Merge branch 'task1/themis/thread-create-refactor' into 'master'

Refactor thread_create () to call thread_get_priority in order to retrieve priority

See merge request lab2425_autumn/pintos_22!21

.gitignore

@@ -4,8 +4,12 @@
 #ignore pdf files (just keep source files)
 *.pdf
 
-#ignore shell scripts (only used for testing)
-*.sh
+#ignore Mac OS generated files
+.DS_Store
+
+#ignore code editor generated directories
+.idea
+.vscode
 
 #ignore junk files from latex output
 *.out
@@ -27,3 +31,6 @@
 *.nav
 *.toc
 
+#ignore files from CLion/VSCode IDEs
+.idea
+.vscode

.gitlab-ci.yml

@@ -0,0 +1,44 @@
+stages:
+  - test
+
+.pintos_tests:
+  stage: test
+  image: gitlab.doc.ic.ac.uk:4567/lab2425_autumn/pintos_22/pintos-testing:latest
+  artifacts:
+    when: always
+    paths:
+      - src/$DIR/build/tests/$DIR/
+  before_script:
+    - cd src/utils
+    - make
+    - export PATH=$PWD:$PATH
+    - cd ../..
+  script:
+    - cd src/$DIR
+    - make check | tee build.log
+    - grep -q "FAIL tests/$DIR" build.log && exit 1 || exit 0
+
+test_devices:
+  extends: .pintos_tests
+  variables:
+    DIR: devices
+
+test_filesys:
+  extends: .pintos_tests
+  variables:
+    DIR: filesys
+
+test_threads:
+  extends: .pintos_tests
+  variables:
+    DIR: threads
+
+test_userprog:
+  extends: .pintos_tests
+  variables:
+    DIR: userprog
+
+test_vm:
+  extends: .pintos_tests
+  variables:
+    DIR: vm

Dockerfile.devel

@@ -0,0 +1,3 @@
+FROM debian:12-slim
+
+RUN apt update && apt install gcc perl make qemu-system-i386 gdb -y

src/devices/timer.c

@@ -119,9 +119,6 @@ timer_sleep (int64_t ticks)
                        NULL);
   intr_set_level (old_level);
   sema_down (&st.semaphore);
-  old_level = intr_disable ();
-  list_remove (&st.elem);
-  intr_set_level (old_level);
 }
 
 /* Sleeps for approximately MS milliseconds.  Interrupts must be
@@ -204,7 +201,10 @@ timer_interrupt (struct intr_frame *args UNUSED)
     {
       struct asleep_thread *st = list_entry (e, struct asleep_thread, elem);
       if (ticks >= st->end_at)
-        sema_up (&st->semaphore);
+        {
+          list_remove (&st->elem);
+          sema_up (&st->semaphore);
+        }
       else
         break;
     }

src/threads/fixed-point.h

@@ -0,0 +1,100 @@
+#include <stdint.h>
+#ifndef FIXED_POINT_H
+#define FIXED_POINT_H
+
+typedef struct
+  {
+    int32_t raw;
+  } fp32_t;
+
+/* Fixed Point Arithmetic bit count constants */
+#define NUM_FRAC_BITS 14
+#define NUM_INT_BITS (31 - NUM_FRAC_BITS)
+#define CONVERSION_FACTOR (1 << NUM_FRAC_BITS) /* f = 2^q, (2^14) */
+
+/* Fixed Point Arithmetic conversion operations */
+/* Converts an integer n to a fixed point number */
+inline fp32_t
+fp_from_int (int32_t n)
+{
+  return (fp32_t){ n * CONVERSION_FACTOR };
+}
+
+/* Handles conversion of fixed point to integer,
+   with truncation */
+inline int32_t
+fp_floor (fp32_t x)
+{
+  return x.raw / CONVERSION_FACTOR;
+}
+
+/* Handles conversion of fixed point to integer,
+   with rounding */
+inline int32_t
+fp_round (fp32_t x)
+{
+  if (x.raw >= 0)
+    return (x.raw + CONVERSION_FACTOR / 2) / CONVERSION_FACTOR;
+  else
+    return (x.raw - CONVERSION_FACTOR / 2) / CONVERSION_FACTOR;
+}
+
+/* Add two fixed points */
+inline fp32_t
+fp_add (fp32_t x, fp32_t y)
+{
+  return (fp32_t){ x.raw + y.raw };
+}
+
+/* Subtract two fixed points */
+inline fp32_t
+fp_sub (fp32_t x, fp32_t y)
+{
+  return (fp32_t){ x.raw - y.raw };
+}
+
+
+
+/* Multiple two fixed points */
+inline fp32_t
+fp_mul (fp32_t x, fp32_t y)
+{
+  return (fp32_t){ ((int64_t)x.raw) * y.raw / CONVERSION_FACTOR };
+}
+
+/* Divide two fixed points */
+inline fp32_t
+fp_div (fp32_t x, fp32_t y)
+{
+  return (fp32_t){ ((int64_t)x.raw) * CONVERSION_FACTOR / y.raw };
+}
+
+/* Multiply fixed point and integer */
+inline fp32_t
+fp_mul_int (fp32_t x, int32_t n)
+{
+  return (fp32_t){ x.raw * n };
+}
+
+/* Divide fixed point by integer */
+inline fp32_t
+fp_div_int (fp32_t x, int32_t n)
+{
+  return (fp32_t){ x.raw / n };
+}
+
+/* Add fixed point to integer */
+inline fp32_t
+fp_add_int (fp32_t x, int32_t n)
+{
+  return (fp32_t){ x.raw + n * CONVERSION_FACTOR };
+}
+
+/* Subtract integer from fixed point */
+inline fp32_t
+fp_sub_int (fp32_t x, int32_t n)
+{
+  return (fp32_t){ x.raw - n * CONVERSION_FACTOR };
+}
+
+#endif //FIXED_POINT_H

