[pf3gnuchains/sourceware.git] / winsup / cygwin / sigproc.cc

/* sigproc.cc: inter/intra signal and sub process handler

   Copyright 1997, 1998, 1999, 2000 Cygnus Solutions.

   Written by Christopher Faylor <cgf@cygnus.com>

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#include <stdlib.h>
#include <time.h>
#include <sys/wait.h>
#include <errno.h>
#include <stdlib.h>
#include "winsup.h"
#include "sync.h"

extern BOOL allow_ntsec;

/*
 * Convenience defines
 */
#define WSSC               60000 // Wait for signal completion
#define WPSP               40000 // Wait for proc_subproc mutex
#define WSPX               20000 // Wait for wait_sig to terminate
#define WWSP               20000 // Wait for wait_subproc to terminate

#define WAIT_SIG_PRIORITY               THREAD_PRIORITY_NORMAL

#define TOTSIGS (NSIG + __SIGOFFSET)

#define sip_printf(fmt, args...) sigproc_printf (fmt , ## args)

#define wake_wait_subproc() SetEvent (events[0])

#define no_signals_available() (!hwait_sig || !sig_loop_wait)

/*
 * Global variables
 */
const char *__sp_fn ;
int __sp_ln;

char NO_COPY myself_nowait_dummy[1] = {'0'};// Flag to sig_send that signal goes to
                                        //  current process but no wait is required
char NO_COPY myself_nowait_nonmain_dummy[1] = {'1'};// Flag to sig_send that signal goes to
                                        //  current process but no wait is required
                                        //  if this is not the main thread.

HANDLE NO_COPY signal_arrived;          // Event signaled when a signal has
                                        //  resulted in a user-specified
                                        //  function call
/*
 * Common variables
 */


/* How long to wait for message/signals.  Normally this is infinite.
 * On termination, however, these are set to zero as a flag to exit.
 */

#define Static static NO_COPY

Static DWORD proc_loop_wait = 500;      // Wait for subprocesses to exit
Static DWORD sig_loop_wait = 500;       // Wait for signals to arrive

Static HANDLE sigcatch_nonmain = NULL;  // The semaphore signaled when
                                        //  signals are available for
                                        //  processing from non-main thread
Static HANDLE sigcatch_main = NULL;     // Signalled when main thread sends a
                                        //  signal
Static HANDLE sigcatch_nosync = NULL;   // Signal wait_sig to scan sigtodo
                                        //  but not to bother with any
                                        //  synchronization
Static HANDLE sigcomplete_main = NULL;  // Event signaled when a signal has
                                        //  finished processing for the main
                                        //  thread
Static HANDLE sigcomplete_nonmain = NULL;// Semaphore raised for non-main
                                        //  threads when a signal has finished
                                        //  processing
Static HANDLE hwait_sig = NULL;         // Handle of wait_sig thread
Static HANDLE hwait_subproc = NULL;     // Handle of sig_subproc thread

Static HANDLE wait_sig_inited = NULL;   // Control synchronization of
                                        //  message queue startup

/* Used by WaitForMultipleObjects.  These are handles to child processes.
 */
Static HANDLE events[PSIZE + 1] = {0};  // All my children's handles++
#define hchildren (events + 1)          // Where the children handles begin
Static pinfo *pchildren[PSIZE] = {NULL};// All my children info
Static pinfo *zombies[PSIZE] = {NULL};  // All my deceased children info
Static int nchildren = 0;               // Number of active children
Static int nzombies = 0;                // Number of deceased children

Static waitq waitq_head = {0, 0, 0, 0, 0, 0, 0};// Start of queue for wait'ing threads
Static waitq waitq_main;                // Storage for main thread

muto NO_COPY *sync_proc_subproc = NULL; // Control access to subproc stuff

DWORD NO_COPY maintid = 0;              // ID of the main thread
DWORD NO_COPY sigtid = 0;               // ID of the signal thread

int NO_COPY pending_signals = 0;        // TRUE if signals pending

/* Functions
 */
static int __stdcall checkstate (waitq *);
static __inline__ BOOL get_proc_lock (DWORD, DWORD);
static HANDLE __stdcall getsem (pinfo *, const char *, int, int);
static void __stdcall remove_child (int);
static void __stdcall remove_zombie (int);
static DWORD WINAPI wait_sig (VOID *arg);
static int __stdcall stopped_or_terminated (waitq *, pinfo *);
static DWORD WINAPI wait_subproc (VOID *);

/* Determine if the parent process is alive.
 */

BOOL __stdcall
my_parent_is_alive ()
{
  DWORD res;
  if (!parent_alive)
    {
      debug_printf ("No parent_alive mutex");
      res = FALSE;
    }
  else
    for (int i = 0; i < 2; i++)
      switch (res = WaitForSingleObject (parent_alive, 0))
        {
          case WAIT_OBJECT_0:
            debug_printf ("parent dead.");
            res = FALSE;
            goto out;
          case WAIT_TIMEOUT:
            debug_printf ("parent still alive");
            res = TRUE;
            goto out;
          case WAIT_FAILED:
            DWORD werr = GetLastError ();
            if (werr == ERROR_INVALID_HANDLE && i == 0)
              continue;
            system_printf ("WFSO for parent_alive(%p) failed, error %d",
                           parent_alive, werr);
            res = FALSE;
            goto out;
        }
out:
  return res;
}

