newlib/winsup/cygserver/process.cc

/* process.cc

   Copyright 2001, 2002 Red Hat Inc.

   Written by Robert Collins <rbtcollins@hotmail.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 "woutsup.h"

#include <sys/types.h>

#include <assert.h>
#include <stdlib.h>

#include "cygerrno.h"

#include "process.h"

/*****************************************************************************/

#define elements(ARRAY) (sizeof (ARRAY) / sizeof (*ARRAY))

/*****************************************************************************/

process_cleanup::~process_cleanup ()
{
  delete _process;
}

void
process_cleanup::process ()
{
  _process->cleanup ();
}

/*****************************************************************************/

/* cleanup_routine */
cleanup_routine::~cleanup_routine ()
{
}

/*****************************************************************************/

process::process (const pid_t cygpid, const DWORD winpid)
  : _cygpid (cygpid),
    _winpid (winpid),
    _hProcess (NULL),
    _cleaning_up (false),
    _exit_status (STILL_ACTIVE),
    _routines_head (NULL),
    _next (NULL)
{
  _hProcess = OpenProcess (PROCESS_ALL_ACCESS, FALSE, winpid);
  if (!_hProcess)
    {
      system_printf ("unable to obtain handle for new cache process %d(%lu)",
		     _cygpid, _winpid);
      _hProcess = INVALID_HANDLE_VALUE;
      _exit_status = 0;
    }
  else
    debug_printf ("got handle %p for new cache process %d(%lu)",
		  _hProcess, _cygpid, _winpid);
  InitializeCriticalSection (&_access);
}

process::~process ()
{
  DeleteCriticalSection (&_access);
  (void) CloseHandle (_hProcess);
}

/* No need to be thread-safe as this is only ever called by
 * process_cache::remove_process ().  If it has to be made thread-safe
 * later on, it should not use the `access' critical section as that
 * is held by the client request handlers for an arbitrary length of
 * time, i.e. while they do whatever processing is required for a
 * client request.
 */
DWORD
process::check_exit_code ()
{
  if (_hProcess && _hProcess != INVALID_HANDLE_VALUE
      && _exit_status == STILL_ACTIVE
      && !GetExitCodeProcess (_hProcess, &_exit_status))
    {
      system_printf ("failed to retrieve exit code for %d(%lu), error = %lu",
		     _cygpid, _winpid, GetLastError ());
      _hProcess = INVALID_HANDLE_VALUE;
    }
  return _exit_status;
}

bool
process::add (cleanup_routine *const entry)
{
  assert (entry);

  bool res = false;
  EnterCriticalSection (&_access);

  if (!_cleaning_up)
    {
      entry->_next = _routines_head;
      _routines_head = entry;
      res = true;
    }

  LeaveCriticalSection (&_access);
  return res;
}

bool
process::remove (const cleanup_routine *const entry)
{
  assert (entry);

  bool res = false;
  EnterCriticalSection (&_access);

  if (!_cleaning_up)
    {
      cleanup_routine *previous = NULL;

      for (cleanup_routine *ptr = _routines_head;
	   ptr;
	   previous = ptr, ptr = ptr->_next)
	{
	  if (*ptr == *entry)
	    {
	      if (previous)
		previous->_next = ptr->_next;
	      else
		_routines_head = ptr->_next;

	      delete ptr;
	      res = true;
	      break;
	    }
	}
    }

  LeaveCriticalSection (&_access);
  return res;
}

/* This is single threaded. It's called after the process is removed
 * from the cache, but inserts may be attemped by worker threads that
 * have a pointer to it.
 */
void
process::cleanup ()
{
  EnterCriticalSection (&_access);
  assert (!is_active ());
  assert (!_cleaning_up);
  InterlockedExchange (&_cleaning_up, true);
  cleanup_routine *entry = _routines_head;
  _routines_head = NULL;
  LeaveCriticalSection (&_access);

  while (entry)
    {
      cleanup_routine *const ptr = entry;
      entry = entry->_next;
      ptr->cleanup (this);
      delete ptr;
    }
}

/*****************************************************************************/

void
process_cache::submission_loop::request_loop ()
{
  assert (this);
  assert (_cache);
  assert (_interrupt_event);

  while (_running)
    _cache->wait_for_processes (_interrupt_event);
}

/*****************************************************************************/

process_cache::process_cache (const unsigned int initial_workers)
  : _queue (initial_workers),
    _submitter (this, &_queue),	// true == interruptible
    _processes_count (0),
    _processes_head (NULL),
    _cache_add_trigger (NULL)
{
  /* there can only be one */
  InitializeCriticalSection (&_cache_write_access);

  _cache_add_trigger = CreateEvent (NULL,  // SECURITY_ATTRIBUTES
				    FALSE, // Auto-reset
				    FALSE, // Initially non-signalled
				    NULL); // Anonymous

  if (!_cache_add_trigger)
    {
      system_printf ("failed to create cache add trigger, error = %lu",
		     GetLastError ());
      abort ();
    }

  _queue.add_submission_loop (&_submitter);
}

process_cache::~process_cache ()
{
  (void) CloseHandle (_cache_add_trigger);
  DeleteCriticalSection (&_cache_write_access);
}

