Hi,
I have a problem with inter-thread communications with NSMachPort/
NSPortMessage - it works one way after initially working both ways..
The application has a main parent thread that spawns a child thread.
The child thread runs inside an object instance.
The parent passes it's NSMachPort instance through the NSThread
detachNewSelector to the child. The parent runs a loop and drives
it's RunLoop.
The child once spawned creates it's own NSMachPort instance and then
packages it up and sends it to the parent (which the parent receives
correctly). This is the classic Apple documented 'checkin'. It then
enters the classic while(1) { RunLoop ... } to drive the runloop.
Assumption #1 - as the threads are both running "currentRunLoop" then
I'm assuming that each thread has it's own RunLoop instance? I
understand that the RunLoop is thread unsafe.
The parent can issue as many messages as it likes to the child
process. Each message gets to the child thread without a problem -
each and every time.
Now comes the interesting bit.
The child uses a single method for all it's send calls back to the
parent thread - even the checkin uses it - where it calls
[NSPortMessage sendMessage: ...]. The observed results are that the
initial checkin message gets to the parent handlePortMessage: whereas
subsequent calls don't show any errors but the message does not arrive
at handlePortMessage on the parent. They just vanish. The child and
parent threads continue as if nothing has happened. The parent can
still issue messages to the child..
I've checked with gdb and the ports are correct at each call. I notice
there's three threads (the thread that's not mine shows as a posix
thread that runs __CFSocketManager and just sits at select
$DARWIN_EXTSN). This may be handling the streams that my child thread
manages (I assume).
Activity monitor sample shows the parent 100% in it's loop. The child
100% sat at mach_msg_trap which I see from the Apple opensource is the
send/receive for messages in the mach kernel.
Has anyone had this occur before? Is it a dead/live lock in the OS due
to threads using each others ports or is it there's no messages being
sent?
I'm a complete beginner to OSX/Cocoa but not threading.
Cheers,
Nick.
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