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event.c

/* Copyright (c) 1993-2005 by Richard Kelsey and Jonathan Rees.
   See file COPYING. */

#include <signal.h>           /* for sigaction() (POSIX.1) */
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/times.h>
#include <errno.h>              /* for errno, (POSIX?/ANSI) */
#include <string.h>           /* FD_ZERO sometimes needs this */
#include "sysdep.h"
#include "c-mods.h"
#include "scheme48vm.h"
#include "event.h"

/* turning interrupts and I/O readiness into events */

#define block_interrupts()
#define allow_interrupts()

void        s48_when_keyboard_interrupt(int ign);
void        s48_when_alarm_interrupt(int ign);
static void     when_sigpipe_interrupt(int ign);
psbool            s48_setcatcher(int signum, void (*catcher)(int));
void        s48_start_alarm_interrupts(void);

void
s48_sysdep_init(void)
{
  if (!s48_setcatcher(SIGINT, s48_when_keyboard_interrupt)
      || !s48_setcatcher(SIGALRM, s48_when_alarm_interrupt)
      || !s48_setcatcher(SIGPIPE, when_sigpipe_interrupt)) {
    fprintf(stderr,
          "Failed to install signal handlers, errno = %d\n",
          errno);
    exit(1);
  }
  s48_start_alarm_interrupts();
}

/*
 * Unless a signal is being ignored, set up the handler.
 * If we return PSFALSE, something went wrong and errno is set to what.
 */

psbool
s48_setcatcher(int signum, void (*catcher)(int))
{
  struct sigaction      sa;

  if (sigaction(signum, (struct sigaction *)NULL, &sa) != 0)
    return (PSFALSE);
  if (sa.sa_handler == SIG_IGN)
    return (PSTRUE);
  sa.sa_handler = catcher;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = 0;
  if (sigaction(signum, &sa, (struct sigaction *)NULL) != 0)
    return (PSFALSE);
  return (PSTRUE);
}

static long keyboard_interrupt_count = 0;

void
s48_when_keyboard_interrupt(int ign)
{
  keyboard_interrupt_count += 1;
  NOTE_EVENT;
  return;
}

/*
   We turn off SIGPIPE interrupts by installing a handler that does nothing.
   Turning them off affects exec()'ed programs, so we don't want to do that.
   Any actual pipe problems are caught when we try to read or write to them.

   We thank Olin Shivers for this hack.
*/

static void
when_sigpipe_interrupt(int ign)
{
  return;
}

/* ticks since last timer-interrupt request */
long        s48_current_time = 0;

static long alarm_time = -1;
static long poll_time = -1;
static long poll_interval = 5;

void
s48_when_alarm_interrupt(int ign)
{
  s48_current_time += 1;
  /* fprintf(stderr, "[tick]"); */

  if ((alarm_time >= 0 && alarm_time <= s48_current_time) ||
      (poll_time >= 0 && poll_time <= s48_current_time)) {
    NOTE_EVENT;
  };
  return;
}

#define USEC_PER_POLL   (1000000 / POLLS_PER_SECOND)

/* delta is in ticks, 0 cancels current alarm */

long
s48_schedule_alarm_interrupt(long delta)
{
  long old;

  /*
  fprintf(stderr, "<scheduling alarm for %ld + %ld>\n", s48_current_time,
        delta/TICKS_PER_POLL); */

  /* get remaining time */
  if (alarm_time == -1)
    old = -1;
  else
    old = (alarm_time - s48_current_time) * TICKS_PER_POLL;

  /* decrement poll_time and reset current_time */
  if (poll_time != -1)
    poll_time -= s48_current_time;
  s48_current_time = 0;

  /* set alarm_time */
  if (delta == 0) {
    NOTE_EVENT;
    alarm_time = 0; }
  else
    alarm_time = delta / TICKS_PER_POLL;

  return old;
}

/* The next two procedures return times in seconds and ticks */

long
s48_real_time(long *ticks)
{
  struct timeval tv;
  static struct timeval tv_orig;
  static int initp = PSFALSE;
  if (!initp) {
    gettimeofday(&tv_orig, NULL);
    initp = PSTRUE;
  };
  gettimeofday(&tv, NULL);
  *ticks = (tv.tv_usec - tv_orig.tv_usec)/(1000000/TICKS_PER_SECOND);
  return tv.tv_sec - tv_orig.tv_sec;
}

long
s48_run_time(long *ticks)
{
  struct tms time_buffer;
  static long clock_tick = 0;
  long cpu_time;

  if (clock_tick == 0)
    clock_tick = sysconf(_SC_CLK_TCK); /* POSIX.1, POSIX.2 */
  times(&time_buffer);        /* On Sun, getrusage() would be better */

  cpu_time = time_buffer.tms_utime + time_buffer.tms_stime;