__inline static void
wait_for_me ()
{
  /* See if this is the first signal call after initialization.
   * If so, wait for notification that all initialization has completed.
   * Then set the handle to NULL to avoid checking this again.
   */
  if (wait_sig_inited)
    {
      (void) WaitForSingleObject (wait_sig_inited, INFINITE);
      (void) ForceCloseHandle (wait_sig_inited);
      wait_sig_inited = NULL;
    }
}

static BOOL __stdcall
proc_can_be_signalled (pinfo *p)
{
  if (p == myself_nowait || p == myself_nowait_nonmain || p == myself)
    {
      wait_for_me ();
      return 1;
    }

  return ISSTATE (p, PID_INITIALIZING) ||
         (((p)->process_state & (PID_ACTIVE | PID_IN_USE)) ==
          (PID_ACTIVE | PID_IN_USE));
}

/* Test to determine if a process really exists and is processing
 * signals.
 */
BOOL __stdcall
proc_exists (pinfo *p)
{
  HANDLE h;

  if (p == NULL)
    return FALSE;

  if (p == myself || p == myself_nowait_nonmain || p == myself_nowait)
    return TRUE;

  if (p->process_state == PID_NOT_IN_USE || !p->dwProcessId)
    return FALSE;

  sip_printf ("checking for existence of pid %d, window pid %d", p->pid,
              p->dwProcessId);
  if (p->ppid == myself->pid && p->hProcess != NULL)
    {
      sip_printf ("it's mine, process_state %x", p->process_state);
      return proc_can_be_signalled (p);
    }

  /* Note: Process is alive if OpenProcess() call fails due to permissions */
  if (((h = OpenProcess (STANDARD_RIGHTS_REQUIRED, FALSE, p->dwProcessId))
      != NULL) || (GetLastError () == ERROR_ACCESS_DENIED))
    {
      sip_printf ("it exists, %p", h);
      if (h)
        {
          DWORD rc = WaitForSingleObject (h, 0);
          CloseHandle (h);
          if (rc == WAIT_OBJECT_0)
            return 0;
        }
      return proc_can_be_signalled (p);
    }

  sip_printf ("it doesn't exist");
  /* If the parent pid does not exist, clean this process out of the pinfo
   * table.  It must have died abnormally.
   */
  if ((p->pid == p->ppid) || (p->ppid == 1) || !proc_exists (procinfo (p->ppid)))
    {
      p->hProcess = NULL;
      p->process_state = PID_NOT_IN_USE;
    }
  return FALSE;
}

/* Handle all subprocess requests
 */
#define vchild ((pinfo *) val)
int __stdcall
proc_subproc (DWORD what, DWORD val)
{
  int rc = 1;
  int potential_match;
  DWORD exitcode;
  pinfo *child;
  int clearing;
  waitq *w;

#define wval     ((waitq *) val)

  sip_printf ("args: %x, %d", what, val);

  if (!get_proc_lock (what, val))       // Serialize access to this function
    {
      sip_printf ("I am not ready");
      goto out1;
    }

  switch (what)
    {
    /* Add a new subprocess to the children arrays.
     * (usually called from the main thread)
     */
    case PROC_ADDCHILD:
      if (nchildren >= PSIZE - 1)
        system_printf ("nchildren too large %d", nchildren);
      if (WaitForSingleObject (vchild->hProcess, 0) != WAIT_TIMEOUT)
        {
          system_printf ("invalid process handle %p.  pid %d, win pid %d",
                        vchild->hProcess, vchild->pid, vchild->dwProcessId);
          rc = 0;
          break;
        }

      pchildren[nchildren] = vchild;
      hchildren[nchildren] = vchild->hProcess;
      ProtectHandle (vchild->hProcess);
      sip_printf ("added pid %d to wait list, slot %d, winpid %p, handle %p",
                  vchild->pid, nchildren, vchild->dwProcessId,
                  vchild->hProcess);

      nchildren++;
      wake_wait_subproc ();
      break;

    /* A child process had terminated.
     * Possibly this is just due to an exec().  Cygwin implements an exec()
     * as a "handoff" from one windows process to another.  If child->hProcess
     * is different from what is recorded in hchildren, then this is an exec().
     * Otherwise this is a normal child termination event.
     * (called from wait_subproc thread)
     */
    case PROC_CHILDTERMINATED:
      rc = 0;
      child = pchildren[val];
      if (GetExitCodeProcess (hchildren[val], &exitcode) &&
          hchildren[val] != child->hProcess)
        {
          sip_printf ("pid %d[%d], reparented old hProcess %p, new %p",
                      child->pid, val, hchildren[val], child->hProcess);
          ForceCloseHandle1 (hchildren[val], childhProc);
          hchildren[val] = child->hProcess; /* Filled out by child */
          ProtectHandle1 (child->hProcess, childhProc);
          break;                        // This was an exec()
        }

      sip_printf ("pid %d[%d] terminated, handle %p, nchildren %d, nzombies %d",
                  child->pid, val, hchildren[val], nchildren, nzombies);
      remove_child (val);               // Remove from children arrays
      zombies[nzombies++] = child;      // Add to zombie array
      child->process_state = PID_ZOMBIE;// Walking dead
      if (!proc_loop_wait)              // Don't bother if wait_subproc is
        break;                          //  exiting

      /* Send a SIGCHLD to myself. */
      rc = sig_send (myself_nowait, SIGCHLD);   // Send a SIGCHLD
      break;

    /* A child is in the stopped state.  Scan wait() queue to see if anyone
     * should be notified.  (Called from wait_sig thread)
     */
    case PROC_CHILDSTOPPED:
      child = myself;           // Just to avoid accidental NULL dereference
      sip_printf ("Received stopped notification");
      clearing = 0;
      goto scan_wait;

