#include "thread.h"
#include <stddef.h>
-#include "debug.h"
#include "interrupt.h"
#include "intr-stubs.h"
-#include "lib.h"
#include "mmu.h"
#include "palloc.h"
-#include "random.h"
#include "switch.h"
+#include "lib/debug.h"
+#include "lib/lib.h"
+#include "lib/random.h"
+#ifdef USERPROG
+#include "userprog/gdt.h"
+#endif
-uint32_t thread_stack_ofs = offsetof (struct thread, stack);
+/* Value for struct thread's `magic' member.
+ Used to detect stack overflow. See the big comment at the top
+ of thread.h for details. */
+#define THREAD_MAGIC 0x1234abcdu
+/* List of processes in THREAD_READY state, that is, processes
+ that are ready to run but not actually running. */
static struct list run_queue;
-static struct thread *idle_thread;
-static void
-idle (void *aux UNUSED)
-{
- for (;;)
- {
- /* Wait for an interrupt. */
- asm ("hlt");
+/* Idle thread. */
+static struct thread *idle_thread; /* Thread. */
+static void idle (void *aux UNUSED); /* Thread function. */
- /* Let someone else run. */
- intr_disable ();
- thread_sleep ();
- intr_enable ();
- }
-}
-
-void
-thread_init (void)
-{
- list_init (&run_queue);
- idle_thread = thread_create ("idle", idle, NULL);
-}
-
-struct thread_root_frame
+/* Stack frame for kernel_thread(). */
+struct kernel_thread_frame
{
void *eip; /* Return address. */
- void (*function) (void *); /* Function to call. */
+ thread_func *function; /* Function to call. */
void *aux; /* Auxiliary data for function. */
};
-static void
-thread_root (void (*function) (void *aux), void *aux)
-{
- ASSERT (function != NULL);
+static void kernel_thread (thread_func *, void *aux);
- intr_enable ();
- function (aux);
- thread_exit ();
-}
+static struct thread *running_thread (void);
+static struct thread *next_thread_to_run (void);
+static struct thread *new_thread (const char *name);
+static void init_thread (struct thread *, const char *name);
+static bool is_thread (struct thread *);
+static void *alloc_frame (struct thread *, size_t size);
+static void destroy_thread (struct thread *);
+static void schedule (void);
+void schedule_tail (struct thread *prev);
-static struct thread *
-new_thread (const char *name)
+/* 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.
+
+ After calling this function, be sure to initialize the page
+ allocator before trying to create any threads with
+ thread_create(). */
+void
+thread_init (void)
{
struct thread *t;
-
- ASSERT (name != NULL);
- t = palloc_get (PAL_ZERO);
- if (t != NULL)
- {
- strlcpy (t->name, name, sizeof t->name);
- t->stack = (uint8_t *) t + PGSIZE;
- t->status = THREAD_BLOCKED;
- }
-
- return t;
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ /* Set up a thread structure for the running thread. */
+ t = running_thread ();
+ init_thread (t, "main");
+ t->status = THREAD_RUNNING;
+
+ /* Initialize run queue. */
+ list_init (&run_queue);
}
-static void *
-alloc_frame (struct thread *t, size_t size)
+/* Starts preemptive thread scheduling by enabling interrupts.
