Hello erlang gurus,
Currently I’ve faced with the following issue with termination of threads created in port drivers.
I’m creating a separate thread in the erlang port driver that sends terms to some erlang process.
--------------------------------------
The thread is created like this:
ErlDrvTid threadId;
if(erl_drv_thread_create(“thread name”, &threadId, threadFunc, threadData, NULL)) {
// log error & exit
}
driverData->tid = threadId;
Driver data looks like this:
struct DriverData {
ErlDrvPort port;
ErlDrvTid tid;
int isRunning;
}
--------------------------------------
Thread function looks like this
DriverData* data = (DriverData*) threadData
data. isRunning = 1;
while(data.isRunning) {
doSomething();
}
--------------------------------------
When I’d like to stop this thread from one of the driver callbacks I do something like this:
void handleInput(ErlDrvData handle, char * buf, ErlDrvSizeT len) {
DriverData* data = (DriverData*) handle;
int command = parseBuf(buf, len);
if (command == STOP) {
data.isRunning = 0;
if(erl_drv_thread_join(data->tid, NULL)) { // here is the place where EDEADLK happens
// report error
}
} else {
…
}
}
From time to time erl_drv_thread_join returns error EDEADLK=35, i.e. the current thread (scheduler thread) tries to join itself.
According to the documentation “A Thread identifier may be reused very quickly after a thread has terminated. Therefore, if a thread corresponding to one of the involved thread identifiers has terminated since the thread identifier was saved, the result of erl_drv_equal_tids() might not give the expected result.”
I suppose that thread terminates earlier then erl_drv_thread_join call happens, so ErlDrvTid is already reused.
So the question is how to use erl_drv_thread_join properly and how to guarantee that the saved ErlDrvTid value points to the same data that was returned from erl_drv_thread_create?
Best Regards,
Sergey
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