static tid_t allocate_tid (void);
/* Initializes the threading system by transforming the code
- that's currently running into a thread. Note that this is
- possible only because the loader was careful to put the bottom
- of the stack at a page boundary; it won't work in general.
- Also initializes the run queue.
+ that's currently running into a thread. This can't work in
+ general and it is possible in this case only because loader.S
+ was careful to put the bottom of the stack at a page boundary.
+
+ Also initializes the run queue and the tid lock.
After calling this function, be sure to initialize the page
allocator before trying to create any threads with
return tid;
}
-/* Transitions a blocked thread T from its current state to the
- ready-to-run state. This is an error if T is not blocked.
- (Use thread_yield() to make the running thread ready.) */
+/* Puts the current thread to sleep. It will not be scheduled
+ again until awoken by thread_unblock().
+
+ This function must be called with interrupts turned off. It
+ is usually a better idea to use one of the synchronization
+ primitives in synch.h. */
+void
+thread_block (void)
+{
+ ASSERT (!intr_context ());
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ thread_current ()->status = THREAD_BLOCKED;
+ schedule ();
+}
+
+/* Transitions a blocked thread T to the ready-to-run state.
+ This is an error if T is not blocked. (Use thread_yield() to
+ make the running thread ready.) */
void
thread_unblock (struct thread *t)
{
schedule ();
intr_set_level (old_level);
}
-
-/* Puts the current thread to sleep. It will not be scheduled
- again until awoken by thread_unblock().
-
- This function must be called with interrupts turned off. It
- is usually a better idea to use one of the synchronization
- primitives in synch.h. */
-void
-thread_block (void)
-{
- ASSERT (!intr_context ());
- ASSERT (intr_get_level () == INTR_OFF);
-
- thread_current ()->status = THREAD_BLOCKED;
- schedule ();
-}
\f
/* Idle thread. Executes when no other thread is ready to run. */
static void
the first time a thread is scheduled it is called by
switch_entry() (see switch.S).
+ It's not safe to call printf() until the thread switch is
+ complete. In practice that means that printf()s should be
+ added at the end of the function.
+
After this function and its caller returns, the thread switch
is complete. */
void
/* Schedules a new process. At entry, interrupts must be off and
the running process's state must have been changed from
running to some other state. This function finds another
- thread to run and switches to it. */
+ thread to run and switches to it.
+
+ It's not safe to call printf() until schedule_tail() has
+ completed. */
static void
schedule (void)
{