src/threads/synch.c

@@ -32,6 +32,10 @@
 #include "threads/interrupt.h"
 #include "threads/thread.h"
 
+static bool
+priority_less (const struct list_elem *a_, const struct list_elem *b_,
+               void *aux UNUSED);
+
 /* Initializes semaphore SEMA to VALUE.  A semaphore is a
    nonnegative integer along with two atomic operators for
    manipulating it:
@@ -68,8 +72,7 @@ sema_down (struct semaphore *sema)
   old_level = intr_disable ();
   while (sema->value == 0) 
     {
-      list_insert_ordered (&sema->waiters, &thread_current ()->elem,
-                           &thread_priority_greater, NULL);
+      list_push_back (&sema->waiters, &thread_current ()->elem);
       thread_block ();
     }
   sema->value--;
@@ -107,19 +110,31 @@ sema_try_down (struct semaphore *sema)
 
    This function may be called from an interrupt handler. */
 void
-sema_up (struct semaphore *sema) 
+sema_up (struct semaphore *sema)
 {
   enum intr_level old_level;
 
   ASSERT (sema != NULL);
 
   old_level = intr_disable ();
-  if (!list_empty (&sema->waiters)) 
-    thread_unblock (list_entry (list_pop_front (&sema->waiters),
-                                struct thread, elem));
+  if (!list_empty (&sema->waiters))
+    {
+      /* Enforces wake-up of the highest priority thread waiting for the
+         semaphore. */
+      struct list_elem *e = list_max (&sema->waiters, priority_less, NULL);
+      list_remove (e);
+      thread_unblock (list_entry (e, struct thread, elem));
+    }
   sema->value++;
   intr_set_level (old_level);
-  thread_yield ();
+
+  /* Yields the CPU in case the thread that has been woken up has a higher
+     priority that the current running thread, including the case when called
+     within an interrupt handler. */
+  if (intr_context ())
+    intr_yield_on_return ();
+  else
+    thread_yield ();
 }
 
 static void sema_test_helper (void *sema_);
@@ -183,6 +198,47 @@ lock_init (struct lock *lock)
   sema_init (&lock->semaphore, 1);
 }
 
