Use a Queue to Communicate Between Threads in D - multithreading

Question

It is easy enough in D to create a Queue type using the std.container.dlist.
I would like to have multiple threads but have them communicate with a queue, not with message passing (https://tour.dlang.org/tour/en/multithreading/message-passing). As I understand it the messages are designed to always receive data at particular points in the code; the receiving thread will block until the expected data is received.
(EDIT: I was informed about receiveTimeout but having a no timeout and just a check is really more appropriate in this case (maybe a timeout of 0?). Also I am not sure what the message API will do if multiple messages are sent before any any are received. I will have to play with that.)
void main() {
spawn(&worker, thisTid);
// This line will block until the expected message is received.
receive (
(string message) {
writeln("Received the message: ", text);
},
)
}
What I am needing is to merely receive data if there is some. Something like this:
void main() {
Queue!string queue// custom `Queue` type based on DList
spawn(&worker, queue);
while (true) {
// Go through any messages (while consuming `queue`)
for (string message; queue) {
writeln("Received a message: ", text);
}
// Do other stuff
}
}
I have tried using shared variables (https://tour.dlang.org/tour/en/multithreading/synchronization-sharing) but DMD is complaining that "Aliases to mutable thread-local data not allowed." or some other errors, depending.
How would this be done in D? Or, is there a way to use messages to do this kind of communication?

Answer 1

This doesn't answer the specific question but ti does clear up what I think is a misunderstanding of the message passing api...
just call receiveTimeout instead of plain receive
http://dpldocs.info/experimental-docs/std.concurrency.receiveTimeout.html

Answer 2

I use this:
shared class Queue(T) {
private T[] queue;
synchronized void opOpAssign(string op)(T object) if(op == "~") {
queue ~= object;
}
synchronized size_t length(){
return queue.length;
}
synchronized T pop(){
assert(queue.length, "Please check queue length, is 0");
auto first = queue[0];
queue = queue[1..$];
return first;
}
synchronized shared(T[]) consume(){
auto copy = queue;
queue = [];
return copy;
}
}

Answer 3

I have gotten the answer I need.
Simply put, use core.thread rather than std.concurrency. std.concurrency manages messages for you and does not allow you to manage it yourself. core.thread is what std.concurrency uses internally.
The longer answer, here is how I fully implemented it.
I have created a Queue type that is based on an Singly Linked List but maintains a pointer of the last element. The Queue also uses standard component inputRange and outputRange (or at least I think it does) per Walter Brights vision (https://www.youtube.com/watch?v=cQkBOCo8UrE).
The Queue is also built to allow one thread to write and another to read with very little mutexing internally so it should be fast.
The Queue I shared here https://pastebin.com/ddyPpLrp
A simple implementation to have a second thread read input:
Queue!string inputQueue = new Queue!string;
ThreadInput threadInput = new ThreadInput(inputQueue);
threadInput.start;
while (true) {
foreach (string value; inputQueue) {
writeln(value);
}
}
ThreadInput being defined as thus:
class ThreadInput : Thread {
private Queue!string queue;
this(Queue!string queue) {
super(&run);
this.queue = queue;
}
private void run() {
while (true) {
queue.put(readln);
}
}
}
The code https://pastebin.com/w5jwRVrL
The Queue again https://pastebin.com/ddyPpLrp