    /* Clear all waiting threads.  Called from exceptions.cc prior to
     * the main thread's dispatch to a signal handler function.
     * (called from wait_sig thread)
     */
    case PROC_CLEARWAIT:
      /* Clear all "wait"ing threads. */
      if (val)
        sip_printf ("clear waiting threads");
      else
        sip_printf ("looking for processes to reap");
      clearing = val;

    scan_wait:
      /* Scan the linked list of wait()ing threads.  If a wait's parameters
       * match this pid, then activate it.
       */
      for (w = &waitq_head; w->next != NULL; w = w->next)
        {
          if ((potential_match = checkstate (w)) > 0)
            sip_printf ("released waiting thread");
          else if (!clearing && potential_match < 0)
            sip_printf ("only found non-terminated children");
          else if (potential_match <= 0)                // nothing matched
            {
              sip_printf ("waiting thread found no children");
              HANDLE oldw = w->next->ev;
              if (clearing)
                w->next->status = -1;           /* flag that a signal was received */
              else
                w->next->ev = NULL;
              if (!SetEvent (oldw))
                system_printf ("couldn't wake up wait event %p, %E", oldw);
              w->next = w->next->next;
            }
          if (w->next == NULL)
            break;
        }

      if (!clearing)
        sip_printf ("finished processing terminated/stopped child");
      else
        {
          waitq_head.next = NULL;
          sip_printf ("finished clearing");
        }
      break;

    /* Handle a wait4() operation.  Allocates an event for the calling
     * thread which is signaled when the appropriate pid exits or stops.
     * (usually called from the main thread)
     */
    case PROC_WAIT:
      wval->ev = NULL;          // Don't know event flag yet

      if (wval->pid <= 0)
        child = NULL;           // Not looking for a specific pid
      else if ((child = procinfo (wval->pid)) == NULL)
        goto out;               // invalid pid.  flag no such child

      wval->status = 0;         // Don't know status yet

      /* Put waitq structure at the end of a linked list. */
      for (w = &waitq_head; w->next != NULL; w = w->next)
        if (w->next == wval && (w->next = w->next->next) == NULL)
          break;

      wval->next = NULL;        /* This will be last in the list */
      sip_printf ("wval->pid %d, wval->options %d", wval->pid, wval->options);

      /* If the first time for this thread, create a new event, otherwise
       * reset the event.
       */
      if ((wval->ev = wval->thread_ev) == NULL)
        {
          wval->ev = wval->thread_ev = CreateEvent (&sec_none_nih, TRUE,
                                                    FALSE, NULL);
          ProtectHandle (wval->ev);
        }
      ResetEvent (wval->ev);

      /* Scan list of children to see if any have died.
       * If so, the event flag is set so that the wait* ()
       * process will return immediately.
       *
       * If no children were found and the wait option was WNOHANG,
       * then set the pid to 0 and remove the waitq value from
       * consideration.
       */
      w->next = wval;           /* set at end of wait queue */
      if ((potential_match = checkstate (w)) <= 0)
        {
          if (!potential_match)
            {
              w->next = NULL;           // don't want to keep looking
              wval->ev = NULL;          // flag that there are no children
              sip_printf ("no appropriate children, %p, %p",
                          wval->thread_ev, wval->ev);
            }
          else if (wval->options & WNOHANG)
            {
              w->next = NULL;           // don't want to keep looking
              wval->pid = 0;            // didn't find a pid
              if (!SetEvent (wval->ev)) // wake up wait4 () immediately
                system_printf ("Couldn't wake up wait event, %E");
              sip_printf ("WNOHANG and no terminated children, %p, %p",
                          wval->thread_ev, wval->ev);
            }
        }
      if (w->next != NULL)
        sip_printf ("wait activated %p, %p", wval->thread_ev, wval->ev);
      else if (wval->ev != NULL)
        sip_printf ("wait activated %p.  Reaped zombie.", wval->ev);
      else
        sip_printf ("wait not activated %p, %p", wval->thread_ev, wval->ev);
      break;
  }

out:
  sync_proc_subproc->release ();        // Release the lock
out1:
  sip_printf ("returning %d", rc);
  return rc;
}

/* Terminate the wait_subproc thread.
 * Called on process exit.
 * Also called by spawn_guts to disassociate any subprocesses from this
 * process.  Subprocesses will then know to clean up after themselves and
 * will not become zombies.
 */
void __stdcall
proc_terminate (void)
{
  sip_printf ("nchildren %d, nzombies %d", nchildren, nzombies);
  /* Signal processing is assumed to be blocked in this routine. */
  if (hwait_subproc)
    {
      int rc;
      proc_loop_wait = 0;       // Tell wait_subproc thread to exit
      wake_wait_subproc ();     // Wake wait_subproc loop

      /* Wait for wait_subproc thread to exit (but not *too* long) */
      if ((rc = WaitForSingleObject (hwait_subproc, WWSP)) != WAIT_OBJECT_0)
        if (rc == WAIT_TIMEOUT)
          system_printf ("WFSO(hwait_subproc) timed out");
        else
          system_printf ("WFSO(hwait_subproc), rc %d, %E", rc);

      HANDLE h = hwait_subproc;
      hwait_subproc = NULL;
      ForceCloseHandle1 (h, hwait_subproc);

      sync_proc_subproc->acquire(WPSP);
      (void) proc_subproc (PROC_CLEARWAIT, 1);

      lock_pinfo_for_update (INFINITE);
      /* Clean out zombie processes from the pid list. */
      int i;
      for (i = 0; i < nzombies; i++)
        {
          pinfo *child;
          if ((child = zombies[i])->hProcess)
            {
              ForceCloseHandle1 (child->hProcess, childhProc);
              child->hProcess = NULL;
            }
          child->process_state = PID_NOT_IN_USE;
        }

