解决NSDistributedLock进程互斥锁的死锁问题(二)

#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#define	O_SHLOCK	0x0010		/* open with shared file lock */
#define	O_EXLOCK	0x0020		/* open with exclusive file lock */

open(filepath, O_CREAT|O_EXLOCK,0666);

@interface QMDistributedLock : NSObject<NSLocking>
{
    NSString *filePath;
    int fileID;
}

- (instancetype)initWithPath:(NSString *)path;

@end

@implementation QMDistributedLock

- (instancetype)initWithPath:(NSString *)path
{
    self = [super init];
    if (self)
    {
        filePath = [path copy];
        if (!filePath)
            return nil;
        
        NSFileManager *fileMgr = [NSFileManager defaultManager];
        NSString *parentPath = [filePath stringByDeletingLastPathComponent];
        
        //父目录不存在
        if (![fileMgr fileExistsAtPath:parentPath])
            return nil;
        
        //父目录不可写
        if (![fileMgr isWritableFileAtPath:parentPath])
            return nil;
        
        //已经存在该名字的目录
        BOOL isDirectory = NO;
        if ([fileMgr fileExistsAtPath:filePath isDirectory:&isDirectory] && isDirectory)
        {
            if (![fileMgr removeItemAtPath:filePath error:NULL])
                return nil;
        }
    }
    return self;
}

- (void)lock
{
    fileID = open([filePath fileSystemRepresentation], O_CREAT|O_EXLOCK,0666);
}

- (void)unlock
{
    close(fileID);
}