text: /* -----------------------------------------------------------------------------
   *
   * (c) The GHC Team, 1998-2005
   *
   * Signal processing / handling.
   *
   * ---------------------------------------------------------------------------*/
  
  #include "PosixSource.h"
  #include "Rts.h"
  
  #include "Schedule.h"
  #include "RtsSignals.h"
  #include "Signals.h"
  #include "RtsUtils.h"
  #include "Prelude.h"
  #include "Stable.h"
  
  #ifdef alpha_HOST_ARCH
  # if defined(linux_HOST_OS)
  #  include <asm/fpu.h>
  # else
  #  include <machine/fpu.h>
  # endif
  #endif
  
  #ifdef HAVE_UNISTD_H
  # include <unistd.h>
  #endif
  
  #ifdef HAVE_SIGNAL_H
  # include <signal.h>
  #endif
  
  #ifdef HAVE_ERRNO_H
  # include <errno.h>
  #endif
  
  #ifdef HAVE_EVENTFD_H
  # include <sys/eventfd.h>
  #endif
  
  #ifdef HAVE_TERMIOS_H
  #include <termios.h>
  #endif
  
  #include <stdlib.h>
  #include <string.h>
  
  /* This curious flag is provided for the benefit of the Haskell binding
   * to POSIX.1 to control whether or not to include SA_NOCLDSTOP when
   * installing a SIGCHLD handler.
   */
  HsInt nocldstop = 0;
  
  /* -----------------------------------------------------------------------------
   * The table of signal handlers
   * -------------------------------------------------------------------------- */
  
  #if defined(RTS_USER_SIGNALS)
  
  /* SUP: The type of handlers is a little bit, well, doubtful... */
  StgInt *signal_handlers = NULL; /* Dynamically grown array of signal handlers */
  static StgInt nHandlers = 0;    /* Size of handlers array */
  
  static nat n_haskell_handlers = 0;
  
  static sigset_t userSignals;
  static sigset_t savedSignals;
  
  #ifdef THREADED_RTS
  static Mutex sig_mutex; // protects signal_handlers, nHandlers
  #endif
  
  /* -----------------------------------------------------------------------------
   * Initialisation / deinitialisation
   * -------------------------------------------------------------------------- */
  
  void
  initUserSignals(void)
  {
      sigemptyset(&userSignals);
  #ifdef THREADED_RTS
      initMutex(&sig_mutex);
  #endif
  }
  
  void
  freeSignalHandlers(void) {
      if (signal_handlers != NULL) {
          stgFree(signal_handlers);
          signal_handlers = NULL;
          nHandlers = 0;
          n_haskell_handlers = 0;
      }
  #ifdef THREADED_RTS
      closeMutex(&sig_mutex);
  #endif
  }
  
  /* -----------------------------------------------------------------------------
   * Allocate/resize the table of signal handlers.
   * -------------------------------------------------------------------------- */
  
  static void
  more_handlers(int sig)
  {
      StgInt i;
  
      if (sig < nHandlers)
          return;
  
      if (signal_handlers == NULL)
          signal_handlers = (StgInt *)stgMallocBytes((sig + 1) * sizeof(StgInt),
                                                     "more_handlers");
      else
          signal_handlers = (StgInt *)stgReallocBytes(signal_handlers,
                                                      (sig + 1) * sizeof(StgInt),
                                                      "more_handlers");
  
      for(i = nHandlers; i <= sig; i++)
          // Fill in the new slots with default actions
          signal_handlers[i] = STG_SIG_DFL;
  
      nHandlers = sig + 1;
  }
  
  // Here's the pipe into which we will send our signals
  static int io_manager_wakeup_fd = -1;
  static int timer_manager_control_wr_fd = -1;
  
  #define IO_MANAGER_WAKEUP 0xff
  #define IO_MANAGER_DIE    0xfe
  #define IO_MANAGER_SYNC   0xfd
  
  void setTimerManagerControlFd(int fd) {
      timer_manager_control_wr_fd = fd;
  }
  
  void
  setIOManagerWakeupFd (int fd)
  {
      // only called when THREADED_RTS, but unconditionally
      // compiled here because GHC.Event.Control depends on it.
      io_manager_wakeup_fd = fd;
  }
  
