README.md

Spawn

In this demo we are going to show the mechanism that a thread can use to spawn other threads.

To illustrate this demo, we need to introduce the following:

• add_named_thread (in src/user/thread.c)
• thread_name (in src/user/thread.c)

add_named_thread

add_named_thread uses the name and worker we provided to create a thread and initializes all its arguments to 0.

If the creation succeeds, the function returns the ID of the thread. If creation fails, it returns INVALID_THREAD.

After the creation, the new thread waits until it is yielded to.

thread_name

In Badger Kernel, we store the name of a thread in a Thread structure.

When we call this function for the current thread it will copy the name from user_thread_info into the location pointed to by name. If we're asking about another thread then it will use the get_thread_property syscall with TPROP_NAME to have the kernel copy it into name.

Walkthrough

We start from the setup() function. The setup() function is just a starting point for thread 0 to run, so we directly jump into spawner() function.

When we enter the function, it first sets the thread name to spawner, then creates 3 threads called Morgoth, Sauron and Khamul. After each thread has been created, we send a message to it. These messages indicate how many turns it should wait to log its greeting.

The table below shows the relation between the messages we sent and the destination threads:

0  ->  Morgoth
1  ->  Sauron
2  ->  Khamul

After spawner finishes thread creating and message sending, it calls thread_join() to wait for all threads except itself and yields.

Since the message number that each thread got is 0, 1 and 2, we will print out the greetings of Morgoth, Sauron and Khamul respectively after yielding that many times.

These threads end after they print out the log, so the spawner finishes waiting and thus ends the demo.