      /* Disassociate my subprocesses */
      for (i = 0; i < nchildren; i++)
        {
          pinfo *child;
          if ((child = pchildren[i])->process_state == PID_NOT_IN_USE)
            continue;           // Should never happen
          if (!child->hProcess)
            sip_printf ("%d(%d) hProcess cleared already?", child->pid,
                        child->dwProcessId);
          else
            {
              ForceCloseHandle1 (child->hProcess, childhProc);
              child->hProcess = NULL;
              if (!proc_exists (child))
                {
                  sip_printf ("%d(%d) doesn't exist", child->pid,
                              child->dwProcessId);
                  child->process_state = PID_NOT_IN_USE;        /* a reaped child */
                }
              else
                {
                  sip_printf ("%d(%d) closing active child handle", child->pid,
                              child->dwProcessId);
                  child->ppid = 1;
                  if (child->pgid == myself->pid)
                    child->process_state |= PID_ORPHANED;
                }
            }
        }
      unlock_pinfo ();
      nchildren = nzombies = 0;

      /* Attempt to close and release sync_proc_subproc in a
       * non-raceable manner.
       */
      muto *m = sync_proc_subproc;
      if (m)
        {
          sync_proc_subproc = NULL;
          delete m;
        }
    }
  sip_printf ("leaving");
}

/* Clear pending signal from the sigtodo array
 */
void __stdcall
sig_clear (int sig)
{
  (void) InterlockedExchange (myself->getsigtodo(sig), 0L);
  return;
}

/* Force the wait_sig thread to wake up and scan the sigtodo array.
 */
extern "C" int __stdcall
sig_dispatch_pending (int justwake)
{
  if (!hwait_sig)
    return 0;

  int was_pending = pending_signals;
#ifdef DEBUGGING
  sip_printf ("pending_signals %d", was_pending);
#endif
  if (!was_pending && !justwake)
#ifdef DEBUGGING
    sip_printf ("no need to wake anything up");
#else
    ;
#endif
  else
    {
      wait_for_me ();
      if (!justwake)
        (void) sig_send (myself, __SIGFLUSH);
      else if (ReleaseSemaphore (sigcatch_nosync, 1, NULL))
#ifdef DEBUGGING
        sip_printf ("woke up wait_sig");
#else
        ;
#endif
      else if (no_signals_available ())
        /*sip_printf ("I'm going away now")*/;
      else
        system_printf ("%E releasing sigcatch_nosync(%p)", sigcatch_nosync);
 
    }
  return was_pending;
}

/* Message initialization.  Called from dll_crt0_1
 *
 * This routine starts the signal handling thread.  The wait_sig_inited
 * event is used to signal that the thread is ready to handle signals.
 * We don't wait for this during initialization but instead detect it
 * in sig_send to gain a little concurrency.
 */
void __stdcall
sigproc_init ()
{
  wait_sig_inited = CreateEvent (&sec_none_nih, FALSE, FALSE, NULL);
  ProtectHandle (wait_sig_inited);

  /* local event signaled when main thread has been dispatched
     to a signal handler function. */
  signal_arrived = CreateEvent(&sec_none_nih, TRUE, FALSE, NULL);

  maintid = GetCurrentThreadId ();// For use in determining if signals
                                  //  should be blocked.

  if (!(hwait_sig = makethread (wait_sig, NULL, 0, "sig")))
    {
      system_printf ("cannot create wait_sig thread, %E");
      api_fatal ("terminating");
    }

  ProtectHandle (hwait_sig);

  /* sync_proc_subproc is used by proc_subproc.  It serialises
   * access to the children and zombie arrays.
   */
  sync_proc_subproc = new_muto (FALSE, "sync_proc_subproc");

  /* Initialize waitq structure for main thread.  A waitq structure is
   * allocated for each thread that executes a wait to allow multiple threads
   * to perform waits.  Pre-allocate a waitq structure for the main thread.
   */
  waitq *w;
  if ((w = (waitq *)waitq_storage.get ()) == NULL)
    {
      w = &waitq_main;
      waitq_storage.set (w);
    }
  memset (w, 0, sizeof *w);     // Just to be safe

  sip_printf ("process/signal handling enabled(%x)", myself->process_state);
  return;
}

/* Called on process termination to terminate signal and process threads.
 */
void __stdcall
sigproc_terminate (void)
{
  HANDLE h = hwait_sig;
  hwait_sig = NULL;

  if (GetCurrentThreadId () == sigtid)
    {
      ForceCloseHandle (sigcomplete_main);
      for (int i = 0; i < 20; i++)
        (void) ReleaseSemaphore (sigcomplete_nonmain, 1, NULL);
      ForceCloseHandle (sigcomplete_nonmain);
      ForceCloseHandle (sigcatch_main);
      ForceCloseHandle (sigcatch_nonmain);
      ForceCloseHandle (sigcatch_nosync);
    }
  proc_terminate ();            // Terminate process handling thread

  if (!sig_loop_wait)
    sip_printf ("sigproc_terminate: sigproc handling not active");
  else
    {
      sigproc_printf ("entering");
      sig_loop_wait = 0;        // Tell wait_sig to exit when it is
                                //  finished with anything it is doing
      sig_dispatch_pending (TRUE);      // wake up and die

      /* If !hwait_sig, then the process probably hasn't even finished
       * its initialization phase.
       */
      if (hwait_sig)
        {
          if (GetCurrentThreadId () != sigtid)
            WaitForSingleObject (h, 10000);
          ForceCloseHandle1 (h, hwait_sig);