  *ticks = (cpu_time % clock_tick) * TICKS_PER_SECOND / clock_tick;
  return cpu_time / clock_tick;
}

void
s48_start_alarm_interrupts(void)
{
  struct itimerval newv, old;

  newv.it_value.tv_sec = 0;
  newv.it_value.tv_usec = USEC_PER_POLL;
  newv.it_interval.tv_sec = 0;
  newv.it_interval.tv_usec = USEC_PER_POLL;
  if (0 != setitimer(ITIMER_REAL, &newv, &old)) {
    perror("setitimer");
    exit(-1); }
}

void
s48_stop_alarm_interrupts(void)
{
  struct itimerval newv, old;

  newv.it_value.tv_sec = 0;
  newv.it_value.tv_usec = 0;
  newv.it_interval.tv_sec = 0;
  newv.it_interval.tv_usec = 0;
  if (0 != setitimer(ITIMER_REAL, &newv, &old)) {
    perror("setitimer");
    exit(-1); }
}


/*
 *  ; Scheme version of the get-next-event procedure
 *  ;
 *  ; 1. If there has been a keyboard interrupt, return it.
 *  ; 2. Check for ready ports if enough time has passed since the last check.
 *  ; 3. If there is a ready port, return it.
 *  ; 4. If an alarm is due, return it.
 *  ; 5. If no events are pending, clear the event flags.
 *  (define (get-next-event)
 *    (cond ((> *keyboard-interrupt-count* 0)
 *           (without-interrupts
 *             (lambda ()
 *              (set! *keyboard-interrupt-count*
 *                    (- *keyboard-interrupt-count* 1))))
 *           (values (enum event-type keyboard-interrupt) #f #f))
 *          (else
 *           (cond ((>= *current_time* *poll-time*)
 *                  (queue-ready-ports)
 *                  (set! *poll-time* (+ *time* *poll-interval*))))
 *           (cond ((not (queue-empty? ready-ports))
 *                  (values (enum event-type i/o-completion)
 *                          (dequeue! ready-ports)))
 *                 ((>= *current_time* *alarm-time*)
 *                  (set! *alarm-time* max-integer)
 *                  (values (enum event-type alarm-interrupt) #f))
 *                 (else
 *                  (without-interrupts
 *                    (lambda ()
 *                      (if (and (= *keyboard-interrupt-count* 0)
 *                               (> *alarm-time* *current_time*)
 *                               (> *poll-time* *current_time*))
 *                          (set! *pending-event?* #f))))
 *                  (values (enum event-type no-event) #f))))))
 */

static psbool     there_are_ready_ports(void);
static int  next_ready_port(void);
static int  queue_ready_ports(psbool wait, long seconds, long ticks);

int
s48_get_next_event(long *ready_fd, long *status)
{
  extern int s48_os_signal_pending(void);

  int io_poll_status;
  /*
    fprintf(stderr, "[poll at %d (waiting for %d)]\n", s48_current_time, alarm_time);
    */
  if (keyboard_interrupt_count > 0) {
    block_interrupts();
    --keyboard_interrupt_count;
    allow_interrupts();
    /* fprintf(stderr, "[keyboard interrupt]\n"); */
    return (KEYBOARD_INTERRUPT_EVENT);
  }
  if (poll_time != -1 && s48_current_time >= poll_time) {
    io_poll_status = queue_ready_ports(PSFALSE, 0, 0);
    if (io_poll_status == NO_ERRORS)
      poll_time = s48_current_time + poll_interval;
    else {
      *status = io_poll_status;
      return (ERROR_EVENT);
    }
  }
  if (there_are_ready_ports()) {
    *ready_fd = next_ready_port();
    *status = 0;   /* chars read or written */
    /* fprintf(stderr, "[i/o completion]\n"); */
    return (IO_COMPLETION_EVENT);
  }
  if (alarm_time != -1 && s48_current_time >= alarm_time) {
    alarm_time = -1;
    /* fprintf(stderr, "[alarm %ld]\n", ticks); */
    return (ALARM_EVENT);
  }
  if (s48_os_signal_pending())
    return (OS_SIGNAL_EVENT);
  block_interrupts();
  if ((keyboard_interrupt_count == 0)
      &&  (alarm_time == -1 || s48_current_time < alarm_time)
      &&  (poll_time == -1 || s48_current_time < poll_time))
    s48_Spending_eventsPS = PSFALSE;
  allow_interrupts();
  return (NO_EVENT);
}


