编写`NSOutputStream`的问题.

Question

我有一个基本问题,在使用时NSOutputStream,我们是否应该等待NSStreamEventHasSpaceAvailable发送数据包,以便我们可以[NSOutputStream write]在需要时调用它,

我相信NSStream应该照顾写功能......

如果这不正确,那么请提供您对以下逻辑的看法,

=====写上NSOutputStream=================有队列添加数据包,即发送//StreamQueue.h

@interface StreamQueue : NSObject <NSCoding>
{
    NSMutableArray * data;
    NSRecursiveLock * theLock;
}

#pragma mark ?Initialization & Deallocation?
- (id)init;
- (id)initWithQueue:(CommQueue *)queue;
- (id)initWithCoder:(NSCoder *)coder;
- (void)dealloc;
- (void)encodeWithCoder:(NSCoder *)coder;

#pragma mark
#pragma mark ?Accessor Methods?
- (int)size;
- (BOOL)isEmpty;
- (id)top;
- (NSArray *)data;

#pragma mark
#pragma mark ?Modifier Methods?
- (void)enqueue:(id)object;
- (id)dequeue;
- (void)removeAll;
@end

及其实施

#import "StreamQueue.h"


@implementation StreamQueue
#pragma mark ?Initialization & Deallocation?
- (id)init
{
    if (self = [super init]) {
        data = [[NSMutableArray alloc] init];
        theLock = [[NSRecursiveLock alloc] init];
    }
    return self;
}

- (id)initWithQueue:(StreamQueue *)queue
{
    if (self = [super init]) {
        data = [[NSMutableArray alloc] initWithArray:[queue data]];
        theLock = [[NSRecursiveLock alloc] init];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)coder
{
    if (self = [super init]) {
        data = [[NSMutableArray alloc] initWithArray:[coder decodeObject]];
        theLock = [[NSRecursiveLock alloc] init];
    }
    return self;
}

- (void)dealloc
{
    [data release];
    [theLock release];
    [super dealloc];
}

- (void)encodeWithCoder:(NSCoder *)coder;
{
    [coder encodeObject:data];
}

#pragma mark
#pragma mark ?Accessor Methods?
- (int)size
{
    int size;
    [theLock lock];
    size = [data count];
    [theLock unlock];
    return size;
}

- (BOOL)isEmpty
{
    BOOL empty;
    [theLock lock];
    empty = ([data count] == 0);
    [theLock unlock];
    return empty;
}

- (id)top
{
    id object = nil;
    [theLock lock];
    if (![self isEmpty])
        object = [data objectAtIndex:0];
    [theLock unlock];
    return object;
}

- (NSArray *)data
{
    NSArray * array;
    [theLock lock];
    array = [NSArray arrayWithArray:data];
    [theLock unlock];
    return array;
}

#pragma mark
#pragma mark ?Modifier Methods?
- (void)enqueue:(id)object
{
    [theLock lock];
    [data addObject:object];
    [theLock unlock];
}

- (id)dequeue
{
    id object = [self top];
    if (object != nil) {
        [theLock lock];
        [object retain];
        [data removeObjectAtIndex:0];
        [theLock unlock];
    }
    return [object autorelease];
}

- (void)removeAll
{
    [theLock lock];
    while (![self isEmpty])
        [data removeObjectAtIndex:0];
    [theLock unlock];
}
@end

现在,当Application通过socket(NSStream)发送内容时,它应该将它添加到队列中,

-(bool)sendRawData:(const uint8_t *)data length:(int)len{

    // if still negotiating then don't send data
    assert(!networkConnected);

    NSData *pData  = [NSData dataWithBytes:(const void *)data length:len];

    // pToSendPacket is of type StreamQueue 
    [pToSendPacket enqueue:pData];

    return;
}

当我们得到这条代码时 NSHasSpaceAvailableEvent

-(void)gotSpaceAvailable{
    // is there any pending packets that to be send. 
    NSData *pData = (NSData *)[pToSendPacket dequeue];

    if(pData == nil){
        // no pending packets.. 
        return;
    }

    const uint8_t *data = (const uint8_t *)[pData bytes];
    int len = [pData length];

    int sendlength = [pOutputStream write:data maxLength:len];

    if(sendlength == -1 ){
        NSError *theError = [pOutputStream streamError];
        NSString *pString = [theError localizedDescription];
        int errorCode = [theError code];
        return ;
    }
}

我期待应用程序将继续接收事件,每当OutputStream发送数据,但我只收到一次... :(请帮助...

Answer 1

如果您不等待事件,则写入调用将阻塞,直到空间可用.通常,您希望设计代码以便异步工作,因此等待NSStreamEventHasSpaceAvailable是最佳解决方案.

至于何时收到可用空间通知,请参阅此处的文档:

如果委托收到NSStreamEventHasSpaceAvailable事件并且没有向流写入任何内容,则它不会从运行循环接收更多空间可用事件,直到NSOutputStream对象接收到更多字节.发生这种情况时,将重新启动运行循环以获取空间可用事件.如果您的实现中可能出现这种情况,则在收到NSStreamEventHasSpaceAvailable事件时,如果委托不写入流,则可以让委托设置一个标志.稍后,当您的程序有更多字节要写时,它可以检查此标志,如果设置,则直接写入输出流实例.

关于一次写入多少字节没有确切的指导.尽管可以在一个事件中将所有数据写入流中,但这取决于外部因素,例如内核的行为以及设备和套接字特性.最好的方法是使用一些合理的缓冲区大小,例如512字节,1千字节(如上例所示)或页面大小(4千字节).

因此,只要您为每个事件写入数据,就应该获得常规的NSStreamEventHasSpaceAvailable事件.