src/devices/intq.c

   1 #include "devices/intq.h"
   2 #include <debug.h>
   3 #include "threads/thread.h"
   4
   5 static int next (int pos);
   6 static void wait (struct intq *q, struct thread **waiter);
   7 static void signal (struct intq *q, struct thread **waiter);
   8
   9 /* Initializes interrupt queue Q. */
  10 void
  11 intq_init (struct intq *q)
  12 {
  13   lock_init (&q->lock);
  14   q->not_full = q->not_empty = NULL;
  15   q->head = q->tail = 0;
  16 }
  17
  18 /* Returns true if Q is empty, false otherwise. */
  19 bool
  20 intq_empty (const struct intq *q)
  21 {
  22   ASSERT (intr_get_level () == INTR_OFF);
  23   return q->head == q->tail;
  24 }
  25
  26 /* Returns true if Q is full, false otherwise. */
  27 bool
  28 intq_full (const struct intq *q)
  29 {
  30   ASSERT (intr_get_level () == INTR_OFF);
  31   return next (q->head) == q->tail;
  32 }
  33
  34 /* Removes a byte from Q and returns it.
  35    Q must not be empty if called from an interrupt handler.
  36    Otherwise, if Q is empty, first sleeps until a byte is
  37    added. */
  38 uint8_t
  39 intq_getc (struct intq *q)
  40 {
  41   uint8_t byte;
  42
  43   ASSERT (intr_get_level () == INTR_OFF);
  44   while (intq_empty (q))
  45     {
  46       ASSERT (!intr_context ());
  47       lock_acquire (&q->lock);
  48       wait (q, &q->not_empty);
  49       lock_release (&q->lock);
  50     }
  51
  52   byte = q->buf[q->tail];
  53   q->tail = next (q->tail);
  54   signal (q, &q->not_full);
  55   return byte;
  56 }
  57
  58 /* Adds BYTE to the end of Q.
  59    Q must not be full if called from an interrupt handler.
  60    Otherwise, if Q is full, first sleeps until a byte is
  61    removed. */
  62 void
  63 intq_putc (struct intq *q, uint8_t byte)
  64 {
  65   ASSERT (intr_get_level () == INTR_OFF);
  66   while (intq_full (q))
  67     {
  68       ASSERT (!intr_context ());
  69       lock_acquire (&q->lock);
  70       wait (q, &q->not_full);
  71       lock_release (&q->lock);
  72     }
  73
  74   q->buf[q->head] = byte;
  75   q->head = next (q->head);
  76   signal (q, &q->not_empty);
  77 }
  78 \f
  79 /* Returns the position after POS within an intq. */
  80 static int
  81 next (int pos)
  82 {
  83   return (pos + 1) % INTQ_BUFSIZE;
  84 }
  85
  86 /* WAITER must be the address of Q's not_empty or not_full
  87    member.  Waits until the given condition is true. */
  88 static void
  89 wait (struct intq *q UNUSED, struct thread **waiter)
  90 {
  91   ASSERT (!intr_context ());
  92   ASSERT (intr_get_level () == INTR_OFF);
  93   ASSERT ((waiter == &q->not_empty && intq_empty (q))
  94           || (waiter == &q->not_full && intq_full (q)));
  95
  96   *waiter = thread_current ();
  97   thread_block ();
  98 }
  99
 100 /* WAITER must be the address of Q's not_empty or not_full
 101    member, and the associated condition must be true.  If a
 102    thread is waiting for the condition, wakes it up and resets
 103    the waiting thread. */
 104 static void
 105 signal (struct intq *q UNUSED, struct thread **waiter)
 106 {
 107   ASSERT (intr_get_level () == INTR_OFF);
 108   ASSERT ((waiter == &q->not_empty && !intq_empty (q))
 109           || (waiter == &q->not_full && !intq_full (q)));
 110
 111   if (*waiter != NULL)
 112     {
 113       thread_unblock (*waiter);
 114       *waiter = NULL;
 115     }
 116 }