/*
 * We keep two queues of ports: those that have a pending operation, and
 * those whose operation has completed.  Periodically, we call select() on
 * the pending ports and move any that are ready onto the other queue and
 * signal an event.
 */
#define FD_QUIESCENT 0              /* idle */
#define FD_READY     1              /* I/O ready to be performed */
#define FD_PENDING   2              /* waiting */

typedef struct fd_struct {
 int  fd,               /* file descriptor */
      status;                 /* one of the FD_* constants */
 psbool     is_input;         /* iff input */
 struct fd_struct *next;      /* next on same queue */
} fd_struct;


/*
 * A queue of fd_structs is empty iff the first field is NULL.  In
 * that case, lastp points to first.
 */
typedef struct fdque {
  fd_struct *first,
            **lastp;
} fdque;


static fd_struct  *fds[FD_SETSIZE];
static fdque      ready = {
                   NULL,
                   &ready.first
                  },
            pending = {
                     NULL,
                     &pending.first
                    };


static void       findrm(fd_struct *entry, fdque *que);
static fd_struct  *rmque(fd_struct **link, fdque *que);
static void       addque(fd_struct *entry, fdque *que);
static fd_struct  *add_fd(int fd, psbool is_input);


/*
 * Find a fd_struct in a queue, and remove it.
 */
static void
findrm(fd_struct *entry, fdque *que)
{
  fd_struct **fp,
    *f;

  for (fp = &que->first; (f = *fp) != entry; fp = &f->next)
    if (f == NULL) {
      fprintf(stderr, "ERROR: findrm fd %d, status %d not on queue.\n",
            entry->fd, entry->status);
      return;
    }
  rmque(fp, que);
}


/*
 * Given a pointer to the link of a fd_struct, and a pointer to
 * the queue it is on, remove the entry from the queue.
 * The entry removed is returned.
 */
static fd_struct  *
rmque(fd_struct **link, fdque *que)
{
  fd_struct *res;

  res = *link;
  *link = res->next;
  if (res->next == NULL)
    que->lastp = link;
  return (res);
}


/*
 * Add a fd_struct to a queue.
 */
static void
addque(fd_struct *entry, fdque *que)
{
  *que->lastp = entry;
  entry->next = NULL;
  que->lastp = &entry->next;
}


static psbool
there_are_ready_ports(void)
{
  return (ready.first != NULL);
}


static int
next_ready_port(void)
{
  fd_struct *p;

  p = rmque(&ready.first, &ready);
  p->status = FD_QUIESCENT;
  return (p->fd);
}


/*
 * Put fd on to the queue of ports with pending operations.
 * Return PSTRUE if successful, and PSFALSE otherwise.
 */
psbool
s48_add_pending_fd(int fd, psbool is_input)
{
  fd_struct *data;

  if (! (0 <= fd && fd < FD_SETSIZE)) {
    fprintf(stderr, "ERROR: add_pending fd %d not in [0, %d)\n",
          fd,
          FD_SETSIZE);
    return (PSFALSE);
  }
  data = fds[fd];
  if (data == NULL) {
    data = add_fd(fd, is_input);
    if (data == NULL)
      return (PSFALSE); }           /* no more memory */

  data->is_input = is_input;

  if (data->status == FD_PENDING)
    return (PSTRUE);                /* fd is already pending */

  if (data->status == FD_READY)
    findrm(data, &ready);
  data->status = FD_PENDING;
  addque(data, &pending);
  if (poll_time == -1)
    poll_time = s48_current_time + poll_interval;
  return PSTRUE;
}