+/* Current thread donates its priority to donee, iteratively
+   propagating the donation in the case of chains in the wait-for graph.
+   Also keeps track of the donation by updating the donors list. Expects
+   interrupts to be disabled. */
+static void
+donate_priority (struct thread *donee) {
+  ASSERT (intr_get_level () == INTR_OFF);
+
+  struct thread *donor = thread_current ();
+  list_push_back (&donee->donors_list, &donor->donor_elem);
+  
+  while (donee != NULL)
+    {
+      /* Stop propagation of donation once a donee is reached that has
+         a higher effective priority (as its donees can't have less
+         priority than that being donated). */
+      if (donor->priority <= donee->priority)
+          break;
+
+      /* Also stop propagation of donation once a donee is reached with
+         no donees of its own (sink node in WFG). */
+      if (donee->waiting_lock == NULL)
+        {
+          /* Only the sink node of the WFG isn't waiting for a lock and
+             could be on the ready list. Thus, as its priority changed,
+             it must be reinserted into the list. */
+          enum intr_level old_level = intr_disable ();
+          donee->priority = donor->priority;
+          ready_list_reinsert (donee);
+          intr_set_level (old_level);
+          
+          donee = NULL;
+        }
+      else
+        {
+          donee->priority = donor->priority;
+          donee = donee->waiting_lock->holder;
+        }
+    }
+}
+
 /* Acquires LOCK, sleeping until it becomes available if
    necessary.  The lock must not already be held by the current
    thread.
@@ -198,8 +254,19 @@ lock_acquire (struct lock *lock)
   ASSERT (!intr_context ());
   ASSERT (!lock_held_by_current_thread (lock));
 
+  struct thread *t = thread_current ();
+
+  enum intr_level old_level = intr_disable ();
+  if (lock->holder != NULL)
+    {
+      t->waiting_lock = lock;
+      donate_priority (lock->holder);
+    }
+  intr_set_level (old_level);
+
   sema_down (&lock->semaphore);
   lock->holder = thread_current ();
+  t->waiting_lock = NULL;
 }
 
 /* Tries to acquires LOCK and returns true if successful or false
@@ -233,8 +300,54 @@ lock_release (struct lock *lock)
   ASSERT (lock != NULL);
   ASSERT (lock_held_by_current_thread (lock));
 
+  struct thread *current_thread = thread_current ();
+  struct thread *max_donor = NULL;
+
+  struct list orphan_list;
+  list_init (&orphan_list);
+
+  enum intr_level old_level = intr_disable ();
+  /* Loop through current thread's donors, removing the ones waiting for the
+     lock being released and keeping track of them (within orphan_list).
+     Also identifies the highest priority donor thread among them. */
+  struct list_elem *tail = list_tail (&current_thread->donors_list);
+  struct list_elem *e = list_begin (&current_thread->donors_list);
+  while (e != tail)
+    {
+      struct thread *donor = list_entry (e, struct thread, donor_elem);
+      struct list_elem *next = list_next (e);
+
+      /* Excludes donors that aren't waiting for the lock being released,
+         and tracks the rest. */
+      if (donor->waiting_lock == lock)
+        {
+          list_remove (e);
+          list_push_back (&orphan_list, e);
+
+          /* Identify highest priority donor. */
+          if (max_donor == NULL || donor->priority > max_donor->priority)
+            max_donor = donor;
+        }
+
+      e = next;
+    }
+
+  /* If there exists a maximum donor thread waiting for this lock to be
+     released, transfer the remaining orphaned donors to its donor list. */
+  if (max_donor != NULL)
+    {
+      while (!list_empty (&orphan_list))
+        list_push_back (&max_donor->donors_list, list_pop_front (&orphan_list));
+    }
+
+  intr_set_level (old_level);
+  /* Removal of donors to this thread may change its effective priority,
+     so recalculate. */
+  thread_recalculate_priority ();
+
   lock->holder = NULL;
   sema_up (&lock->semaphore);
+  thread_yield ();
 }
 
 /* Returns true if the current thread holds LOCK, false
@@ -255,6 +368,49 @@ struct semaphore_elem
     struct semaphore semaphore;         /* This semaphore. */
   };
 