          /* Exiting thread.  Cleanup.  Don't set to inactive if a child has been
             execed with the same pid. */
          if (!myself->dwProcessId || myself->dwProcessId == GetCurrentProcessId ())
            myself->process_state &= ~PID_ACTIVE;
          else
            sip_printf ("Did not clear PID_ACTIVE since %d != %d",
                        myself->dwProcessId, GetCurrentProcessId ());

          /* In case of a sigsuspend */
          SetEvent (signal_arrived);

          if (GetCurrentThreadId () != sigtid)
            {
              ForceCloseHandle (sigcomplete_main);
              ForceCloseHandle (sigcomplete_nonmain);
              ForceCloseHandle (sigcatch_main);
              ForceCloseHandle (sigcatch_nonmain);
              ForceCloseHandle (sigcatch_nosync);
            }
        }
      sip_printf ("done");
    }

  /* Set this so that subsequent tests will succeed. */
  if (!myself->dwProcessId)
    myself->dwProcessId = GetCurrentProcessId ();

  return;
}

/* Send a signal to another process by raising its signal semaphore.
 * If pinfo *p == NULL, send to the current process.
 * If sending to this process, wait for notification that a signal has
 * completed before returning.
 */
int __stdcall
sig_send (pinfo *p, int sig, DWORD ebp)
{
  int rc = 1;
  DWORD tid = GetCurrentThreadId ();
  BOOL its_me;
  HANDLE thiscatch = NULL;
  HANDLE thiscomplete = NULL;
  BOOL wait_for_completion;
  extern signal_dispatch sigsave;

  if (p == myself_nowait_nonmain)
    p = (tid == maintid) ? myself : myself_nowait;
  if (!(its_me = (p == NULL || p == myself || p == myself_nowait)))
    wait_for_completion = FALSE;
  else
    {
      if (no_signals_available ())
        goto out;               // Either exiting or not yet initializing
      wait_for_me ();
      wait_for_completion = p != myself_nowait;
      p = myself;
    }

  /* It is possible that the process is not yet ready to receive messages
   * or that it has exited.  Detect this.
   */
  if (!proc_can_be_signalled (p))       /* Is the process accepting messages? */
    {
      sip_printf ("invalid pid %d(%x), signal %d",
                  p->pid, p->process_state, sig);
      set_errno (ESRCH);
      goto out;
    }

  sip_printf ("pid %d, signal %d, its_me %d", p->pid, sig, its_me);

  if (its_me)
    {
      if (!wait_for_completion)
        thiscatch = sigcatch_nosync;
      else if (tid != maintid)
        {
          thiscatch = sigcatch_nonmain;
          thiscomplete = sigcomplete_nonmain;
        }
      else
        {
          thiscatch = sigcatch_main;
          thiscomplete = sigcomplete_main;
          sigsave.ebp = ebp ?: (DWORD) __builtin_frame_address (1);
        }
    }
  else if (!(thiscatch = getsem (p, "sigcatch", 0, 0)))
    goto out;             // Couldn't get the semaphore.  getsem issued
                          //  an error, if appropriate.

#if WHEN_MULTI_THREAD_SIGNALS_WORK
  signal_dispatch *sd;
  sd = signal_dispatch_storage.get ();
  if (sd == NULL)
    sd = signal_dispatch_storage.create ();
#endif

  /* Increment the sigtodo array to signify which signal to assert.
   */
  (void) InterlockedIncrement (p->getsigtodo(sig));

  /* Notify the process that a signal has arrived.
   */
  SetLastError (0);

#if 0
  int prio;
  prio = GetThreadPriority (GetCurrentThread ());
  (void) SetThreadPriority (GetCurrentThread (), THREAD_PRIORITY_TIME_CRITICAL);
#endif

  if (!ReleaseSemaphore (thiscatch, 1, NULL) && (int) GetLastError () > 0)
    {
sigproc_printf ("ReleaseSemaphore failed, %E");
      /* Couldn't signal the semaphore.  This probably means that the
       * process is exiting.
       */
      if (!its_me)
        ForceCloseHandle (thiscatch);
      else
        {
          if (no_signals_available ())
            sip_printf ("I'm going away now");
          else if ((int) GetLastError () == -1)
            rc = WaitForSingleObject (thiscomplete, 500);
          else
            system_printf ("error sending signal %d to pid %d, semaphore %p, %E",
                          sig, p->pid, thiscatch);
        }
      goto out;
    }
sigproc_printf ("ReleaseSemaphore succeeded");

  /* No need to wait for signal completion unless this was a signal to
   * this process.
   *
   * If it was a signal to this process, wait for a dispatched signal.
   * Otherwise just wait for the wait_sig to signal that it has finished
   * processing the signal.
   */
  if (!wait_for_completion)
    {
      rc = WAIT_OBJECT_0;
      sip_printf ("Not waiting for sigcomplete.  its_me %d sig %d", its_me, sig);
      if (!its_me)
        ForceCloseHandle (thiscatch);
    }
  else
    {
      sip_printf ("Waiting for thiscomplete %p", thiscomplete);

      SetLastError (0);
      rc = WaitForSingleObject (thiscomplete, WSSC);
      /* Check for strangeness due to this thread being redirected by the
         signal handler.  Sometimes a WAIT_TIMEOUT will occur when the
         thread hasn't really timed out.  So, check again.
         FIXME: This isn't foolproof. */
      if (rc != WAIT_OBJECT_0 &&
          WaitForSingleObject (thiscomplete, 0) == WAIT_OBJECT_0)
        rc = WAIT_OBJECT_0;
    }