/*
 * Add a new fd_struct for fd.
 */
static fd_struct  *
add_fd(int fd, psbool is_input)
{
  struct fd_struct      *new_fd;

  new_fd = (struct fd_struct *)malloc(sizeof(struct fd_struct));
  if (new_fd != NULL) {
    new_fd->fd = fd;
    new_fd->status = FD_QUIESCENT;
    new_fd->is_input = is_input;
    new_fd->next = NULL;
    fds[fd] = new_fd;
  }
  return (new_fd);
}


/*
 * Remove fd from any queues it is on.  Returns true if the FD was on a queue
 * and false if it wasn't.
 */
psbool
s48_remove_fd(int fd)
{
  struct fd_struct      *data;

  if (! (0 <= fd && fd < FD_SETSIZE)) {
    fprintf(stderr, "ERROR: s48_remove_fd fd %d not in [0, %d)\n",
          fd,
          FD_SETSIZE);
    return PSFALSE;
  }
  data = fds[fd];
  if (data == NULL)
    return PSFALSE;
  if (data->status == FD_PENDING) {
    findrm(data, &pending);
    if (pending.first == NULL)
      poll_time = -1;
  } else if (data->status == FD_READY)
    findrm(data, &ready);
  free((void *)data);
  fds[fd] = NULL;
  return PSTRUE;
}


int
s48_wait_for_event(long max_wait, psbool is_minutes)
{
  int status;
  long      seconds,
      ticks;

  /* fprintf(stderr, "[waiting]\n"); */

  s48_stop_alarm_interrupts();
  ticks = 0;
  if (max_wait == -1)
    seconds = -1;
  else if (is_minutes)
    seconds = max_wait * 60;
  else {
    seconds = max_wait / TICKS_PER_SECOND;
    ticks = max_wait % TICKS_PER_SECOND;
  }
  if (keyboard_interrupt_count > 0)
    status = NO_ERRORS;
  else {
    status = queue_ready_ports(PSTRUE, seconds, ticks);
    if (there_are_ready_ports())
      NOTE_EVENT;
  }
  s48_start_alarm_interrupts();
  return (status);
}


/*
 * Call select() on the pending ports and move any ready ones to the ready
 * queue.  If wait is true, seconds is either -1 (wait forever) or the
 * maximum number of seconds to wait (with ticks any additional ticks).
 * The returned value is a status code.
 */
static int
queue_ready_ports(psbool wait, long seconds, long ticks)
{
  fd_set    reads,
            writes,
            alls;
  int       limfd;
  fd_struct *fdp,
            **fdpp;
  int       left;
  struct timeval  tv,
                  *tvp;

  if ((! wait)
      &&  (pending.first == NULL))
    return (NO_ERRORS);
  FD_ZERO(&reads);
  FD_ZERO(&writes);
  FD_ZERO(&alls);
  limfd = 0;
  for (fdp = pending.first; fdp != NULL; fdp = fdp->next) {
    FD_SET(fdp->fd, fdp->is_input ? &reads : &writes);
    FD_SET(fdp->fd, &alls);
    if (limfd <= fdp->fd)
      limfd = fdp->fd + 1;
  }
  tvp = &tv;
  if (wait)
    if (seconds == -1)
      tvp = NULL;
    else {
      tv.tv_sec = seconds;
      tv.tv_usec = ticks * (1000000 / TICKS_PER_SECOND);
    }
  else
    timerclear(&tv);
  while(1) {
    left = select(limfd, &reads, &writes, &alls, tvp);
    if (left > 0) {
      fdpp = &pending.first;
      while (left > 0 && (fdp = *fdpp) != NULL)
      if ((FD_ISSET(fdp->fd, &alls))
          ||  (FD_ISSET(fdp->fd, fdp->is_input ? &reads : &writes))) {
        --left;
        rmque(fdpp, &pending);
        fdp->status = FD_READY;
        addque(fdp, &ready);
      } else
        fdpp = &fdp->next;
      if (pending.first == NULL)
      poll_time = -1;
      return NO_ERRORS;
    }
    else if (left == 0)
      return NO_ERRORS;
    else if (errno == EINTR) {
      tvp = &tv;        /* turn off blocking and try again */
      timerclear(tvp);
    }       
    else
      return errno;
  }
}

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