从串口读取时,我无法使用Grand Central Dispatch Source事件.
我将dispatch_source_create与DISPATCH_SOURCE_TYPE_READ一起使用,以便当从与串行端口关联的fileDescriptor中读取数据时,操作系统将运行我的代码块.这是我的代码
- (void) receiveThread
{
globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
readSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ,[self fileDescriptor],globalQueue);
dispatch_source_set_event_handler(readSource,^{
char buffer[512];
NSString *bar;
ssize_t numBytes;
int expected;
expected = dispatch_source_get_data(readSource);
printf("expected:%d\n",expected);
do {
numBytes = read([self fileDescriptor],buffer,512);
buffer[numBytes] = '\x000'; //make sure that the string is terminated.
printf("bytes:%ld\n",numBytes);
if (numBytes != -1)
{
bar = [NSString stringWithCString:&buffer];
//printf("bytes:%ld\n",numBytes);
NSLog(@"String:%@\n",bar);
[[NSNotificationCenter defaultCenter] postNotificationName:EISerialTextDidArrive object:bar];
}
} while (numBytes > 0);
});
dispatch_resume(readSource);
}
当程序运行时,第一次将串行数据发送到端口时调用该块.然后我在控制台中收到一条消息
[Switching to process 11969 thread 0x6603]
当更多字符被发送到串行端口时,不会调用代码块.我仍然可以从串口发送字符,我可以确认正在发送字符,但块不会再次运行.
从Web上的文档和示例我希望只要串行缓冲区中有字符就可以重复调用块.
解决方法
@KazukiSakamoto指出文件描述符应该设置O_NONBLOCK是正确的.我发现了其他一些可能让你感到困扰的问题：当你应该使用缓冲区时,你正在使用& buffer.此外,您有一个512字节的缓冲区,然后您读取最多512个字节并将下一个设置为0(用于空终止).如果您实际读取了512个字节,则会导致缓冲区溢出.此外,看起来readSource是一个iVar,你在块中引用self.这可能会创建一个保留周期,应该避免.
无论如何,我编写了最简单的小应用程序,然后缩短了我的串口的引脚2和3,所以写出的任何内容都会被回显,然后在我的应用程序中连接一个按钮来发送一些数据.像魅力一样工作！这是代码：
@implementation SOAppDelegate
{
int fd;
dispatch_source_t readSrc;
}
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
fd = open("/dev/mySerialPort",O_RDWR | O_NONBLOCK);
__block dispatch_source_t blockReadSrc = readSrc = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ,fd,dispatch_get_main_queue());
dispatch_source_set_event_handler(readSrc,^{
NSLog(@"expected: %lu\n",dispatch_source_get_data(blockReadSrc));
ssize_t numBytes;
do {
char buffer[513];
numBytes = read((int)dispatch_source_get_handle(blockReadSrc),512);
buffer[numBytes] = '\x000'; //make sure that the string is terminated.
NSLog(@"numBytes: %ld\n",numBytes);
if (numBytes != -1)
{
NSLog(@"String:%@\n",[NSString stringWithUTF8String: buffer]);
}
} while (numBytes > 0);
});
dispatch_resume(readSrc);
}
- (IBAction)sendData: (id)sender
{
write(fd,"foobar",6);
}
- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender
{
if (fd > 0) close(fd); fd = 0;
if (readSrc) dispatch_release(readSrc); readSrc = nil;
return NSTerminateNow;
}
@end