I've always longed for a good, fast way to relay information between threads. So, I built one!

What's a message? It's anything you want it to be: a built-in data type, a character string, a function pointer, or a complicated data structure. The queue won't copy or move your structure, so internal pointers remain intact. A message is anything your application wants to send between threads.

The library uses a lock-free allocator to allocate memory for messages. Then, your application can construct whatever it needs to send in-place. When you write the message to the queue, it's added to a lock-free structure similar to the one used to allocate memory.

• It's fast. Crazy fast. My three-year-old laptop can push around 6,500,000 messages per second between threads, including the overhead of allocating the messages.

• It's easy. There are only 8 functions to learn, and you probably only need 6 of them. Really, there are only 3 concepts to worry about:

  • initialization/teardown,
  • allocation/deallocation, and
  • writing/reading.

  If you're a C programmer, you've dealt with all of these already.

• It's new and so not widely tested. In fact, it's only been tested at all on two x86_64 machines, running Mac OS X and Linux.
• It may be overly tuned to my Core 2 Duo. Performance is tricky and often very hardware dependent. Hopefully wider exposure will help this work well on a wider variety of hardware.
• I have no clue how well it scales past two CPUs. Anyone want to try it on a bigger, beefier machine?
• You have to know how big the largest message you want to send on a given queue is in advance, and you have to decide on a maximum depth the queue can reach.

First, set up a message queue somewhere:

struct message_queue queue;

Before using it, you have to initialize it:

message_queue_init(&queue, 512, 128); /* The biggest message we'll send
                                       * with this queue is 512 bytes, and
                                       * the queue can only be 128
                                       * messages deep */

To send a message:

struct my_message *message = message_queue_message_alloc_blocking(&queue);
/* Construct the message here */
message_queue_write(&queue, message);

Or, if you'd rather discard your message if there's no free memory in the queue:

struct my_message *message = message_queue_message_alloc(&queue);
if(message) {
    /* Construct the message here */
    message_queue_write(&queue, message);
}

To read a message:

/* Blocks until a message is available */
struct my_message *message = message_queue_read(&queue);
/* Do something with the message here */
message_queue_message_free(&queue, message);

If you'd rather not block to wait for a new message:

/* Returns NULL if no message is available */
struct my_message *message = message_queue_tryread(&queue);
if(message) {
    /* Do something with the message here */
    message_queue_message_free(&queue, message);
}

Whenever you're done with the queue (and no other threads are accessing it anymore):

message_queue_destroy(&queue);

So give it a shot and let me know what you think!