SUGlobalUpdateLock.h

//
//  SUGlobalUpdateLock.h
//  Sparkle
//
//  Created by Bibhas Acharya on 7/12/20.
//  Copyright © 2020 Sparkle Project. All rights reserved.
//

#ifndef SUGLOBALUPDATELOCK_H
#define SUGLOBALUPDATELOCK_H

#import <Foundation/Foundation.h>

@interface SUGlobalUpdateLock : NSObject
+ (SUGlobalUpdateLock *)sharedLock;
- (BOOL)tryLock;
- (void)unlock;
@end

#endif

SUGlobalUpdateLock.m

//
//  SUGlobalUpdateLock.m
//  Sparkle
//
//  Created by Bibhas Acharya on 7/12/20.
//  Copyright © 2020 Sparkle Project. All rights reserved.
//

#import "SUGlobalUpdateLock.h"

@implementation SUGlobalUpdateLock

+ (SUGlobalUpdateLock *)sharedLock
{
    static dispatch_once_t once;
    static SUGlobalUpdateLock *sharedInstance = nil;
    dispatch_once(&once, ^{
        sharedInstance = [self new];
    });
    return sharedInstance;
}

- (NSString *)fileLockPath
{
    // /var/run/$hostBundleId.Sparkle.pid
    NSString *identifier = [[NSBundle mainBundle] bundleIdentifier];
    if (identifier == nil) {
        // If there's no bundle identifier, use the executable path
        identifier = [[[NSBundle mainBundle] executablePath] stringByReplacingOccurrencesOfString:@"/" withString:@"."];
    }
    return [NSString stringWithFormat:@"/var/run/%@.Sparkle.pid", identifier];
}

- (BOOL)tryLock
{
    NSString *fileLockPath = [self fileLockPath];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager isReadableFileAtPath:fileLockPath]) {
        return NO;
    }
    if ([fileManager fileExistsAtPath:fileLockPath]) {
        return NO;
    }
    if (open(fileLockPath.UTF8String, O_CREAT|O_EXCL, S_IRUSR|S_IWUSR) < 0) {
        printf("Couldn't acquire global lock. (err = %s)", strerror(errno));
        return NO;
    }
    return YES;
}

- (void)unlock
{
    NSString *fileLockPath = [self fileLockPath];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager isReadableFileAtPath:fileLockPath]) {
        return;
    }
    if ([fileManager fileExistsAtPath:fileLockPath]) {
        return;
    }
    NSError *error = nil;
    [fileManager removeItemAtPath:fileLockPath error:&error];
    if (error != nil) {
        printf("Unable to unlock!");
    }
}

@end