-#include "thread.h"
+#include "threads/thread.h"
+#include <debug.h>
#include <stddef.h>
-#include "debug.h"
-#include "interrupt.h"
-#include "lib.h"
-#include "mmu.h"
-#include "palloc.h"
-#include "random.h"
-#include "switch.h"
+#include <random.h>
+#include <stdio.h>
+#include <string.h>
+#include "threads/flags.h"
+#include "threads/interrupt.h"
+#include "threads/intr-stubs.h"
+#include "threads/palloc.h"
+#include "threads/switch.h"
+#include "threads/synch.h"
+#include "threads/vaddr.h"
+#ifdef USERPROG
+#include "userprog/process.h"
+#endif
-uint32_t thread_stack_ofs = offsetof (struct thread, stack);
+/* Random 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 0xcd6abf4b
-static struct list run_queue;
+/* List of processes in THREAD_READY state, that is, processes
+ that are ready to run but not actually running. */
+static struct list ready_list;
-void
-thread_init (void)
-{
- list_init (&run_queue);
-}
+/* List of all processes. Processes are added to this list
+ when they are first scheduled and removed when they exit. */
+static struct list all_list;
+
+/* Idle thread. */
+static struct thread *idle_thread;
+
+/* Initial thread, the thread running init.c:main(). */
+static struct thread *initial_thread;
-struct thread_root_frame
+/* Lock used by allocate_tid(). */
+static struct lock tid_lock;
+
+/* 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)
+/* Statistics. */
+static long long idle_ticks; /* # of timer ticks spent idle. */
+static long long kernel_ticks; /* # of timer ticks in kernel threads. */
+static long long user_ticks; /* # of timer ticks in user programs. */
+
+/* Scheduling. */
+#define TIME_SLICE 4 /* # of timer ticks to give each thread. */
+static unsigned thread_ticks; /* # of timer ticks since last yield. */
+
+/* If false (default), use round-robin scheduler.
+ If true, use multi-level feedback queue scheduler.
+ Controlled by kernel command-line option "-o mlfqs". */
+bool thread_mlfqs;
+
+static void kernel_thread (thread_func *, void *aux);
+
+static void idle (void *aux UNUSED);
+static struct thread *running_thread (void);
+static struct thread *next_thread_to_run (void);
+static void init_thread (struct thread *, const char *name, int priority);
+static bool is_thread (struct thread *) UNUSED;
+static void *alloc_frame (struct thread *, size_t size);
+static void schedule (void);
+void thread_schedule_tail (struct thread *prev);
+static tid_t allocate_tid (void);
+
+/* Initializes the threading system by transforming the code
+ 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
+ thread_create().
+
+ It is not safe to call thread_current() until this function
+ finishes. */
+void
+thread_init (void)
{
- ASSERT (function != NULL);
-
- function (aux);
- thread_exit ();
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ lock_init (&tid_lock);
+ list_init (&ready_list);
+ list_init (&all_list);
+
+ /* Set up a thread structure for the running thread. */
+ initial_thread = running_thread ();
+ init_thread (initial_thread, "main", PRI_DEFAULT);
+ initial_thread->status = THREAD_RUNNING;
+ initial_thread->tid = allocate_tid ();
}
-static struct thread *
-new_thread (const char *name)
+/* Starts preemptive thread scheduling by enabling interrupts.
+ Also creates the idle thread. */
+void
+thread_start (void)
{
- struct thread *t;
+ /* Create the idle thread. */
+ struct semaphore idle_started;
+ sema_init (&idle_started, 0);
+ thread_create ("idle", PRI_MIN, idle, &idle_started);
- 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;
+ /* Start preemptive thread scheduling. */
+ intr_enable ();
+
+ /* Wait for the idle thread to initialize idle_thread. */
+ sema_down (&idle_started);
}
-static void *
-alloc_frame (struct thread *t, size_t size)
+/* Called by the timer interrupt handler at each timer tick.