+/* Function that compares the two threads associated with the provided
+   pointers to their 'elem' member. Returns true if the thread associated
+   with a_ has a lower priority than that of b_. */
+static bool
+priority_less (const struct list_elem *a_, const struct list_elem *b_,
+               void *aux UNUSED)
+{
+  struct thread *a = list_entry (a_, struct thread, elem);
+  struct thread *b = list_entry (b_, struct thread, elem);
+
+  return a->priority < b->priority;
+}
+
+/* Function that compares the two *semaphores* associated with the provided
+   list_elem structures. [i.e., takes list_elem of semaphore_elem, and]
+   Returns true if the thread associated with the semaphore associated with a_
+   has a higher priority than that of b_.
+
+    If aux is provided, then it is a pointer to an integer representing the
+    priority of the first semaphore. This is useful when the thread has not been
+    sema'd down yet. */
+static bool
+sema_priority_more(const struct list_elem *a, const struct list_elem *b,
+                   void *inserting_telem)
+{
+  struct list_elem *te_a, *te_b;
+  
+  te_b = list_front (
+    &list_entry (b, struct semaphore_elem, elem)->semaphore.waiters);
+
+  if (inserting_telem == NULL)
+    {
+      te_a = list_front (
+        &list_entry (a, struct semaphore_elem, elem)->semaphore.waiters);
+    }
+  else
+    {
+      te_a = inserting_telem;
+    }
+
+  return priority_more (te_a, te_b, NULL);
+}
+
 /* Initializes condition variable COND.  A condition variable
    allows one piece of code to signal a condition and cooperating
    code to receive the signal and act upon it. */
@@ -318,9 +474,14 @@ cond_signal (struct condition *cond, struct lock *lock UNUSED)
   ASSERT (!intr_context ());
   ASSERT (lock_held_by_current_thread (lock));
 
-  if (!list_empty (&cond->waiters)) 
-    sema_up (&list_entry (list_pop_front (&cond->waiters),
-                          struct semaphore_elem, elem)->semaphore);
+  if (!list_empty (&cond->waiters))
+    {
+      /* Enforce wake-up of highest priority thread within the singleton 
+         semaphores waiting for condvar. */
+      struct list_elem *e = list_min (&cond->waiters, sema_priority_more, NULL);
+      list_remove (e);
+      sema_up (&list_entry (e, struct semaphore_elem, elem)->semaphore);
+    }
 }
 
 /* Wakes up all threads, if any, waiting on COND (protected by

src/threads/thread.c

@@ -4,6 +4,8 @@
 #include <random.h>
 #include <stdio.h>
 #include <string.h>
+#include "devices/timer.h"
+#include "threads/fixed-point.h"
 #include "threads/flags.h"
 #include "threads/interrupt.h"
 #include "threads/intr-stubs.h"
@@ -49,9 +51,11 @@ struct kernel_thread_frame
 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. */
+static fp32_t load_avg = { 0 }; /* System load average. */
 
 /* Scheduling. */
 #define TIME_SLICE 4            /* # of timer ticks to give each thread. */
+#define PRI_UPDATE_FREQ 4       /* # of timer ticks to update priorities. */
 static unsigned thread_ticks;   /* # of timer ticks since last yield. */
 
 /* If false (default), use round-robin scheduler.
@@ -64,12 +68,18 @@ 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 void init_thread (struct thread *, const char *name, int nice,
+                         int priority, fp32_t recent_cpu);
 static bool is_thread (struct thread *) UNUSED;
 static void *alloc_frame (struct thread *, size_t size);
+static int calculate_bsd_priority (fp32_t recent_cpu, int nice);
+static void update_recent_cpu (struct thread *t, void *aux UNUSED);
+static void recalculate_priority (struct thread *t);
 static void schedule (void);
 void thread_schedule_tail (struct thread *prev);
 static tid_t allocate_tid (void);
+static bool donor_priority_less (const struct list_elem *a_,
+                                 const struct list_elem *b_, void *aux UNUSED);
 
 /* Initializes the threading system by transforming the code
    that's currently running into a thread.  This can't work in
@@ -95,7 +105,9 @@ thread_init (void)
 
   /* Set up a thread structure for the running thread. */
   initial_thread = running_thread ();
-  init_thread (initial_thread, "main", PRI_DEFAULT);
+  fp32_t initial_thread_recent_cpu = { 0 };
+  init_thread (initial_thread, "main", NICE_DEFAULT, PRI_DEFAULT,
+               initial_thread_recent_cpu);
   initial_thread->status = THREAD_RUNNING;
   initial_thread->tid = allocate_tid ();
 }
@@ -145,6 +157,35 @@ thread_tick (void)
   else
     kernel_ticks++;
 
