我有一个 NSOperationQueue ,它包含 2 个 NSOperations 并设置为通过设置setMaxConcurrentOperationCount
为 1 一个接一个地执行它们。
其中一个操作是标准的非并发操作(只是一个main
方法),它同步地从 Web 检索一些数据(当然是在单独的操作线程上)。另一个操作是并发操作,因为我需要使用一些必须异步运行的代码。
问题是我发现并发操作只有在首先添加到队列时才有效。如果它发生在任何非并发操作之后,那么奇怪的是该start
方法被调用得很好,但是在该方法结束并且我已经设置我的连接来回调一个方法之后,它永远不会这样做。之后不会执行队列中的进一步操作。就好像它在 start 方法返回后挂起,并且没有调用来自任何 url 连接的回调!
如果我的并发操作首先放在队列中,那么一切正常,异步回调工作,后续操作在完成后执行。我完全不明白!
你可以在下面看到我的并发 NSOperation 的测试代码,我很确定它是可靠的。
任何帮助将不胜感激!
主线程观察:
我刚刚发现,如果并发操作首先在队列上,那么该[start]
方法将在主线程上调用。但是,如果它不是队列中的第一个(如果它在并发或非并发之后),[start]
则不会在主线程上调用该方法。这似乎很重要,因为它符合我的问题的模式。这可能是什么原因?
并发 NSOperation 代码:
@interface ConcurrentOperation : NSOperation {
BOOL executing;
BOOL finished;
}
- (void)beginOperation;
- (void)completeOperation;
@end
@implementation ConcurrentOperation
- (void)beginOperation {
@try {
// Test async request
NSURLRequest *r = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://www.google.com"]];
NSURLConnection *c = [[NSURLConnection alloc] initWithRequest:r delegate:self];
[r release];
} @catch(NSException * e) {
// Do not rethrow exceptions.
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(@"Finished loading... %@", connection);
[self completeOperation];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog(@"Finished with error... %@", error);
[self completeOperation];
}
- (void)dealloc {
[super dealloc];
}
- (id)init {
if (self = [super init]) {
// Set Flags
executing = NO;
finished = NO;
}
return self;
}
- (void)start {
// Main thread? This seems to be an important point
NSLog(@"%@ on main thread", ([NSThread isMainThread] ? @"Is" : @"Not"));
// Check for cancellation
if ([self isCancelled]) {
[self completeOperation];
return;
}
// Executing
[self willChangeValueForKey:@"isExecuting"];
executing = YES;
[self didChangeValueForKey:@"isExecuting"];
// Begin
[self beginOperation];
}
// Complete Operation and Mark as Finished
- (void)completeOperation {
BOOL oldExecuting = executing;
BOOL oldFinished = finished;
if (oldExecuting) [self willChangeValueForKey:@"isExecuting"];
if (!oldFinished) [self willChangeValueForKey:@"isFinished"];
executing = NO;
finished = YES;
if (oldExecuting) [self didChangeValueForKey:@"isExecuting"];
if (!oldFinished) [self didChangeValueForKey:@"isFinished"];
}
// Operation State
- (BOOL)isConcurrent { return YES; }
- (BOOL)isExecuting { return executing; }
- (BOOL)isFinished { return finished; }
@end
排队码
// Setup Queue
myQueue = [[NSOperationQueue alloc] init];
[myQueue setMaxConcurrentOperationCount:1];
// Non Concurrent Op
NonConcurrentOperation *op1 = [[NonConcurrentOperation alloc] init];
[myQueue addOperation:op1];
[op1 release];
// Concurrent Op
ConcurrentOperation *op2 = [[ConcurrentOperation alloc] init];
[myQueue addOperation:op2];
[op2 release];