  /* -----------------------------------------------------------------------------
   * Wake up at least one IO or timer manager HS thread.
   * -------------------------------------------------------------------------- */
  void
  ioManagerWakeup (void)
  {
      int r;
      // Wake up the IO Manager thread by sending a byte down its pipe
      if (io_manager_wakeup_fd >= 0) {
  #if defined(HAVE_EVENTFD)
          StgWord64 n = (StgWord64)IO_MANAGER_WAKEUP;
          r = write(io_manager_wakeup_fd, (char *) &n, 8);
  #else
          StgWord8 byte = (StgWord8)IO_MANAGER_WAKEUP;
          r = write(io_manager_wakeup_fd, &byte, 1);
  #endif
          if (r == -1) { sysErrorBelch("ioManagerWakeup: write"); }
      }
  }
  
  #if defined(THREADED_RTS)
  void
  ioManagerDie (void)
  {
      StgWord8 byte = (StgWord8)IO_MANAGER_DIE;
      nat i;
      int fd;
      int r;
  
      if (0 <= timer_manager_control_wr_fd) {
          r = write(timer_manager_control_wr_fd, &byte, 1);
          if (r == -1) { sysErrorBelch("ioManagerDie: write"); }
          timer_manager_control_wr_fd = -1;
      }
  
      for (i=0; i < n_capabilities; i++) {
          fd = capabilities[i]->io_manager_control_wr_fd;
          if (0 <= fd) {
              r = write(fd, &byte, 1);
              if (r == -1) { sysErrorBelch("ioManagerDie: write"); }
              capabilities[i]->io_manager_control_wr_fd = -1;
          }
      }
  }
  
  void
  ioManagerStartCap (Capability **cap)
  {
      rts_evalIO(cap,&base_GHCziConcziIO_ensureIOManagerIsRunning_closure,NULL);
  }
  
  void
  ioManagerStart (void)
  {
      // Make sure the IO manager thread is running
      Capability *cap;
      if (timer_manager_control_wr_fd < 0 || io_manager_wakeup_fd < 0) {
          cap = rts_lock();
          ioManagerStartCap(&cap);
          rts_unlock(cap);
      }
  }
  #endif
  
  #if !defined(THREADED_RTS)
  
  #define N_PENDING_HANDLERS 16
  
  siginfo_t pending_handler_buf[N_PENDING_HANDLERS];
  siginfo_t *next_pending_handler = pending_handler_buf;
  
  #endif /* THREADED_RTS */
  
  /* -----------------------------------------------------------------------------
   * Low-level signal handler
   *
   * Places the requested handler on a stack of pending handlers to be
   * started up at the next context switch.
   * -------------------------------------------------------------------------- */
  
  static void
  generic_handler(int sig USED_IF_THREADS,
                  siginfo_t *info,
                  void *p STG_UNUSED)
  {
  #if defined(THREADED_RTS)
  
      StgWord8 buf[sizeof(siginfo_t) + 1];
      int r;
  
      buf[0] = sig;
      if (info == NULL) {
          // info may be NULL on Solaris (see #3790)
          memset(buf+1, 0, sizeof(siginfo_t));
      } else {
          memcpy(buf+1, info, sizeof(siginfo_t));
      }
  
      if (0 <= timer_manager_control_wr_fd)
      {
          r = write(timer_manager_control_wr_fd, buf, sizeof(siginfo_t)+1);
          if (r == -1 && errno == EAGAIN) {
              errorBelch("lost signal due to full pipe: %d\n", sig);
          }
      }
  
      nat i;
      int fd;
      for (i=0; i < n_capabilities; i++) {
          fd = capabilities[i]->io_manager_control_wr_fd;
          if (0 <= fd) {
              r = write(fd, buf, sizeof(siginfo_t)+1);
              if (r == -1 && errno == EAGAIN) {
                  errorBelch("lost signal due to full pipe: %d\n", sig);
              }
          }
      }
  
      // If the IO manager hasn't told us what the FD of the write end
      // of its pipe is, there's not much we can do here, so just ignore
      // the signal..
  
  #else /* not THREADED_RTS */
  
      /* Can't call allocate from here.  Probably can't call malloc
         either.  However, we have to schedule a new thread somehow.
  
         It's probably ok to request a context switch and allow the
         scheduler to  start the handler thread, but how do we
         communicate this to the scheduler?
  