+  /* Update system load_avg and all threads recent_cpu every second. */
+  int64_t ticks = timer_ticks ();
+  if (thread_mlfqs)
+    {
+      if (t != idle_thread)
+          t->recent_cpu = fp_add_int (t->recent_cpu, 1);
+
+      if (ticks % TIMER_FREQ == 0)
+        {
+          size_t ready = threads_ready ();
+          if (t != idle_thread)
+            ready++;
+          fp32_t old_coeff = fp_div_int (fp_mul_int (load_avg, 59), 60);
+          fp32_t new_coeff = fp_div_int (fp_from_int (ready), 60);
+          load_avg = fp_add (old_coeff, new_coeff);
+
+          thread_foreach (update_recent_cpu, NULL);
+          /* Priorities have been updated, need to re-sort. */
+          list_sort (&ready_list, priority_more, NULL);
+        }
+
+      /* Recent cpu was updated, update priority. */
+      if (t != idle_thread && ticks % PRI_UPDATE_FREQ == 0)
+        {
+          t->base_priority = calculate_bsd_priority (t->recent_cpu, t->nice);
+          recalculate_priority (t);
+        }
+    }
+
   /* Enforce preemption. */
   if (++thread_ticks >= TIME_SLICE)
     intr_yield_on_return ();
@@ -192,7 +233,8 @@ thread_create (const char *name, int priority,
     return TID_ERROR;
 
   /* Initialize thread. */
-  init_thread (t, name, priority);
+  struct thread *parent_thread = thread_current ();
+  init_thread (t, name, parent_thread->nice, priority, parent_thread->recent_cpu);
   tid = t->tid = allocate_tid ();
 
   /* Prepare thread for first run by initializing its stack.
@@ -219,7 +261,11 @@ thread_create (const char *name, int priority,
 
   /* Add to run queue. */
   thread_unblock (t);
-  thread_yield ();
+
+  /* Yield if the newly created thread has higher priority than the current
+     thread. */
+  if (t->priority > thread_get_priority ())
+    thread_yield ();
 
   return tid;
 }
@@ -257,7 +303,10 @@ thread_unblock (struct thread *t)
 
   old_level = intr_disable ();
   ASSERT (t->status == THREAD_BLOCKED);
-  list_insert_ordered (&ready_list, &t->elem, &thread_priority_greater, NULL);
+
+  /* Insert the thread back into the ready list in priority order. */
+  list_insert_ordered (&ready_list, &t->elem, priority_more, NULL);
+
   t->status = THREAD_READY;
   intr_set_level (old_level);
 }
@@ -327,9 +376,13 @@ thread_yield (void)
   ASSERT (!intr_context ());
 
   old_level = intr_disable ();
-  if (cur != idle_thread) 
-    list_insert_ordered (&ready_list, &cur->elem, thread_priority_greater,
-                         NULL);
+
+  if (cur != idle_thread)
+    {
+      /* Insert the thread back into the ready list in priority order. */
+      list_insert_ordered (&ready_list, &cur->elem, priority_more, NULL);
+    }
+
   cur->status = THREAD_READY;
   schedule ();
   intr_set_level (old_level);
@@ -352,54 +405,161 @@ thread_foreach (thread_action_func *func, void *aux)
     }
 }
 
-/* Sets the current thread's priority to NEW_PRIORITY. */
-void
-thread_set_priority (int new_priority) 
+/* Function that compares the two threads associated with the provided
+   pointers to their 'elem' member. Returns true if the thread associated
+   with a_ has a higher priority than that of b_. */
+bool
+priority_more (const struct list_elem *a_, const struct list_elem *b_,
+               void *aux UNUSED)
 {
-  ASSERT (PRI_MIN <= new_priority && new_priority <= PRI_MAX);
-  int old_priority = thread_get_priority ();
+  struct thread *a = list_entry (a_, struct thread, elem);
+  struct thread *b = list_entry (b_, struct thread, elem);
+
+  return a->priority > b->priority;
 
-  thread_current ()->priority = new_priority;
-  if (new_priority < old_priority)
-    thread_yield ();
 }
 
-/* Returns the current thread's priority. */
+/* Function that compares the two threads associated with the provided
+   pointers to their 'donor_elem' member. Returns true if the thread associated
+   with a_ has a lower priority than that of b_. */
+static bool
+donor_priority_less (const struct list_elem *a_, const struct list_elem *b_,
+               void *aux UNUSED)
+{
+  struct thread *a = list_entry (a_, struct thread, donor_elem);
+  struct thread *b = list_entry (b_, struct thread, donor_elem);
+
+  return a->priority < b->priority;
+}
+
+/* Sets the current thread's base priority to new_base_priority.
+   Updates the current thread's effective priority if necessary. */
+void
+thread_set_priority (int new_base_priority)
+{
+
+  if (thread_mlfqs)
+    return;
+
+  ASSERT (new_base_priority >= PRI_MIN);
+  ASSERT (new_base_priority <= PRI_MAX);
+
+  struct thread *t = thread_current ();
+
+  /* If the base priority is unchanged, do nothing. */
+  if (new_base_priority == t->base_priority)
+    return;
+
+  t->base_priority = new_base_priority;
+  recalculate_priority (t);
+
+  thread_yield ();
+}
+
+/* Returns the current thread's effective priority. */
 int
 thread_get_priority (void) 
 {
   return thread_current ()->priority;
 }
 