#if 0
  SetThreadPriority (GetCurrentThread (), prio);
#endif

  if (rc == WAIT_OBJECT_0)
    rc = 0;             // Successful exit
  else
    {
      /* It's an error unless sig_loop_wait == 0 (the process is exiting). */
      if (!no_signals_available ())
        system_printf ("wait for sig_complete event failed, sig %d, rc %d, %E",
                      sig, rc);
      set_errno (ENOSYS);
      rc = -1;
    }

out:
  sip_printf ("returning %d from sending signal %d", rc, sig);
  return rc;
}

/* Set pending signal from the sigtodo array
 */
void __stdcall
sig_set_pending (int sig)
{
  (void) InterlockedIncrement (myself->getsigtodo(sig));
  return;
}

/* Initialize the wait_subproc thread.
 * Called from fork() or spawn() to initialize the handling of subprocesses.
 */
void __stdcall
subproc_init (void)
{
  if (hwait_subproc)
    return;

  /* A "wakeup" handle which can be toggled to make wait_subproc reexamine
   * the hchildren array.
   */
  events[0] = CreateEvent (&sec_none_nih, FALSE, FALSE, NULL);
  if (!(hwait_subproc = makethread (wait_subproc, NULL, 0, "+proc")))
    system_printf ("cannot create wait_subproc thread, %E");
  ProtectHandle (events[0]);
  ProtectHandle (hwait_subproc);
  sip_printf ("started wait_subproc thread %p", hwait_subproc);
}

/* Initialize some of the memory block passed to child processes
   by fork/spawn/exec. */

void __stdcall
init_child_info (DWORD chtype, child_info *ch, int pid, HANDLE subproc_ready)
{
  subproc_init ();
  memset (ch, 0, sizeof *ch);
  ch->cb = sizeof *ch;
  ch->type = chtype;
  ch->cygpid = pid;
  ch->shared_h = cygwin_shared_h;
  ch->console_h = console_shared_h;
  ch->subproc_ready = subproc_ready;
  if (chtype != PROC_EXEC || !parent_alive)
    ch->parent_alive = hwait_subproc;
  else if (parent_alive)
    DuplicateHandle (hMainProc, parent_alive, hMainProc, &ch->parent_alive,
                     0, 1, DUPLICATE_SAME_ACCESS);
}

/* Check the state of all of our children to see if any are stopped or
 * terminated.
 */
static int __stdcall
checkstate (waitq *w)
{
  int i, x, potential_match = 0;
  pinfo *child;

  sip_printf ("nchildren %d, nzombies %d", nchildren, nzombies);

  /* Check already dead processes first to see if they match the criteria
   * given in w->next.
   */
  for (i = 0; i < nzombies; i++)
    if ((x = stopped_or_terminated (w, child = zombies[i])) < 0)
      potential_match = -1;
    else if (x > 0)
      {
        remove_zombie (i);
        potential_match = 1;
        goto out;
      }

  sip_printf ("checking alive children");

  /* No dead terminated children matched.  Check for stopped children. */
  for (i = 0; i < nchildren; i++)
    if ((x = stopped_or_terminated (w, pchildren[i])) < 0)
      potential_match = -1;
    else if (x > 0)
      {
        potential_match = 1;
        break;
      }

out:
  sip_printf ("returning %d", potential_match);
  return potential_match;
}

/* Get or create a process specific semaphore used in message passing.
 */
static HANDLE __stdcall
getsem (pinfo *p, const char *str, int init, int max)
{
  HANDLE h;

  if (p != NULL)
    {
      if (!proc_can_be_signalled (p))
        {
          set_errno (ESRCH);
          return NULL;
        }
      int wait = 10000;
      sip_printf ("pid %d, ppid %d, wait %d, initializing %x", p->pid, p->ppid, wait,
                  ISSTATE (p, PID_INITIALIZING));
      for (int i = 0; ISSTATE (p, PID_INITIALIZING) && i < wait; i++)
        Sleep (1);
    }

  SetLastError (0);
  if (p == NULL)
    {
      char sa_buf[1024];

      DWORD winpid = GetCurrentProcessId ();
      h = CreateSemaphore (allow_ntsec ? sec_user (sa_buf) : &sec_none_nih,
                           init, max, str = shared_name (str, winpid));
      p = myself;
    }
  else
    {
      h = OpenSemaphore (SEMAPHORE_ALL_ACCESS, FALSE,
                         str = shared_name (str, p->dwProcessId));

      if (h == NULL)
        {
          if (GetLastError () == ERROR_FILE_NOT_FOUND && !proc_exists (p))
            set_errno (ESRCH);
          else
            set_errno (EPERM);
          return NULL;
        }
    }

  if (!h)
    {
      system_printf ("can't %s %s, %E", p ? "open" : "create", str);
      set_errno (ESRCH);
    }
  return h;
}

/* Get the sync_proc_subproc muto to control access to
 * children, zombie arrays.
 * Attempt to handle case where process is exiting as we try to grab
 * the mutex.
 */
static __inline__ BOOL
get_proc_lock (DWORD what, DWORD val)
{
  Static int lastwhat = -1;
  if (!sync_proc_subproc)
    return FALSE;
  if (sync_proc_subproc->acquire (WPSP))
    {
      lastwhat = what;
      return TRUE;
    }
  if (!sync_proc_subproc)
    return FALSE;
  system_printf ("Couldn't aquire sync_proc_subproc for(%d,%d), %E, last %d",
                  what, val, lastwhat);
  return TRUE;
}