         We need some kind of locking, but with low overhead (i.e. no
         blocking signals every time around the scheduler).
  
         Signal Handlers are atomic (i.e. they can't be interrupted), and
         we can make use of this.  We just need to make sure the
         critical section of the scheduler can't be interrupted - the
         only way to do this is to block signals.  However, we can lower
         the overhead by only blocking signals when there are any
         handlers to run, i.e. the set of pending handlers is
         non-empty.
      */
  
      /* We use a stack to store the pending signals.  We can't
         dynamically grow this since we can't allocate any memory from
         within a signal handler.
  
         Hence unfortunately we have to bomb out if the buffer
         overflows.  It might be acceptable to carry on in certain
         circumstances, depending on the signal.
      */
  
      memcpy(next_pending_handler, info, sizeof(siginfo_t));
  
      next_pending_handler++;
  
      // stack full?
      if (next_pending_handler == &pending_handler_buf[N_PENDING_HANDLERS]) {
          errorBelch("too many pending signals");
          stg_exit(EXIT_FAILURE);
      }
  
      interruptCapability(&MainCapability);
  
  #endif /* THREADED_RTS */
  }
  
  /* -----------------------------------------------------------------------------
   * Blocking/Unblocking of the user signals
   * -------------------------------------------------------------------------- */
  
  void
  blockUserSignals(void)
  {
      sigprocmask(SIG_BLOCK, &userSignals, &savedSignals);
  }
  
  void
  unblockUserSignals(void)
  {
      sigprocmask(SIG_SETMASK, &savedSignals, NULL);
  }
  
  rtsBool
  anyUserHandlers(void)
  {
      return n_haskell_handlers != 0;
  }
  
  #if !defined(THREADED_RTS)
  void
  awaitUserSignals(void)
  {
      while (!signals_pending() && sched_state == SCHED_RUNNING) {
          pause();
      }
  }
  #endif
  
  /* -----------------------------------------------------------------------------
   * Install a Haskell signal handler.
   *
   * We should really do this in Haskell in GHC.Conc, and share the
   * signal_handlers array with the one there.
   *
   * -------------------------------------------------------------------------- */
  
  int
  stg_sig_install(int sig, int spi, void *mask)
  {
      sigset_t signals, osignals;
      struct sigaction action;
      StgInt previous_spi;
  
      ACQUIRE_LOCK(&sig_mutex);
  
      // Block the signal until we figure out what to do
      // Count on this to fail if the signal number is invalid
      if (sig < 0 ||
            sigemptyset(&signals) ||
            sigaddset(&signals, sig) ||
            sigprocmask(SIG_BLOCK, &signals, &osignals)) {
          RELEASE_LOCK(&sig_mutex);
          return STG_SIG_ERR;
      }
  
      more_handlers(sig);
  
      previous_spi = signal_handlers[sig];
  
      action.sa_flags = 0;
  
      switch(spi) {
      case STG_SIG_IGN:
          action.sa_handler = SIG_IGN;
          break;
  
      case STG_SIG_DFL:
          action.sa_handler = SIG_DFL;
          break;
  
      case STG_SIG_RST:
          action.sa_flags |= SA_RESETHAND;
          /* fall through */
      case STG_SIG_HAN:
          action.sa_sigaction = generic_handler;
          action.sa_flags |= SA_SIGINFO;
          break;
  
      default:
          barf("stg_sig_install: bad spi");
      }
  
      if (mask != NULL)
          action.sa_mask = *(sigset_t *)mask;
      else
          sigemptyset(&action.sa_mask);
  
      action.sa_flags |= sig == SIGCHLD && nocldstop ? SA_NOCLDSTOP : 0;
  
      if (sigaction(sig, &action, NULL))
      {
          errorBelch("sigaction");
          RELEASE_LOCK(&sig_mutex);
          return STG_SIG_ERR;
      }
  
      signal_handlers[sig] = spi;
  
      switch(spi) {
      case STG_SIG_RST:
      case STG_SIG_HAN:
          sigaddset(&userSignals, sig);
          if (previous_spi != STG_SIG_HAN && previous_spi != STG_SIG_RST) {
              n_haskell_handlers++;
          }
          break;
  
      default:
          sigdelset(&userSignals, sig);
          if (previous_spi == STG_SIG_HAN || previous_spi == STG_SIG_RST) {
              n_haskell_handlers--;
          }
          break;
      }
  
      if (sigprocmask(SIG_SETMASK, &osignals, NULL))
      {
          errorBelch("sigprocmask");
          RELEASE_LOCK(&sig_mutex);
          return STG_SIG_ERR;
      }
  