+
+/* Updates recent_cpu for a thread. */
+static void
+update_recent_cpu (struct thread *t, void *aux UNUSED)
+{
+  fp32_t curr_recent_cpu = t->recent_cpu;
+  fp32_t dbl_load_avg = fp_mul_int (load_avg, 2);
+  fp32_t recent_cpu_coeff
+      = fp_div (dbl_load_avg, fp_add_int (dbl_load_avg, 1));
+  t->recent_cpu
+      = fp_add_int (fp_mul (recent_cpu_coeff, curr_recent_cpu), t->nice);
+  // recent_cpu was updated, update priority.
+  t->base_priority = calculate_bsd_priority (t->recent_cpu, t->nice);
+  recalculate_priority (t);
+}
+
+/* Recalculates the effective priority of the current thread. */
+void
+thread_recalculate_priority (void)
+{
+  struct thread *t = thread_current ();
+  recalculate_priority (t);
+}
+
+static void
+recalculate_priority (struct thread *t)
+{
+  enum intr_level old_level = intr_disable ();
+  t->priority = t->base_priority;
+
+  /* If there are no donors to the current thread, then the effective
+     priority is just the base priority. */
+  if (!list_empty (&t->donors_list))
+    {
+      int max_donated_priority =
+        list_entry (list_max (&t->donors_list, donor_priority_less, NULL),
+                    struct thread, donor_elem)->priority;
+
+      /* The effective priority is the max donated priority if this is
+         higher than the base priority. */
+      if (max_donated_priority > t->priority)
+        t->priority = max_donated_priority;
+    }
+  intr_set_level (old_level);
+}
+
 /* Sets the current thread's nice value to NICE. */
 void
-thread_set_nice (int nice UNUSED) 
+thread_set_nice (int nice)
 {
-  /* Not yet implemented. */
+  ASSERT (NICE_MIN <= nice && nice <= NICE_MAX);
+
+  struct thread *t = thread_current ();
+  t->nice = nice;
+  t->base_priority = calculate_bsd_priority (t->recent_cpu, t->nice);
+  recalculate_priority (t);
+  struct thread *next_t
+      = list_entry (list_begin (&ready_list), struct thread, elem);
+  if (t->priority < next_t->priority)
+    thread_yield ();
 }
 
 /* Returns the current thread's nice value. */
 int
 thread_get_nice (void) 
 {
-  /* Not yet implemented. */
-  return 0;
+  return thread_current ()->nice;
 }
 
 /* Returns 100 times the system load average. */
 int
 thread_get_load_avg (void) 
 {
-  /* Not yet implemented. */
-  return 0;
+  return fp_round (fp_mul_int (load_avg, 100));
 }
 
 /* Returns 100 times the current thread's recent_cpu value. */
 int
 thread_get_recent_cpu (void) 
 {
-  /* Not yet implemented. */
-  return 0;
+  return fp_round (fp_mul_int (thread_current ()->recent_cpu, 100));
+}
+
+/* Reinsert thread t into the ready list at its correct position
+   in descending order of priority. Used when this thread's priority
+   may have changed. Must be called with interrupts disabled. */
+void
+ready_list_reinsert (struct thread *t)
+{
+  ASSERT (intr_get_level () == INTR_OFF);
+
+  /* If the thread isn't ready to run, do nothing. */
+  if (t->status != THREAD_READY)
+    return;
+
+  list_remove (&t->elem);
+  list_insert_ordered (&ready_list, &t->elem, priority_more, NULL);
 }
 
 /* Idle thread.  Executes when no other thread is ready to run.
@@ -475,7 +635,8 @@ is_thread (struct thread *t)
 /* Does basic initialization of T as a blocked thread named
    NAME. */
 static void
-init_thread (struct thread *t, const char *name, int priority)
+init_thread (struct thread *t, const char *name, int nice, int priority,
+             fp32_t recent_cpu)
 {
   enum intr_level old_level;
 