+ Thus, this function runs in an external interrupt context. */
+void
+thread_tick (void)
{
- ASSERT (size % sizeof (uint32_t) == 0);
+ struct thread *t = thread_current ();
- t->stack -= size;
- return t->stack;
+ /* Update statistics. */
+ if (t == idle_thread)
+ idle_ticks++;
+#ifdef USERPROG
+ else if (t->pagedir != NULL)
+ user_ticks++;
+#endif
+ else
+ kernel_ticks++;
+
+ /* Enforce preemption. */
+ if (++thread_ticks >= TIME_SLICE)
+ intr_yield_on_return ();
}
-struct thread *
-thread_create (const char *name, void (*function) (void *aux), void *aux)
+/* Prints thread statistics. */
+void
+thread_print_stats (void)
+{
+ printf ("Thread: %lld idle ticks, %lld kernel ticks, %lld user ticks\n",
+ idle_ticks, kernel_ticks, user_ticks);
+}
+
+/* Creates a new kernel thread named NAME with the given initial
+ PRIORITY, which executes FUNCTION passing AUX as the argument,
+ and adds it to the ready queue. Returns the thread identifier
+ for the new thread, or TID_ERROR if creation fails.
+
+ If thread_start() has been called, then the new thread may be
+ scheduled before thread_create() returns. It could even exit
+ before thread_create() returns. Contrariwise, the original
+ thread may run for any amount of time before the new thread is
+ scheduled. Use a semaphore or some other form of
+ synchronization if you need to ensure ordering.
+
+ The code provided sets the new thread's `priority' member to
+ PRIORITY, but no actual priority scheduling is implemented.
+ Priority scheduling is the goal of Problem 1-3. */
+tid_t
+thread_create (const char *name, int priority,
+ thread_func *function, void *aux)
{
struct thread *t;
- struct thread_root_frame *rf;
- struct switch_thunk_frame *tf;
- struct switch_frame *sf;
+ struct kernel_thread_frame *kf;
+ struct switch_entry_frame *ef;
+ struct switch_threads_frame *sf;
+ tid_t tid;
+ enum intr_level old_level;
ASSERT (function != NULL);
- t = new_thread (name);
+ /* Allocate thread. */
+ t = palloc_get_page (PAL_ZERO);
+ if (t == NULL)
+ return TID_ERROR;
+
+ /* Initialize thread. */
+ init_thread (t, name, priority);
+ tid = t->tid = allocate_tid ();
+
+ /* Prepare thread for first run by initializing its stack.
+ Do this atomically so intermediate values for the 'stack'
+ member cannot be observed. */
+ old_level = intr_disable ();
- /* 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_thunk(). */
- tf = alloc_frame (t, sizeof *tf);
- tf->eip = (void (*) (void)) thread_root;
+ /* Stack frame for switch_entry(). */
+ ef = alloc_frame (t, sizeof *ef);
+ ef->eip = (void (*) (void)) kernel_thread;
- /* Stack frame for thread_switch(). */
+ /* Stack frame for switch_threads(). */
sf = alloc_frame (t, sizeof *sf);
- sf->eip = (void (*) (void)) switch_thunk;
+ sf->eip = switch_entry;
+ sf->ebp = 0;
+
+ intr_set_level (old_level);
/* Add to run queue. */
- thread_ready (t);
+ thread_unblock (t);
- return t;
+ return tid;
}
-struct thread *
-thread_current (void)
-{
- uint32_t *esp;
- asm ("movl %%esp, %0\n" : "=g" (esp));
- return pg_round_down (esp);
-}
+/* Puts the current thread to sleep. It will not be scheduled
+ again until awoken by thread_unblock().
-#ifdef USERPROG
-bool
-thread_execute (const char *filename)
+ 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)
{
- struct thread *t = new_thread (filename);
- if (t == NULL)
- return false;
-
- if (!addrspace_load (&t->addrspace, filename))
- panic ("%s: program load failed", filename);
- printk ("%s: loaded\n", filename);
- return true;
+ ASSERT (!intr_context ());
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ thread_current ()->status = THREAD_BLOCKED;
+ schedule ();
}
-#endif
+/* 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.)