      RELEASE_LOCK(&sig_mutex);
      return previous_spi;
  }
  
  /* -----------------------------------------------------------------------------
   * Creating new threads for signal handlers.
   * -------------------------------------------------------------------------- */
  
  #if !defined(THREADED_RTS)
  void
  startSignalHandlers(Capability *cap)
  {
    siginfo_t *info;
    int sig;
  
    blockUserSignals();
  
    while (next_pending_handler != pending_handler_buf) {
  
      next_pending_handler--;
  
      sig = next_pending_handler->si_signo;
      if (signal_handlers[sig] == STG_SIG_DFL) {
          continue; // handler has been changed.
      }
  
      info = stgMallocBytes(sizeof(siginfo_t), "startSignalHandlers");
             // freed by runHandler
      memcpy(info, next_pending_handler, sizeof(siginfo_t));
  
      scheduleThread(cap,
          createIOThread(cap,
            RtsFlags.GcFlags.initialStkSize,
                rts_apply(cap,
                    rts_apply(cap,
                        &base_GHCziConcziSignal_runHandlersPtr_closure,
                        rts_mkPtr(cap, info)),
                    rts_mkInt(cap, info->si_signo))));
    }
  
    unblockUserSignals();
  }
  #endif
  
  /* ----------------------------------------------------------------------------
   * Mark signal handlers during GC.
   * -------------------------------------------------------------------------- */
  
  void
  markSignalHandlers (evac_fn evac STG_UNUSED, void *user STG_UNUSED)
  {
      // nothing to do
  }
  
  #else /* !RTS_USER_SIGNALS */
  StgInt
  stg_sig_install(StgInt sig STG_UNUSED,
                  StgInt spi STG_UNUSED,
                  void* mask STG_UNUSED)
  {
    //barf("User signals not supported");
    return STG_SIG_DFL;
  }
  
  #endif
  
  #if defined(RTS_USER_SIGNALS)
  /* -----------------------------------------------------------------------------
   * SIGINT handler.
   *
   * We like to shutdown nicely after receiving a SIGINT, write out the
   * stats, write profiling info, close open files and flush buffers etc.
   * -------------------------------------------------------------------------- */
  static void
  shutdown_handler(int sig STG_UNUSED)
  {
      // If we're already trying to interrupt the RTS, terminate with
      // extreme prejudice.  So the first ^C tries to exit the program
      // cleanly, and the second one just kills it.
      if (sched_state >= SCHED_INTERRUPTING) {
          stg_exit(EXIT_INTERRUPTED);
      } else {
          interruptStgRts();
      }
  }
  
  /* -----------------------------------------------------------------------------
   * An empty signal handler, currently used for SIGPIPE
   * -------------------------------------------------------------------------- */
  static void
  empty_handler (int sig STG_UNUSED)
  {
      // nothing
  }
  
  /* -----------------------------------------------------------------------------
     SIGTSTP handling
  
     When a process is suspeended with ^Z and resumed again, the shell
     makes no attempt to save and restore the terminal settings.  So on
     resume, any terminal setting modificaions we made (e.g. turning off
     ICANON due to hSetBuffering NoBuffering) may well be lost.  Hence,
     we arrange to save and restore the terminal settings ourselves.
  
     The trick we use is:
       - catch SIGTSTP
       - in the handler,  kill(getpid(),SIGSTOP)
       - when this returns, restore the TTY settings
     This means we don't have to catch SIGCONT too.
  
     Note we don't re-throw SIGTSTP, we throw SIGSTOP instead.  This is
     for a few reasons:
  
        - re-throwing SIGTSTP would require temporarily restoring the
          default sigaction.
  
        - it doesn't work on certain buggy pthread implementations
          (e.g. OpenBSD).
  
        - throwing SIGTSTP seems slightly dodgy anyway.
  
