DDLog使用注意事项

DDOSLogger控制台打印，没有使用logMessage的时间戳而是os_log_xxx执行时的时间戳，因此会和logMessage的创建时间有个时间差。如果打印时选择的是DDLogFlagError，打印将是同步执行，这个时间差会非常小。而如果是DDLogFlagError以下级别，那么这条打印将是异步执行的，这时的时间差会更大，和NSLog混用时可能会误导你。因此和NSLog混用或者场景同步打印要求比较高，建议使用DDLogFlagError同步打印日志。

- (DDLoggerName)loggerName {
    return DDLoggerNameOS;
}

- (void)logMessage:(DDLogMessage *)logMessage {
    // Skip captured log messages
    if ([logMessage->_fileName isEqualToString:@"DDASLLogCapture"]) {
        return;
    }

    if (@available(iOS 10.0, macOS 10.12, tvOS 10.0, watchOS 3.0, *)) {
        NSString * message = _logFormatter ? [_logFormatter formatLogMessage:logMessage] : logMessage->_message;
        if (message != nil) {
            const char *msg = [message UTF8String];
            __auto_type logger = [self logger];
            switch (logMessage->_flag) {
                case DDLogFlagError  :
                    os_log_error(logger, "%{public}s", msg);
                    break;
                case DDLogFlagWarning:
                case DDLogFlagInfo   :
                    os_log_info(logger, "%{public}s", msg);
                    break;
                case DDLogFlagDebug  :
                case DDLogFlagVerbose:
                default              :
                    os_log_debug(logger, "%{public}s", msg);
                    break;
            }
        }
    }
}

例子：打印时选择的是DDLogFlagDebug。

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
 completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler
{
    NSLog(@"接收到响应1:%@, 线程：%@", response.URL.lastPathComponent, [NSThread currentThread]);
    MATLogDebug(@"MAT,接收到响应:%@, 线程：%@", response, [NSThread currentThread]);
    NSLog(@"接收到响应2:%@, 线程：%@", response.URL.lastPathComponent, [NSThread currentThread]);
    
    completionHandler(NSURLSessionResponseAllow);
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
    NSURL *url = dataTask.originalRequest.URL;
    NSMutableData *dataContainer = [self dataWithURL:url];
    [dataContainer appendData:data];
    
    NSLog(@"本次接收1:%ld,线程：%@, url:%@", data.length, [NSThread currentThread], url.lastPathComponent);
    
    if (url.absoluteString == landscapeUrl) {
        sleep(10);
    }
    NSLog(@"本次接收2:%ld,总共接收:%ld,线程：%@, url:%@", data.length, dataContainer.length, [NSThread currentThread], url.lastPathComponent);
}

日志：

2023-04-04 11:05:59.463803+0800 AFNetworking_fx[3039:152895] <__NSURLSessionLocal: 0x103b48e60>
2023-04-04 11:06:00.468738+0800 AFNetworking_fx[3039:152895] 开始请求：https://tinypng.com/images/example-orig.png
2023-04-04 11:06:00.598328+0800 AFNetworking_fx[3039:154867] 接收到响应1:example-orig.png, 线程：<NSThread: 0x2824d0f40>{number = 16, name = (null)}
2023-04-04 11:06:00.599692+0800 AFNetworking_fx[3039:154867] -----1:2023-04-04 11:06:00:600---------
2023-04-04 11:06:00.600230+0800 AFNetworking_fx[3039:154867] -----2:2023-04-04 11:06:00:600---2023-04-04 11:06:00:600------
2023-04-04 11:06:00.600749+0800 AFNetworking_fx[3039:154867] 接收到响应2:example-orig.png, 线程：<NSThread: 0x2824d0f40>{number = 16, name = (null)}
2023-04-04 11:06:00.601729+0800 AFNetworking_fx[3039:154867] 本次接收1:5455,线程：<NSThread: 0x2824d0f40>{number = 16, name = (null)}, url:example-orig.png
2023-04-04 11:06:00.601922+0800 AFNetworking_fx[3039:154874] 2023-04-04 11:06:00:600 -[SystemSessionViewController URLSession:dataTask:didReceiveResponse:completionHandler:] +171 [level:Debug,module:0]
MAT,接收到响应:<NSHTTPURLResponse: 0x2831fa500> { URL: https://tinypng.com/images/example-orig.png } { Status Code: 200, Headers {

logMessage的创建时间是2023-04-04 11:06:00:600，但控制台显示的时间戳是2023-04-04 11:06:00.601922+0800。相差2ms。还以为是didReceiveData的调用跑到didReceiveResponse前面去了，原来是打印的问题。