emacs/src/systhread.c

/* System thread definitions
Copyright (C) 2012-2024 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>
#include <setjmp.h>
#include <stdio.h>
#include <string.h>
#include "lisp.h"

#ifdef HAVE_NS
#include "nsterm.h"
#endif

#ifdef HAVE_PTHREAD_SET_NAME_NP
#include <pthread_np.h>
#endif

#ifndef THREADS_ENABLED

void
sys_mutex_init (sys_mutex_t *m)
{
  *m = 0;
}

void
sys_mutex_lock (sys_mutex_t *m)
{
}

void
sys_mutex_unlock (sys_mutex_t *m)
{
}

void
sys_cond_init (sys_cond_t *c)
{
  *c = 0;
}

void
sys_cond_wait (sys_cond_t *c, sys_mutex_t *m)
{
}

void
sys_cond_signal (sys_cond_t *c)
{
}

void
sys_cond_broadcast (sys_cond_t *c)
{
}

void
sys_cond_destroy (sys_cond_t *c)
{
}

sys_thread_t
sys_thread_self (void)
{
  return 0;
}

bool
sys_thread_equal (sys_thread_t t, sys_thread_t u)
{
  return t == u;
}
void
sys_thread_set_name (const char *name)
{
}

bool
sys_thread_create (sys_thread_t *t, thread_creation_function *func, void *datum)
{
  return false;
}

void
sys_thread_yield (void)
{
}

#elif defined (HAVE_PTHREAD)

#include <sched.h>

void
sys_mutex_init (sys_mutex_t *mutex)
{
  pthread_mutexattr_t *attr_ptr;
#ifdef ENABLE_CHECKING
  pthread_mutexattr_t attr;
  {
    int error = pthread_mutexattr_init (&attr);
    eassert (error == 0);
    error = pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ERRORCHECK);
    eassert (error == 0);
  }
  attr_ptr = &attr;
#else
  attr_ptr = NULL;
#endif
  int error = pthread_mutex_init (mutex, attr_ptr);
  /* We could get ENOMEM.  Can't do anything except aborting.  */
  if (error != 0)
    {
      fprintf (stderr, "\npthread_mutex_init failed: %s\n", strerror (error));
      emacs_abort ();
    }
#ifdef ENABLE_CHECKING
  error = pthread_mutexattr_destroy (&attr);
  eassert (error == 0);
#endif
}

void
sys_mutex_lock (sys_mutex_t *mutex)
{
  int error = pthread_mutex_lock (mutex);
  eassert (error == 0);
}

void
sys_mutex_unlock (sys_mutex_t *mutex)
{
  int error = pthread_mutex_unlock (mutex);
  eassert (error == 0);
}

void
sys_cond_init (sys_cond_t *cond)
{
  int error = pthread_cond_init (cond, NULL);
  /* We could get ENOMEM.  Can't do anything except aborting.  */
  if (error != 0)
    {
      fprintf (stderr, "\npthread_cond_init failed: %s\n", strerror (error));
      emacs_abort ();
    }
}

void
sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
{
  int error = pthread_cond_wait (cond, mutex);
  eassert (error == 0);
}

void
sys_cond_signal (sys_cond_t *cond)
{
  int error = pthread_cond_signal (cond);
  eassert (error == 0);
}

void
sys_cond_broadcast (sys_cond_t *cond)
{
  int error = pthread_cond_broadcast (cond);
  eassert (error == 0);
#ifdef HAVE_NS
  /* Send an app defined event to break out of the NS run loop.
     It seems that if ns_select is running the NS run loop, this
     broadcast has no effect until the loop is done, breaking a couple
     of tests in thread-tests.el. */
  ns_run_loop_break ();
#endif
}

void
sys_cond_destroy (sys_cond_t *cond)
{
  int error = pthread_cond_destroy (cond);
  eassert (error == 0);
}

sys_thread_t
sys_thread_self (void)
{
  return pthread_self ();
}

bool
sys_thread_equal (sys_thread_t t, sys_thread_t u)
{
  return pthread_equal (t, u);
}

void
sys_thread_set_name (const char *name)
{
#ifdef HAVE_PTHREAD_SETNAME_NP
  /* We need to truncate here otherwise pthread_setname_np
     fails to set the name.  TASK_COMM_LEN is what the length
     is called in the Linux kernel headers (Bug#38632).  */
#define TASK_COMM_LEN 16
  char p_name[TASK_COMM_LEN];
  strncpy (p_name, name, TASK_COMM_LEN - 1);
  p_name[TASK_COMM_LEN - 1] = '\0';
# ifdef HAVE_PTHREAD_SETNAME_NP_1ARG
  pthread_setname_np (p_name);
# elif defined HAVE_PTHREAD_SETNAME_NP_3ARG
  pthread_setname_np (pthread_self (), "%s", p_name);
# else
  pthread_setname_np (pthread_self (), p_name);
# endif
#elif HAVE_PTHREAD_SET_NAME_NP
  /* The name will automatically be truncated if it exceeds a
     system-specific length.  */
  pthread_set_name_np (pthread_self (), name);
#endif
}

bool
sys_thread_create (sys_thread_t *thread_ptr, thread_creation_function *func,
                   void *arg)
{
  pthread_attr_t attr;
  bool result = false;

  if (pthread_attr_init (&attr))
    return false;