/* This returns the process object to the caller already locked, that
 * is, with the object's `access' critical region entered.  Thus the
 * caller must unlock the object when it's finished with it (via
 * process::release ()).  It must then not try to access the object
 * afterwards, except by going through this routine again, as it may
 * have been deleted once it has been unlocked.
 */
class process *
process_cache::process (const pid_t cygpid, const DWORD winpid)
{
  /* TODO: make this more granular, so a search doesn't involve the
   * write lock.
   */
  EnterCriticalSection (&_cache_write_access);
  class process *previous = NULL;
  class process *entry = find (winpid, &previous);

  if (!entry)
    {
      if (_processes_count + SPECIALS_COUNT >= MAXIMUM_WAIT_OBJECTS)
	{
	  LeaveCriticalSection (&_cache_write_access);
	  system_printf (("process limit (%d processes) reached; "
			  "new connection refused for %d(%lu)"),
			 MAXIMUM_WAIT_OBJECTS - SPECIALS_COUNT,
			 cygpid, winpid);
	  set_errno (EAGAIN);
	  return NULL;
	}

      entry = new class process (cygpid, winpid);
      if (!entry->is_active ())
	{
	  LeaveCriticalSection (&_cache_write_access);
	  delete entry;
	  set_errno (ESRCH);
	  return NULL;
	}

      if (previous)
	{
	  entry->_next = previous->_next;
	  previous->_next = entry;
	}
      else
	{
	  entry->_next = _processes_head;
	  _processes_head = entry;
	}

      _processes_count += 1;
      SetEvent (_cache_add_trigger);
    }

  EnterCriticalSection (&entry->_access); // To be released by the caller.
  LeaveCriticalSection (&_cache_write_access);
  assert (entry);
  assert (entry->_winpid == winpid);
  return entry;
}

void
process_cache::wait_for_processes (const HANDLE interrupt_event)
{
  // Update `_wait_array' with handles of all current processes.
  const size_t count = sync_wait_array (interrupt_event);

  debug_printf ("waiting on %u objects in total (%u processes)",
		count, _processes_count);

  const DWORD rc = WaitForMultipleObjects (count, _wait_array,
					   FALSE, INFINITE);

  if (rc == WAIT_FAILED)
    {
      system_printf ("could not wait on the process handles, error = %lu",
		     GetLastError ());
      abort ();
    }

  const size_t start = rc - WAIT_OBJECT_0;

  if (rc < WAIT_OBJECT_0 || start > count)
    {
      system_printf (("unexpected return code %rc "
		      "from WaitForMultipleObjects: "
		      "expected [%u .. %u)"),
		     rc, WAIT_OBJECT_0, WAIT_OBJECT_0 + count);
      abort ();
    }

  // Tell all the processes, from the signalled point up, the bad news.
  for (size_t index = start; index != count; index++)
    if (_process_array[index])
      check_and_remove_process (index);
}

/*
 * process_cache::sync_wait_array ()
 *
 * Fill-in the wait array with the handles that the cache needs to wait on.
 * These handles are:
 *  - the process_process_param's interrupt event
 *  - the process_cache's cache_add_trigger event
 *  - the handle for each live process in the cache.
 *
 * Return value: the number of live handles in the array.
 */

size_t
process_cache::sync_wait_array (const HANDLE interrupt_event)
{
  assert (this);
  assert (_cache_add_trigger && _cache_add_trigger != INVALID_HANDLE_VALUE);
  assert (interrupt_event && interrupt_event != INVALID_HANDLE_VALUE);

  EnterCriticalSection (&_cache_write_access);

  assert (_processes_count + SPECIALS_COUNT <= elements (_wait_array));

  size_t index = 0;

  for (class process *ptr = _processes_head; ptr; ptr = ptr->_next)
    {
      assert (ptr->_hProcess && ptr->_hProcess != INVALID_HANDLE_VALUE);
      assert (ptr->is_active ());

      _wait_array[index] = ptr->handle ();
      _process_array[index++] = ptr;

      assert (index <= elements (_wait_array));
    }

  /* Sorry for shouting, but THESE MUST BE ADDED AT THE END! */
  /* Well, not strictly `must', but it's more efficient if they are :-) */

  _wait_array[index] = interrupt_event;
  _process_array[index++] = NULL;

  _wait_array[index] = _cache_add_trigger;
  _process_array[index++] = NULL;

  /* Phew, back to normal volume now. */

  assert (index <= elements (_wait_array));

  LeaveCriticalSection (&_cache_write_access);

  return index;
}

void
process_cache::check_and_remove_process (const size_t index)
{
  assert (this);
  assert (index < elements (_wait_array) - SPECIALS_COUNT);

  class process *const process = _process_array[index];

  assert (process);
  assert (process->handle () == _wait_array[index]);

  if (process->check_exit_code () == STILL_ACTIVE)
    return;

  debug_printf ("process %d(%lu) has left the building ($? = %lu)",
		process->_cygpid, process->_winpid, process->_exit_status);

  /* Unlink the process object from the process list. */

  EnterCriticalSection (&_cache_write_access);

  class process *previous = NULL;

  const class process *const tmp = find (process->_winpid, &previous);

  assert (tmp == process);
  assert (previous ? previous->_next == process : _processes_head == process);

  if (previous)
    previous->_next = process->_next;
  else
    _processes_head = process->_next;

  _processes_count -= 1;
  LeaveCriticalSection (&_cache_write_access);

  /* Schedule any cleanup tasks for this process. */
  _queue.add (new process_cleanup (process));
}

class process *
process_cache::find (const DWORD winpid, class process **previous)
{
  if (previous)
    *previous = NULL;

  for (class process *ptr = _processes_head; ptr; ptr = ptr->_next)
    if (ptr->_winpid == winpid)
      return ptr;
    else if (ptr->_winpid > winpid) // The list is sorted by winpid.
      return NULL;
    else if (previous)
      *previous = ptr;

  return NULL;
}

/*****************************************************************************/