After reading a bunch of POSIX specs, I've learned that a file descriptor
is the number that refers to a file description, not the description itself.
So this patch renames FileDescriptor to FileDescription, and Process now has
FileDescription* file_description(int fd).
There are now two thread lists, one for runnable threads and one for non-
runnable threads. Thread::set_state() is responsible for moving threads
between the lists.
Each thread also has a back-pointer to the list it's currently in.
This means that kernel regions will eagerly get physical pages allocated.
It would be nice to zero-fill these on demand instead, but that would
require a bunch of MemoryManager changes.
This patch moves away from using kmalloc memory for thread kernel stacks.
This reduces pressure on kmalloc (16 KB per thread adds up fast) and
prevents kernel stack overflow from scribbling all over random unrelated
kernel memory.
Make the Socket functions take a FileDescriptor& rather than a socket role
throughout the code. Also change threads to block on a FileDescriptor,
rather than either an fd index or a Socket.
We were only destroying the main thread when a process died, leaving any
secondary threads around. They couldn't run, but because they were still
in the global thread list, strange things could happen since they had some
now-stale pointers to their old process.
Add a Thread::is_thread(void*) helper that we can use to check that the
incoming donation beneficiary is a valid thread. The O(n) here is a bit sad
and we should eventually rethink the process/thread table data structures.
We can't have multiple threads in the same process running in the kernel
at the same time, so let's have a per-process lock that threads have to
acquire on syscall entry/exit (and yield while blocked.)
The scheduler now operates on threads, rather than on processes.
Each process has a main thread, and can have any number of additional
threads. The process exits when the main thread exits.
This patch doesn't actually spawn any additional threads, it merely
does all the plumbing needed to make it possible. :^)