/* Remove a child from pchildren/hchildren by swapping it with the
 * last child in the list.
 */
static void __stdcall
remove_child (int ci)
{
  sip_printf ("removing [%d], pid %d, handle %p, nchildren %d",
              ci, pchildren[ci]->pid, hchildren[ci], nchildren);
  if (ci < --nchildren)
    {
      pchildren[ci] = pchildren[nchildren];
      hchildren[ci] = hchildren[nchildren];
    }

  return;
}

/* Remove a zombie from zombies by swapping it with the last child in the list.
 */
static void __stdcall
remove_zombie (int ci)
{
  sip_printf ("removing %d, pid %d, nzombies %d", ci, zombies[ci]->pid,
              nzombies);
  if (ci < --nzombies)
    zombies[ci] = zombies[nzombies];

  return;
}

/* Check status of child process vs. waitq member.
 *
 * parent_w is the pointer to the parent of the waitq member in question.
 * child is the subprocess being considered.
 *
 * Returns
 *   1 if stopped or terminated child matches parent_w->next criteria
 *  -1 if a non-stopped/terminated child matches parent_w->next criteria
 *   0 if child does not match parent_w->next criteria
 */
static int __stdcall
stopped_or_terminated (waitq *parent_w, pinfo *child)
{
  int potential_match;
  waitq *w = parent_w->next;

  sip_printf ("considering pid %d", child->pid);
  if (w->pid == -1)
    potential_match = 1;
  else if (w->pid == 0)
    potential_match = child->pgid == myself->pgid;
  else if (w->pid < 0)
    potential_match = child->pgid == -w->pid;
  else
    potential_match = (w->pid == child->pid);

  if (!potential_match)
    return 0;

  BOOL terminated;

  if ((terminated = child->process_state == PID_ZOMBIE) ||
      (w->options & WUNTRACED) && child->stopsig)
    {
      parent_w->next = w->next; /* successful wait.  remove from wait queue */
      w->pid = child->pid;

      if (!terminated)
        {
          sip_printf ("stopped child");
          w->status = (child->stopsig << 8) | 0x7f;
          child->stopsig = 0;
        }
      else
        {
          DWORD status;
          if (!GetExitCodeProcess (child->hProcess, &status))
            status = 0xffff;
          if (status & EXIT_SIGNAL)
            w->status = (status >> 8) & 0xff;   /* exited due to signal */
          else
            w->status = (status & 0xff) << 8;   /* exited via "exit ()" */

          add_rusage (&myself->rusage_children, &child->rusage_children);
          add_rusage (&myself->rusage_children, &child->rusage_self);

          if (w->rusage)
            {
              add_rusage ((struct rusage *) w->rusage, &child->rusage_children);
              add_rusage ((struct rusage *) w->rusage, &child->rusage_self);
            }
          ForceCloseHandle1 (child->hProcess, childhProc);
          child->hProcess = NULL;
          child->process_state = PID_NOT_IN_USE;        /* a reaped child */
        }

      if (!SetEvent (w->ev))    /* wake up wait4 () immediately */
        system_printf ("couldn't wake up wait event %p, %E", w->ev);
      return 1;
    }

  return -potential_match;
}

/* Process signals by waiting for a semaphore to become signaled.
 * Then scan an in-memory array representing queued signals.
 * Executes in a separate thread.
 *
 * Signals sent from this process are sent a completion signal so
 * that returns from kill/raise do not occur until the signal has
 * has been handled, as per POSIX.
 */
static DWORD WINAPI
wait_sig (VOID *)
{
  /* Initialization */
  (void) SetThreadPriority (hwait_sig, WAIT_SIG_PRIORITY);

  /* sigcatch_nosync       - semaphore incremented by sig_dispatch_pending and
   *                         by foreign processes to force an examination of
   *                         the sigtodo array.
   * sigcatch_main         - ditto for local main thread.
   * sigcatch_nonmain      - ditto for local non-main threads.
   *
   * sigcomplete_main      - event used to signal main thread on signal
   *                         completion
   * sigcomplete_nonmain   - semaphore signaled for non-main thread on signal
   *                         completion
   */
  sigcatch_nosync = getsem (NULL, "sigcatch", 0, MAXLONG);
  sigcatch_nonmain = CreateSemaphore (&sec_none_nih, 0, MAXLONG, NULL);
  sigcatch_main = CreateSemaphore (&sec_none_nih, 0, MAXLONG, NULL);
  sigcomplete_nonmain = CreateSemaphore (&sec_none_nih, 0, MAXLONG, NULL);
  sigcomplete_main = CreateEvent (&sec_none_nih, FALSE, FALSE, NULL);
  sigproc_printf ("sigcatch_nonmain %p", sigcatch_nonmain);

  /* Setting dwProcessId flags that this process is now capable of receiving
   * signals.  Prior to this, dwProcessId was set to the windows pid of
   * of the original windows process which spawned us unless this was a
   * "toplevel" process.
   */
  myself->dwProcessId = GetCurrentProcessId ();
  myself->process_state |= PID_ACTIVE;
  myself->process_state &= ~PID_INITIALIZING;

  ProtectHandle (sigcatch_nosync);
  ProtectHandle (sigcatch_nonmain);
  ProtectHandle (sigcatch_main);
  ProtectHandle (sigcomplete_nonmain);
  ProtectHandle (sigcomplete_main);

  /* If we've been execed, then there is still a stub left in the previous
   * windows process waiting to see if it's started a cygwin process or not.
   * Signalling subproc_ready indicates that we are a cygwin process.
   */
  if (child_proc_info && child_proc_info->type == PROC_EXEC)
    {
      debug_printf ("subproc_ready %p", child_proc_info->subproc_ready);
      if (!SetEvent (child_proc_info->subproc_ready))
        system_printf ("SetEvent (subproc_ready) failed, %E");
      ForceCloseHandle (child_proc_info->subproc_ready);
    }

  SetEvent (wait_sig_inited);
  sigtid = GetCurrentThreadId ();