+ Also creates the idle thread. */
+void
+thread_start (void)
{
- ASSERT (size % sizeof (uint32_t) == 0);
+ /* Create idle thread. */
+ idle_thread = thread_create ("idle", idle, NULL);
+ idle_thread->status = THREAD_BLOCKED;
- t->stack -= size;
- return t->stack;
+ /* Enable interrupts. */
+ intr_enable ();
}
+/* Creates a new kernel thread named NAME, which executes
+ FUNCTION passing AUX as the argument, and adds it to the ready
+ queue. If thread_start() has been called, then the new thread
+ may be scheduled before thread_create() returns. Use a
+ semaphore or some other form of synchronization if you need to
+ ensure ordering. */
struct thread *
-thread_create (const char *name, void (*function) (void *aux), void *aux)
+thread_create (const char *name, thread_func *function, void *aux)
{
struct thread *t;
- struct thread_root_frame *rf;
+ struct kernel_thread_frame *kf;
struct switch_entry_frame *ef;
struct switch_threads_frame *sf;
t = new_thread (name);
- /* Stack frame for thread_root(). */
- rf = alloc_frame (t, sizeof *rf);
- rf->eip = NULL;
- rf->function = function;
- rf->aux = aux;
+ /* Stack frame for kernel_thread(). */
+ kf = alloc_frame (t, sizeof *kf);
+ kf->eip = NULL;
+ kf->function = function;
+ kf->aux = aux;
/* Stack frame for switch_entry(). */
ef = alloc_frame (t, sizeof *ef);
- ef->eip = (void (*) (void)) thread_root;
+ ef->eip = (void (*) (void)) kernel_thread;
- /* Stack frame for thread_switch(). */
+ /* Stack frame for switch_threads(). */
sf = alloc_frame (t, sizeof *sf);
sf->eip = switch_entry;
/* Add to run queue. */
- thread_ready (t);
+ thread_unblock (t);
return t;
}
-struct thread *
-thread_current (void)
-{
- uint32_t *esp;
- asm ("movl %%esp, %0\n" : "=g" (esp));
- return pg_round_down (esp);
-}
-
#ifdef USERPROG
+/* Starts a new thread running a user program loaded from
+ FILENAME, and adds it to the ready queue. If thread_start()
+ has been called, then new thread may be scheduled before
+ thread_execute() returns.*/
bool
thread_execute (const char *filename)
{
if (t == NULL)
return false;
- if (!addrspace_load (&t->addrspace, filename, &start))
- panic ("%s: program load failed", filename);
+ if (!addrspace_load (t, filename, &start))
+ PANIC ("%s: program load failed", filename);
/* Interrupt frame. */
if_ = alloc_frame (t, sizeof *if_);
if_->ds = SEL_UDSEG;
if_->eip = start;
if_->cs = SEL_UCSEG;
- if_->eflags = FLAG_IF | 2;
+ if_->eflags = FLAG_IF | FLAG_MBS;
if_->esp = PHYS_BASE;
if_->ss = SEL_UDSEG;
ef = alloc_frame (t, sizeof *ef);
ef->eip = intr_exit;
- /* Stack frame for thread_switch(). */
+ /* Stack frame for switch_threads(). */
sf = alloc_frame (t, sizeof *sf);
sf->eip = switch_entry;
/* Add to run queue. */
- thread_ready (t);
+ thread_unblock (t);
return true;
}
#endif
+/* Transitions a blocked thread T from its current state to the
+ ready-to-run state. If T is not blocked, there is no effect.
+ (Use thread_yield() to make the running thread ready.) */
void
-thread_ready (struct thread *t)
+thread_unblock (struct thread *t)
{
- if (t->status != THREAD_READY)
+ enum intr_level old_level;
+
+ ASSERT (is_thread (t));
+
+ old_level = intr_disable ();
+ if (t->status == THREAD_BLOCKED)
{
- list_push_back (&run_queue, &t->rq_elem);
+ list_push_back (&run_queue, &t->elem);
t->status = THREAD_READY;
}
+ intr_set_level (old_level);
}
-static struct thread *
-find_next_to_run (void)
+/* Returns the name of thread T. */
+const char *
+thread_name (struct thread *t)
{
- if (list_empty (&run_queue))
- return NULL;
- else
- return list_entry (list_pop_front (&run_queue), struct thread, rq_elem);
+ ASSERT (is_thread (t));
+ return t->name;
}
-void
-thread_destroy (struct thread *t)
+/* Returns the running thread.
+ This is running_thread() plus a couple of sanity checks.
+ See the big comment at the top of thread.h for details. */
+struct thread *
+thread_current (void)
{
- ASSERT (t->status == THREAD_DYING);
- ASSERT (t != thread_current ());
+ struct thread *t = running_thread ();
+
+ /* Make sure T is really a thread.
+ If either of these assertions fire, then your thread may
+ have overflowed its stack. Each thread has less than 4 kB
+ of stack, so a few big automatic arrays or moderate
+ recursion can cause stack overflow. */
+ ASSERT (is_thread (t));
+ ASSERT (t->status == THREAD_RUNNING);
- palloc_free (t);
+ return t;
}
-void schedule_tail (struct thread *prev);
+/* Deschedules the current thread and destroys it. Never
+ returns to the caller. */
+void
+thread_exit (void)
+{
+ ASSERT (!intr_context ());
+
+ /* Just set our status to dying and schedule another process.
