Assume this over-simplified @protocol I'm using for my XPC-service:
@protocol MyMinimalProtocol <NSObject>
- (void)getStatusWithReply:(void (^ _Nullable)(NSDictionary * _Nonnull))reply;
@end
The Client side would then
NSXPCConnection *connection = [[NSXPCConnection alloc] initWithMachServiceName:myServiceLabel options:NSXPCConnectionPrivileged];
connection.remoteObjectInterface = [NSXPCInterface interfaceWithProtocol:@protocol(MyMinimalProtocol)];
connection.interruptionHandler = ^{ NSLog(@"XPC: connection - interrupted"); };
connection.invalidationHandler = ^{ NSLog(@"XPC: connection - invalidated"); };
[connection resume];
[connection.remoteObjectProxy getStatusWithReply:^(NSDictionary * response) {
NSLog(@"XPC service status received - %@", response);
}];
So far - so good. My XPC service receives the asynchronous call, schedules it's "status gathering operation" on internal background queue, and returns. Later - when information is available, my XPC service executes the reply-block then, on the remote calling side - I see the log line with the status, as expected.
BUT!!!
If I add another different code-block argument to the method e.g.
@protocol MyMinimalProtocol <NSObject>
- (void)getStatusWithReply:(void (^ _Nullable)(NSDictionary * _Nonnull))reply andFailureBlock:(void (^ _Nullable)(NSError * _Nonnull))failureBlock;
@end
Then all hell breaks loose. Both XPC service and the client crash with hilarious crash reasons I can't decipher.
Here's "Client side" caller crash (excerpt - forgive the methods are NOT the simplified ones above)
while on the "XPC Service" side, crashes like these:
I wonder if there's something inherently wrong with having two code-block arguments for an XPC remote method?
Another issue. The client XPC calls are asynchronous. They return immediately. The XPC service implementing the remote-call also returns immediately - and it executes the "reply block" far (a minute!) later, on another queue.
However, if the XPC service attempts to execute the code-block MORE THAN ONCE, then the client-side code-block is only called ONCE. rest of the executions look benign in the XPC-service side - but never happen on the calling (client) side.
Any idea why? can this be overcome?
Any thoughts/ideas/references to documentation will be greatly appreciated. I couldn't find any good source on this.
Thanks.