+
+ This function does not preempt the running thread. This can
+ be important: if the caller had disabled interrupts itself,
+ it may expect that it can atomically unblock a thread and
+ update other data. */
void
-thread_ready (struct thread *t)
+thread_unblock (struct thread *t)
{
- if (t->status != THREAD_READY)
- {
- list_push_back (&run_queue, &t->rq_elem);
- t->status = THREAD_READY;
- }
+ enum intr_level old_level;
+
+ ASSERT (is_thread (t));
+
+ old_level = intr_disable ();
+ ASSERT (t->status == THREAD_BLOCKED);
+ list_push_back (&ready_list, &t->elem);
+ t->status = THREAD_READY;
+ intr_set_level (old_level);
}
-static struct thread *
-find_next_to_run (void)
+/* Returns the name of the running thread. */
+const char *
+thread_name (void)
{
- if (list_empty (&run_queue))
- return NULL;
- else
- return list_entry (list_pop_front (&run_queue), struct thread, rq_elem);
+ return thread_current ()->name;
}
-static void
-idle (void)
+/* 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)
{
- static int idle = 0;
- if (idle++ == 0)
- printk ("idle\n");
+ 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);
+
+ return t;
}
-void
-thread_destroy (struct thread *t)
+/* Returns the running thread's tid. */
+tid_t
+thread_tid (void)
{
- ASSERT (t->status == THREAD_DYING);
- ASSERT (t != thread_current ());
-
- palloc_free (t);
+ return thread_current ()->tid;
}
+/* Deschedules the current thread and destroys it. Never
+ returns to the caller. */
void
-thread_schedule (void)
+thread_exit (void)
{
- struct thread *cur, *next, *prev;
-
- ASSERT (intr_get_level () == IF_OFF);
-
- cur = thread_current ();
- ASSERT (cur->status != THREAD_RUNNING);
-
- while ((next = find_next_to_run ()) == NULL)
- idle ();
-
- next->status = THREAD_RUNNING;
- prev = switch_threads (cur, next);
-
- /* Prevent GCC from reordering anything around the thread
- switch. */
- asm volatile ("" : : : "memory");
+ ASSERT (!intr_context ());
#ifdef USERPROG
- addrspace_activate (&cur->addrspace);
+ process_exit ();
#endif
- if (prev != NULL && prev->status == THREAD_DYING)
- thread_destroy (prev);
-
- intr_enable ();
+ /* Remove thread from all threads list, set our status to dying,
+ and schedule another process. That process will destroy us
+ when it calls thread_schedule_tail(). */
+ intr_disable ();
+ list_remove (&thread_current()->allelem);
+ 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
thread_yield (void)
{
+ struct thread *cur = thread_current ();
+ enum intr_level old_level;
+
ASSERT (!intr_context ());
- intr_disable ();
- thread_ready (thread_current ());
- thread_schedule ();
+ old_level = intr_disable ();
+ if (cur != idle_thread)
+ list_push_back (&ready_list, &cur->elem);
+ cur->status = THREAD_READY;
+ schedule ();
+ intr_set_level (old_level);
}
+/* Invoke function 'func' on all threads, passing along 'aux'.
+ This function must be called with interrupts off. */
void
-thread_start (struct thread *t)
+thread_foreach (thread_action_func *func, void *aux)
{
- ASSERT (intr_get_level () == IF_OFF);
+ struct list_elem *e;
+
+ ASSERT (intr_get_level () == INTR_OFF);
- if (t->status == THREAD_READY)
- list_remove (&t->rq_elem);
- t->status = THREAD_RUNNING;
- switch_threads (NULL, t);
+ for (e = list_begin (&all_list); e != list_end (&all_list);
+ e = list_next (e))
+ {
+ struct thread *t = list_entry (e, struct thread, allelem);
+ func (t, aux);
+ }
}
+/* Sets the current thread's priority to NEW_PRIORITY. */
void
-thread_exit (void)
+thread_set_priority (int new_priority)
{
- ASSERT (!intr_context ());
+ thread_current ()->priority = new_priority;
+}
- intr_disable ();
- thread_current ()->status = THREAD_DYING;
- thread_schedule ();
+/* Returns the current thread's priority. */
+int
+thread_get_priority (void)
+{
+ return thread_current ()->priority;
}
+/* Sets the current thread's nice value to NICE. */
void
-thread_sleep (void)
+thread_set_nice (int nice UNUSED)
{
- ASSERT (!intr_context ());
- ASSERT (intr_get_level () == IF_OFF);
+ /* Not yet implemented. */
+}
- thread_current ()->status = THREAD_BLOCKED;
- thread_schedule ();
+/* Returns the current thread's nice value. */
+int
+thread_get_nice (void)
+{
+ /* Not yet implemented. */
+ return 0;
}
+/* Returns 100 times the system load average. */
+int
+thread_get_load_avg (void)
+{
+ /* Not yet implemented. */
+ return 0;
+}
+
+/* Returns 100 times the current thread's recent_cpu value. */
+int
+thread_get_recent_cpu (void)
+{
+ /* Not yet implemented. */
+ return 0;
+}
+\f
+/* Idle thread. Executes when no other thread is ready to run.