+ We will be destroyed during the call to schedule_tail(). */
+ intr_disable ();
+ thread_current ()->status = THREAD_DYING;
+ schedule ();
+ NOT_REACHED ();
+}
+/* Yields the CPU. The current thread is not put to sleep and
+ may be scheduled again immediately at the scheduler's whim. */
void
-schedule_tail (struct thread *prev)
+thread_yield (void)
{
-#ifdef USERPROG
struct thread *cur = thread_current ();
-#endif
+ enum intr_level old_level;
+
+ ASSERT (!intr_context ());
- ASSERT (intr_get_level () == IF_OFF);
+ old_level = intr_disable ();
+ list_push_back (&run_queue, &cur->elem);
+ cur->status = THREAD_READY;
+ schedule ();
+ intr_set_level (old_level);
+}
-#ifdef USERPROG
- addrspace_activate (&cur->addrspace);
-#endif
+/* Puts the current thread to sleep. It will not be scheduled
+ again until awoken by thread_unblock().
- if (prev != NULL && prev->status == THREAD_DYING)
- thread_destroy (prev);
-}
+ 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
-thread_schedule (void)
+idle (void *aux UNUSED)
{
- struct thread *cur, *next, *prev;
-
- ASSERT (intr_get_level () == IF_OFF);
+ for (;;)
+ {
+ /* Wait for an interrupt. */
+ DEBUG (idle, "idle");
+ asm ("hlt");
- cur = thread_current ();
- ASSERT (cur->status != THREAD_RUNNING);
+ /* Let someone else run. */
+ intr_disable ();
+ thread_block ();
+ intr_enable ();
+ }
+}
- next = find_next_to_run ();
- if (next == NULL)
- next = idle_thread;
+/* Function used as the basis for a kernel thread. */
+static void
+kernel_thread (thread_func *function, void *aux)
+{
+ ASSERT (function != NULL);
- next->status = THREAD_RUNNING;
- if (cur != next)
- {
- prev = switch_threads (cur, next);
+ intr_enable (); /* The scheduler runs with interrupts off. */
+ function (aux); /* Execute the thread function. */
+ thread_exit (); /* If function() returns, kill the thread. */
+}
+\f
+/* Returns the running thread. */
+struct thread *
+running_thread (void)
+{
+ uint32_t *esp;
- /* Prevent GCC from reordering anything around the thread
- switch. */
- asm volatile ("" : : : "memory");
+ /* Copy the CPU's stack pointer into `esp', and then round that
+ down to the start of a page. Because `struct thread' is
+ always at the beginning of a page and the stack pointer is
+ somewhere in the middle, this locates the curent thread. */
+ asm ("movl %%esp, %0\n" : "=g" (esp));
+ return pg_round_down (esp);
+}
- schedule_tail (prev);
- }
+/* Returns true if T appears to point to a valid thread. */
+static bool
+is_thread (struct thread *t)
+{
+ return t != NULL && t->magic == THREAD_MAGIC;
}
-void
-thread_yield (void)
+/* Creates a new thread named NAME and initializes its fields.