     -------------------------------------------------------------------------- */
  
  static void sigtstp_handler(int sig);
  static void set_sigtstp_action (rtsBool handle);
  
  static void
  sigtstp_handler (int sig STG_UNUSED)
  {
      int fd;
      struct termios ts[3];
  
      // save the current TTY state for TTYs we modified
      for (fd = 0; fd <= 2; fd++) {
          if (__hscore_get_saved_termios(fd) != NULL) {
              tcgetattr(fd,&ts[fd]);
          }
      }
  
      // really stop the process now
      kill(getpid(), SIGSTOP);
  
      // on return, restore the TTY state
      for (fd = 0; fd <= 2; fd++) {
          if (__hscore_get_saved_termios(fd) != NULL) {
              tcsetattr(0,TCSANOW,&ts[fd]);
          }
      }
  }
  
  static void
  set_sigtstp_action (rtsBool handle)
  {
      struct sigaction sa;
      if (handle) {
          sa.sa_handler = sigtstp_handler;
      } else {
          sa.sa_handler = SIG_DFL;
      }
      sa.sa_flags = 0;
      sigemptyset(&sa.sa_mask);
      if (sigaction(SIGTSTP, &sa, NULL) != 0) {
          sysErrorBelch("warning: failed to install SIGTSTP handler");
      }
  }
  
  /* -----------------------------------------------------------------------------
   * Install default signal handlers.
   *
   * The RTS installs a default signal handler for catching
   * SIGINT, so that we can perform an orderly shutdown.
   *
   * Haskell code may install their own SIGINT handler, which is
   * fine, provided they're so kind as to put back the old one
   * when they de-install.
   *
   * In addition to handling SIGINT, the RTS also handles SIGFPE
   * by ignoring it.  Apparently IEEE requires floating-point
   * exceptions to be ignored by default, but alpha-dec-osf3
   * doesn't seem to do so.
   * -------------------------------------------------------------------------- */
  void
  initDefaultHandlers(void)
  {
      struct sigaction action,oact;
  
      // install the SIGINT handler
      action.sa_handler = shutdown_handler;
      sigemptyset(&action.sa_mask);
      action.sa_flags = 0;
      if (sigaction(SIGINT, &action, &oact) != 0) {
          sysErrorBelch("warning: failed to install SIGINT handler");
      }
  
  #if defined(HAVE_SIGINTERRUPT)
      siginterrupt(SIGINT, 1);    // isn't this the default? --SDM
  #endif
  
      // install the SIGFPE handler
  
      // In addition to handling SIGINT, also handle SIGFPE by ignoring it.
      // Apparently IEEE requires floating-point exceptions to be ignored by
      // default, but alpha-dec-osf3 doesn't seem to do so.
  
      // Commented out by SDM 2/7/2002: this causes an infinite loop on
      // some architectures when an integer division by zero occurs: we
      // don't recover from the floating point exception, and the
      // program just generates another one immediately.
  #if 0
      action.sa_handler = SIG_IGN;
      sigemptyset(&action.sa_mask);
      action.sa_flags = 0;
      if (sigaction(SIGFPE, &action, &oact) != 0) {
          sysErrorBelch("warning: failed to install SIGFPE handler");
      }
  #endif
  
  #ifdef alpha_HOST_ARCH
      ieee_set_fp_control(0);
  #endif
  
      // ignore SIGPIPE; see #1619
      // actually, we use an empty signal handler rather than SIG_IGN,
      // so that SIGPIPE gets reset to its default behaviour on exec.
      action.sa_handler = empty_handler;
      sigemptyset(&action.sa_mask);
      action.sa_flags = 0;
      if (sigaction(SIGPIPE, &action, &oact) != 0) {
          sysErrorBelch("warning: failed to install SIGPIPE handler");
      }
  
      set_sigtstp_action(rtsTrue);
  }
  
  void
  resetDefaultHandlers(void)
  {
      struct sigaction action;
  
      action.sa_handler = SIG_DFL;
      sigemptyset(&action.sa_mask);
      action.sa_flags = 0;
  
      // restore SIGINT
      if (sigaction(SIGINT, &action, NULL) != 0) {
          sysErrorBelch("warning: failed to uninstall SIGINT handler");
      }
      // restore SIGPIPE
      if (sigaction(SIGPIPE, &action, NULL) != 0) {
          sysErrorBelch("warning: failed to uninstall SIGPIPE handler");
      }
  
      set_sigtstp_action(rtsFalse);
  }
  
  #endif /* RTS_USER_SIGNALS */
  