@@ -487,9 +648,17 @@ init_thread (struct thread *t, const char *name, int priority)
   t->status = THREAD_BLOCKED;
   strlcpy (t->name, name, sizeof t->name);
   t->stack = (uint8_t *) t + PGSIZE;
-  t->priority = priority;
   t->magic = THREAD_MAGIC;
 
+  t->base_priority
+      = thread_mlfqs ? calculate_bsd_priority (recent_cpu, nice) : priority;
+  list_init (&t->donors_list);
+  t->waiting_lock = NULL;
+
+  t->nice = nice;
+  t->recent_cpu = recent_cpu;
+  t->priority = t->base_priority;
+
   old_level = intr_disable ();
   list_push_back (&all_list, &t->allelem);
   intr_set_level (old_level);
@@ -568,6 +737,21 @@ thread_schedule_tail (struct thread *prev)
     }
 }
 
+/* Calculates BSD priority for a thread */
+static int
+calculate_bsd_priority (fp32_t recent_cpu, int nice)
+{
+
+  ASSERT (thread_mlfqs);
+
+  int priority = PRI_MAX - (fp_round (recent_cpu) / 4) - (nice * 2);
+  if (priority < PRI_MIN)
+    return PRI_MIN;
+  if (priority > PRI_MAX)
+    return PRI_MAX;
+  return priority;
+}
+
 /* 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
@@ -605,17 +789,6 @@ allocate_tid (void)
   return tid;
 }
 
-/* Returns true iff the priority of the first list element's thread is greater
-   than that of the second list element's thread. */
-bool 
-thread_priority_greater (const struct list_elem *a, const struct list_elem *b,
-                         void *aux UNUSED)
-{
-  struct thread *ta = list_entry (a, struct thread, elem);
-  struct thread *tb = list_entry (b, struct thread, elem);
-  return ta->priority > tb->priority;
-}
-
 /* 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);

src/threads/thread.h

@@ -4,6 +4,7 @@
 #include <debug.h>
 #include <list.h>
 #include <stdint.h>
+#include "threads/fixed-point.h"
 
 /* States in a thread's life cycle. */
 enum thread_status
@@ -24,6 +25,10 @@ typedef int tid_t;
 #define PRI_DEFAULT 31                  /* Default priority. */
 #define PRI_MAX 63                      /* Highest priority. */
 
+#define NICE_MIN -20   /* Lowest niceness. */
+#define NICE_DEFAULT 0 /* Default niceness. */
+#define NICE_MAX 20    /* Highest niceness. */
+
 /* A kernel thread or user process.
 
    Each thread structure is stored in its own 4 kB page.  The
@@ -90,9 +95,23 @@ struct thread
     int priority;                       /* Priority. */
     struct list_elem allelem;           /* List element for all threads list. */
 
+    /* Donation Related */
+    int base_priority;                  /* Base priority of the thread. */
+    struct list donors_list;            /* List of threads that have donated
+                                           to this thread. */
+    struct lock *waiting_lock;          /* The lock that the current thread is
+                                           waiting for. */
+    struct list_elem donor_elem;        /* List element so that thread can be
+                                           enlisted in other donors list. */
+
+    /* MLFQS items */
+    int nice;                           /* Nice value for this thread */
+    fp32_t recent_cpu;                  /* Amount of time this process received */
+
     /* Shared between thread.c and synch.c. */
     struct list_elem elem;              /* List element. */
 
+
 #ifdef USERPROG
     /* Owned by userprog/process.c. */
     uint32_t *pagedir;                  /* Page directory. */
@@ -131,15 +150,17 @@ void thread_yield (void);
 typedef void thread_action_func (struct thread *t, void *aux);
 void thread_foreach (thread_action_func *, void *);
 
+bool priority_more (const struct list_elem *a_, const struct list_elem *b_,
+                    void *aux UNUSED);
 int thread_get_priority (void);
 void thread_set_priority (int);
+void thread_recalculate_priority (void);
 
 int thread_get_nice (void);
 void thread_set_nice (int);
 int thread_get_recent_cpu (void);
 int thread_get_load_avg (void);
 
-/* Returns true iff the priority of the first list element's thread is greater
-   than that of the second list element's thread. */
-list_less_func thread_priority_greater;
+void ready_list_reinsert (struct thread *t);
+
 #endif /* threads/thread.h */