNum ); UpdateErrorMessage( window, "Close File", err );}static void UpdateErrorMessage( WindowRef window, char *errMsg, OSErr err ){ char s[1024]; ControlRef control; ControlID controlID = { 'eror', 0 }; sprintf( s, "%s\r\rOSErr = %d", errMsg, err ); GetControlByID( window, &controlID, &control ); (void) SetControlData( control, 0, kControlStaticTextTextTag, strlen(s), s ); Draw1Control( control );}static OSErr OpenGrabBagSharedFile( short permission, short *refNum ){ short foundVRefNum; long foundDirID; FSSpec spec; OSErr err; err = FindFolder( kOnAppropriateDisk, kSharedUserDataFolderType, true, &foundVRefNum, &foundDirID ); if ( err != noErr ) goto Bail; err = FSMakeFSSpec( foundVRefNum, foundDirID, "\pGrabBagSharedFile", &spec ); if ( err == fnfErr ) err = FSpCreate( &spec, 0, 0, smSystemScript ); if ( err != noErr ) goto Bail; err = XFSpOpenDF( &spec, permission, refNum ); Bail: return( err );}static OSErr ReadFromGrabBagSharedFile( WindowRef window ){ OSErr err; ControlRef control; char buffer[1024]; long count = 1024; short refNum = g.sharedFileRefNum; ControlID controlID = { 'FDta', 0 }; if ( g.sharedFileRefNum == 0 ) { err = OpenGrabBagSharedFile( fsRdPerm, &refNum ); if ( err != noErr ) goto Bail; } (void) SetFPos( refNum, fsFromStart, 0); err = FSRead( refNum, &count, buffer ); if ( (err != noErr) && (err != eofErr) ) goto Bail; if ( g.sharedFileRefNum == 0 ) FSClose( refNum ); GetControlByID( window, &controlID, &control ); err = SetControlData( control, 0, kControlStaticTextTextTag, count, buffer ); Draw1Control( control ); Bail: return( err );}static OSErr WriteToGrabBagSharedFile( WindowRef window ){ OSErr err; ControlRef control; char buffer[1024]; long count = 1024; short refNum = g.sharedFileRefNum; ControlID controlID = { 'FDta', 0 }; if ( g.sharedFileRefNum == 0 ) { err = OpenGrabBagSharedFile( fsRdWrPerm, &refNum ); if ( err != noErr ) goto Bail; } GetControlByID( window, &controlID, &control ); (void) GetControlData( control, 0, kControlStaticTextTextTag, count, buffer, &count ); (void) SetFPos( refNum, fsFromStart, 0); err = FSWrite( refNum, &count, buffer ); if ( err != noErr ) goto Bail; (void) SetEOF( refNum, count ); Bail: if ( g.sharedFileRefNum == 0 ) XFSClose( &refNum ); return( err );}OSErr XFSClose( short *refNum ){ FSSpec lockFileSpec; Str31 name; OSErr err; FCBPBRec fcbRec; fcbRec.ioRefNum = *refNum; fcbRec.ioNamePtr = name; fcbRec.ioFCBIndx = 0; fcbRec.ioVRefNum = 0; fcbRec.ioFCBParID = 0; err = PBGetFCBInfoSync( &fcbRec ); if ( err != noErr ) return( fnOpnErr ); err = FSClose( *refNum ); if ( err != noErr ) goto Bail; *refNum = 0; if ( name[0] > 26 ) name[0] = 26; // truncate the name to 31 chars PLstrcat( name, "\p.lock" ); err = FSMakeFSSpec( fcbRec.ioFCBVRefNum, fcbRec.ioFCBParID, name, &lockFileSpec ); if ( err == noErr ) // should always be there in this case err = FSpDelete( &lockFileSpec ); else if ( err == fnfErr ) err = noErr; Bail: return( err );}OSErr XFSpOpenDF( FSSpec *spec, short permission, short *refNum ){ OSErr err; if ( permission == fsRdWrPerm ) { err = WriteLockTheFile( spec ); if ( err != noErr ) goto Bail; } err = FSpOpenDF( spec, permission, refNum );Bail: return( err );}static OSErr WriteLockTheFile( FSSpec *spec ){ ProcessSerialNumber psn; ProcessInfoRec processInfo; OSErr err; FSSpec lockFileSpec = *spec; Boolean isWriteLocked = true; short refNum = 0; long count = sizeof( psn ); if ( lockFileSpec.name[0] > 26 ) lockFileSpec.name[0] = 26; // truncate the name to 31 chars PLstrcat( lockFileSpec.name, "\p.lock" ); err = FSMakeFSSpec( spec->vRefNum, spec->parID, lockFileSpec.name, &lockFileSpec ); if( err == fnfErr ) { isWriteLocked = false; } else { if ( err == noErr ) { err = FSpOpenDF( &lockFileSpec, fsRdPerm, &refNum ); if ( err != noErr ) goto Bail; err = FSRead( refNum, &count, &psn ); if ( count == sizeof(psn) ) { FSSpec sp; processInfo.processAppSpec = &sp; processInfo.processName = NULL; processInfo.processInfoLength = sizeof(ProcessInfoRec); err = GetProcessInformation( &psn, &processInfo ); if ( err != noErr ) { (void) FSClose( refNum ); refNum = 0; (void) FSpDelete( &lockFileSpec ); isWriteLocked = false; } else { err = wrPermErr; } } else { (void) FSpDelete( &lockFileSpec ); isWriteLocked = false; } } } if ( isWriteLocked == false ) { err = GetCurrentProcess( &psn ); if ( err != noErr ) goto Bail; err = FSpCreate( &lockFileSpec, 0, 0, smSystemScript ); // create the lock file if ( err != noErr ) goto Bail; err = FSpOpenDF( &lockFileSpec, fsRdWrPerm, &refNum ); if ( err == noErr ) { count = sizeof(psn); (void) FSWrite( refNum, &count, &psn ); } if ( refNum != 0 ) (void) FSClose( refNum ); return( noErr ); } Bail: if ( refNum != 0 ) (void) FSClose( refNum ); return( wrPermErr );}</pre>
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