  /* If we got something like a SIGINT while we were initializing, the
     signal thread should be waiting for this event.  This signals the
     thread that it's ok to send the signal since the wait_sig thread
     is now active. */
  extern HANDLE console_handler_thread_waiter;
  SetEvent (console_handler_thread_waiter);

  HANDLE catchem[] = {sigcatch_main, sigcatch_nonmain, sigcatch_nosync};
  sigproc_printf ("Ready.  dwProcessid %d", myself->dwProcessId);
  for (;;)
    {
      DWORD rc = WaitForMultipleObjects (3, catchem, FALSE, sig_loop_wait);

      /* sigproc_terminate sets sig_loop_wait to zero to indicate that
       * this thread should terminate.
       */
      if (rc == WAIT_TIMEOUT)
        if (!sig_loop_wait)
          break;                        // Exiting
        else
          continue;

      if (rc == WAIT_FAILED)
        {
          if (sig_loop_wait != 0)
            system_printf ("WFMO failed, %E");
          break;
        }

      rc -= WAIT_OBJECT_0;
      int dispatched = FALSE;
      sip_printf ("awake");
      /* A sigcatch semaphore has been signaled.  Scan the sigtodo
       * array looking for any unprocessed signals.
       */
      pending_signals = 0;
      int saw_sigchld = 0;
      int dispatched_sigchld = 0;
      for (int sig = -__SIGOFFSET; sig < NSIG; sig++)
        {
          while (InterlockedDecrement (myself->getsigtodo(sig)) >= 0)
            {
              if (sig == SIGCHLD)
                saw_sigchld = 1;
              if (sig > 0 && sig != SIGCONT && sig != SIGKILL && sig != SIGSTOP &&
                  (sigismember (& myself->getsigmask (), sig) ||
                   myself->process_state & PID_STOPPED))
                {
                  sip_printf ("sig %d blocked", sig);
                  break;
                }

              /* Found a signal to process */
              sip_printf ("processing signal %d", sig);
              switch (sig)
                {
                case __SIGFLUSH:
                  /* just forcing the loop */
                  break;

                /* Internal signal to force a flush of strace data to disk. */
                case __SIGSTRACE:
                  // proc_strace ();    // Dump cached strace.prntf stuff.
                  break;

                /* Signalled from a child process that it has stopped */
                case __SIGCHILDSTOPPED:
                  sip_printf ("Received child stopped notification");
                  dispatched |= sig_handle (SIGCHLD, rc);
                  if (proc_subproc (PROC_CHILDSTOPPED, 0))
                    dispatched |= 1;
                  break;

                /* A normal UNIX signal */
                default:
                  sip_printf ("Got signal %d", sig);
                  int wasdispatched = sig_handle (sig, rc);
                  dispatched |= wasdispatched;
                  if (sig == SIGCHLD && wasdispatched)
                    dispatched_sigchld = 1;
                  goto nextsig;
                }
            }
          /* Decremented too far. */
          if (InterlockedIncrement (myself->getsigtodo(sig)) > 0)
            pending_signals = 1;
        nextsig:
          continue;
        }

      if (saw_sigchld && !dispatched_sigchld)
        proc_subproc (PROC_CLEARWAIT, 0);
      /* Signal completion of signal handling depending on which semaphore
       * woke up the WaitForMultipleObjects above.
       */
      switch (rc)
        {
        case 0:
          SetEvent (sigcomplete_main);
sigproc_printf ("signalled sigcomplete_main %p", sigcomplete_main);
          break;
        case 1:
          ReleaseSemaphore (sigcomplete_nonmain, 1, NULL);
sigproc_printf ("signalled sigcomplete_nonmain %p", sigcomplete_nonmain);
          break;
        default:
sigproc_printf ("Did not signal anyone");
          /* Signal from another process.  No need to synchronize. */
          break;
        }

      if (dispatched < 0)
        pending_signals = 1;
      sip_printf ("looping");
    }

  sip_printf ("done");
  return 0;
}

/* Wait for subprocesses to terminate. Executes in a separate thread. */
static DWORD WINAPI
wait_subproc (VOID *)
{
  sip_printf ("starting");
  int errloop = 0;

  for (;;)
    {
      DWORD rc = WaitForMultipleObjects (nchildren + 1, events, FALSE,
                                         proc_loop_wait);
      if (rc == WAIT_TIMEOUT)
        if (!proc_loop_wait)
          break;                        // Exiting
        else
          continue;

      if (rc == WAIT_FAILED)
        {
          if (!proc_loop_wait)
            break;

          /* It's ok to get an ERROR_INVALID_HANDLE since another thread may have
             closed a handle in the children[] array.  So, we try looping a couple
             of times to stabilize. FIXME - this is not foolproof.  Probably, this
             thread should be responsible for closing the children. */
          if (++errloop < 10 && GetLastError () == ERROR_INVALID_HANDLE)
            continue;

          system_printf ("wait failed. nchildren %d, wait %d, %E",
                        nchildren, proc_loop_wait);

          for (int i = 0; i < nchildren + 1; i++)
            if ((rc = WaitForSingleObject (events[i], 0)) == WAIT_OBJECT_0 ||
                rc == WAIT_TIMEOUT)
              continue;
            else
              system_printf ("event[%d] %p, %E", i, events[0]);
          break;
        }

      errloop = 0;
      rc -= WAIT_OBJECT_0;
      if (rc-- != 0)
        (void)proc_subproc (PROC_CHILDTERMINATED, rc);
      sip_printf ("looping");
    }

  ForceCloseHandle (events[0]);
  events[0] = NULL;
  sip_printf ("done");
  return 0;
}