+
+ The idle thread is initially put on the ready list by
+ thread_start(). It will be scheduled once initially, at which
+ point it initializes idle_thread, "up"s the semaphore passed
+ to it to enable thread_start() to continue, and immediately
+ blocks. After that, the idle thread never appears in the
+ ready list. It is returned by next_thread_to_run() as a
+ special case when the ready list is empty. */
static void
-tfunc (void *aux UNUSED)
+idle (void *idle_started_ UNUSED)
{
+ struct semaphore *idle_started = idle_started_;
+ idle_thread = thread_current ();
+ sema_up (idle_started);
+
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);
+ /* Let someone else run. */
+ intr_disable ();
+ thread_block ();
+
+ /* Re-enable interrupts and wait for the next one.
+
+ The `sti' instruction disables interrupts until the
+ completion of the next instruction, so these two
+ instructions are executed atomically. This atomicity is
+ important; otherwise, an interrupt could be handled
+ between re-enabling interrupts and waiting for the next
+ one to occur, wasting as much as one clock tick worth of
+ time.
+
+ See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3a]
+ 7.11.1 "HLT Instruction". */
+ asm volatile ("sti; hlt" : : : "memory");
}
}
+/* Function used as the basis for a kernel thread. */
+static void
+kernel_thread (thread_func *function, void *aux)
+{
+ ASSERT (function != NULL);
+
+ 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;
+
+ /* 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 ("mov %%esp, %0" : "=g" (esp));
+ return pg_round_down (esp);
+}
+
+/* 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;
+}
+
+/* Does basic initialization of T as a blocked thread named
+ NAME. */
+static void
+init_thread (struct thread *t, const char *name, int priority)
+{
+ enum intr_level old_level;
+
+ ASSERT (t != NULL);
+ ASSERT (PRI_MIN <= priority && priority <= PRI_MAX);
+ ASSERT (name != NULL);
+
+ memset (t, 0, sizeof *t);
+ t->status = THREAD_BLOCKED;
+ strlcpy (t->name, name, sizeof t->name);
+ t->stack = (uint8_t *) t + PGSIZE;
+ t->priority = priority;
+ t->magic = THREAD_MAGIC;
+
+ old_level = intr_disable ();
+ list_push_back (&all_list, &t->allelem);
+ intr_set_level (old_level);
+}
+
+/* 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)
+{
+ /* Stack data is always allocated in word-size units. */
+ ASSERT (is_thread (t));
+ ASSERT (size % sizeof (uint32_t) == 0);
+
+ t->stack -= size;
+ return t->stack;
+}
+
+/* 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)
+{
+ if (list_empty (&ready_list))
+ return idle_thread;
+ else
+ return list_entry (list_pop_front (&ready_list), struct thread, elem);
+}
+
+/* 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).
+
+ 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
-thread_self_test (void)
+thread_schedule_tail (struct thread *prev)
{
- struct thread *t;
- int i;
-
- for (i = 0; i < 4; i++)
+ struct thread *cur = running_thread ();
+
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ /* Mark us as running. */
+ cur->status = THREAD_RUNNING;
+
+ /* Start new time slice. */
+ thread_ticks = 0;
+
+#ifdef USERPROG
+ /* Activate the new address space. */
+ process_activate ();
+#endif
+
+ /* If the thread we switched from is dying, destroy its struct
+ thread. This must happen late so that thread_exit() doesn't
+ pull out the rug under itself. (We don't free
+ initial_thread because its memory was not obtained via
+ palloc().) */
+ if (prev != NULL && prev->status == THREAD_DYING && prev != initial_thread)
{
- char name[2];
- name[0] = 'a' + i;
- name[1] = 0;
- t = thread_create (name, tfunc, NULL);
+ ASSERT (prev != cur);
+ palloc_free_page (prev);
}
- thread_start (t);
}
+
+/* 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.
+
+ It's not safe to call printf() until thread_schedule_tail()
+ has completed. */
+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);
+ thread_schedule_tail (prev);
+}
+
+/* Returns a tid to use for a new thread. */
+static tid_t
+allocate_tid (void)
+{
+ static tid_t next_tid = 1;
+ tid_t tid;
+
+ lock_acquire (&tid_lock);
+ tid = next_tid++;
+ lock_release (&tid_lock);
+
+ return tid;
+}
+\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);
projects / pintos-anon / blobdiff