+ Returns the new thread if successful or a null pointer on
+ failure. */
+static struct thread *
+new_thread (const char *name)
{
- enum if_level old_level;
+ struct thread *t;
+
+ ASSERT (name != NULL);
- ASSERT (!intr_context ());
+ t = palloc_get (PAL_ZERO);
+ if (t != NULL)
+ init_thread (t, name);
- old_level = intr_disable ();
- thread_ready (thread_current ());
- thread_schedule ();
- intr_set_level (old_level);
+ return t;
}
-void
-thread_start (struct thread *t)
+/* Initializes T as a new, blocked thread named NAME. */
+static void
+init_thread (struct thread *t, const char *name)
{
- ASSERT (intr_get_level () == IF_OFF);
-
- if (t->status == THREAD_READY)
- list_remove (&t->rq_elem);
- t->status = THREAD_RUNNING;
- switch_threads (NULL, t);
- NOT_REACHED ();
+ memset (t, 0, sizeof *t);
+ strlcpy (t->name, name, sizeof t->name);
+ t->stack = (uint8_t *) t + PGSIZE;
+ t->status = THREAD_BLOCKED;
+ t->magic = THREAD_MAGIC;
}
-void
-thread_exit (void)
+/* Allocates a SIZE-byte frame at the top of thread T's stack and
+ returns a pointer to the frame's base. */
+static void *
+alloc_frame (struct thread *t, size_t size)
{
- ASSERT (!intr_context ());
+ /* Stack data is always allocated in word-size units. */
+ ASSERT (is_thread (t));
+ ASSERT (size % sizeof (uint32_t) == 0);
- intr_disable ();
- thread_current ()->status = THREAD_DYING;
- thread_schedule ();
- NOT_REACHED ();
+ t->stack -= size;
+ return t->stack;
}
-void
-thread_sleep (void)
+/* Chooses and returns the next thread to be scheduled. Should
+ return a thread from the run queue, unless the run queue is
+ empty. (If the running thread can continue running, then it
+ will be in the run queue.) If the run queue is empty, return
+ idle_thread. */
+static struct thread *
+next_thread_to_run (void)
{
- ASSERT (!intr_context ());
- ASSERT (intr_get_level () == IF_OFF);
-
- thread_current ()->status = THREAD_BLOCKED;
- thread_schedule ();
+ if (list_empty (&run_queue))
+ return idle_thread;
+ else
+ return list_entry (list_pop_front (&run_queue), struct thread, elem);
}
+/* Destroys T, which must be in the dying state and must not be
+ the running thread. */
static void
-tfunc (void *aux UNUSED)
+destroy_thread (struct thread *t)
{
- for (;;)
- {
- size_t count, i;
- if (random_ulong () % 5 == 0)
- {
- printk ("%s exiting\n", thread_current ()->name);
- break;
- }
- count = random_ulong () % 25 * 10000;
- printk ("%s waiting %zu: ", thread_current ()->name, count);
- for (i = 0; i < count; i++);
- printk ("%s\n", thread_current ()->name);
- }
+ ASSERT (is_thread (t));
+ ASSERT (t->status == THREAD_DYING);
+ ASSERT (t != thread_current ());
+
+#ifdef USERPROG
+ addrspace_destroy (t);
+#endif
+ palloc_free (t);
}
+/* Completes a thread switch by activating the new thread's page
+ tables, and, if the previous thread is dying, destroying it.
+
+ At this function's invocation, we just switched from thread
+ PREV, the new thread is already running, and interrupts are
+ still disabled. This function is normally invoked by
+ thread_schedule() as its final action before returning, but
+ the first time a thread is scheduled it is called by
+ switch_entry() (see switch.S).
+
+ After this function and its caller returns, the thread switch
+ is complete. */
void
-thread_self_test (void)
+schedule_tail (struct thread *prev)
{
- struct thread *t;
- int i;
-
- for (i = 0; i < 4; i++)
- {
- char name[2];
- name[0] = 'a' + i;
- name[1] = 0;
- t = thread_create (name, tfunc, NULL);
- }
- thread_start (t);
+ struct thread *cur = running_thread ();
+
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ /* Mark us as running. */
+ cur->status = THREAD_RUNNING;
+
+#ifdef USERPROG
+ /* Activate the new address space. */
+ addrspace_activate (cur);
+#endif
+
+ /* If the thread we switched from is dying, destroy it.
+ This must happen late because it's not a good idea to
+ e.g. destroy the page table you're currently using. */
+ if (prev != NULL && prev->status == THREAD_DYING)
+ destroy_thread (prev);
+}
+
+/* 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. */
+static void
+schedule (void)
+{
+ struct thread *cur = running_thread ();
+ struct thread *next = next_thread_to_run ();
+ struct thread *prev = NULL;
+
+ ASSERT (intr_get_level () == INTR_OFF);
+ ASSERT (cur->status != THREAD_RUNNING);
+ ASSERT (is_thread (next));
+
+ if (cur != next)
+ prev = switch_threads (cur, next);
+ schedule_tail (prev);
}
+\f
+/* Offset of `stack' member within `struct thread'.
+ Used by switch.S, which can't figure it out on its own. */
+uint32_t thread_stack_ofs = offsetof (struct thread, stack);
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