  /* Avoid crash on macOS with deeply nested GC (Bug#30364).  */
  size_t stack_size;
  size_t required_stack_size = sizeof (void *) * 1024 * 1024;
  if (pthread_attr_getstacksize (&attr, &stack_size) == 0
      && stack_size < required_stack_size)
    {
      if (pthread_attr_setstacksize (&attr, required_stack_size) != 0)
        goto out;
    }

  if (!pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED))
    result = pthread_create (thread_ptr, &attr, func, arg) == 0;

 out: ;
  int error = pthread_attr_destroy (&attr);
  eassert (error == 0);

  return result;
}

void
sys_thread_yield (void)
{
  sched_yield ();
}

#elif defined (WINDOWSNT)

#include <mbctype.h>
#include "w32term.h"

/* Cannot include <process.h> because of the local header by the same
   name, sigh.  */
uintptr_t _beginthread (void (__cdecl *)(void *), unsigned, void *);

/* Mutexes are implemented as critical sections, because they are
   faster than Windows mutex objects (implemented in userspace), and
   satisfy the requirements, since we only need to synchronize within a
   single process.  */
void
sys_mutex_init (sys_mutex_t *mutex)
{
  InitializeCriticalSection ((LPCRITICAL_SECTION)mutex);
}

void
sys_mutex_lock (sys_mutex_t *mutex)
{
  /* FIXME: What happens if the owning thread exits without releasing
     the mutex?  According to MSDN, the result is undefined behavior.  */
  EnterCriticalSection ((LPCRITICAL_SECTION)mutex);
}

void
sys_mutex_unlock (sys_mutex_t *mutex)
{
  LeaveCriticalSection ((LPCRITICAL_SECTION)mutex);
}

void
sys_cond_init (sys_cond_t *cond)
{
  cond->initialized = false;
  cond->wait_count = 0;
  /* Auto-reset event for signal.  */
  cond->events[CONDV_SIGNAL] = CreateEvent (NULL, FALSE, FALSE, NULL);
  /* Manual-reset event for broadcast.  */
  cond->events[CONDV_BROADCAST] = CreateEvent (NULL, TRUE, FALSE, NULL);
  if (!cond->events[CONDV_SIGNAL] || !cond->events[CONDV_BROADCAST])
    return;
  InitializeCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
  cond->initialized = true;
}

void
sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
{
  DWORD wait_result;
  bool last_thread_waiting;

  if (!cond->initialized)
    return;

  /* Increment the wait count avoiding race conditions.  */
  EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
  cond->wait_count++;
  LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);

  /* Release the mutex and wait for either the signal or the broadcast
     event.  */
  LeaveCriticalSection ((LPCRITICAL_SECTION)mutex);
  wait_result = WaitForMultipleObjects (2, cond->events, FALSE, INFINITE);

  /* Decrement the wait count and see if we are the last thread
     waiting on the condition variable.  */
  EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
  cond->wait_count--;
  last_thread_waiting =
    wait_result == WAIT_OBJECT_0 + CONDV_BROADCAST
    && cond->wait_count == 0;
  LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);

  /* Broadcast uses a manual-reset event, so when the last thread is
     released, we must manually reset that event.  */
  if (last_thread_waiting)
    ResetEvent (cond->events[CONDV_BROADCAST]);

  /* Per the API, re-acquire the mutex.  */
  EnterCriticalSection ((LPCRITICAL_SECTION)mutex);
}

void
sys_cond_signal (sys_cond_t *cond)
{
  bool threads_waiting;

  if (!cond->initialized)
    return;

  EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
  threads_waiting = cond->wait_count > 0;
  LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);

  if (threads_waiting)
    SetEvent (cond->events[CONDV_SIGNAL]);
}

void
sys_cond_broadcast (sys_cond_t *cond)
{
  bool threads_waiting;

  if (!cond->initialized)
    return;

  EnterCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
  threads_waiting = cond->wait_count > 0;
  LeaveCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);

  if (threads_waiting)
    SetEvent (cond->events[CONDV_BROADCAST]);
}

void
sys_cond_destroy (sys_cond_t *cond)
{
  if (cond->events[CONDV_SIGNAL])
    CloseHandle (cond->events[CONDV_SIGNAL]);
  if (cond->events[CONDV_BROADCAST])
    CloseHandle (cond->events[CONDV_BROADCAST]);

  if (!cond->initialized)
    return;

  /* FIXME: What if wait_count is non-zero, i.e. there are still
     threads waiting on this condition variable?  */
  DeleteCriticalSection ((LPCRITICAL_SECTION)&cond->wait_count_lock);
}

sys_thread_t
sys_thread_self (void)
{
  return (sys_thread_t) GetCurrentThreadId ();
}

bool
sys_thread_equal (sys_thread_t t, sys_thread_t u)
{
  return t == u;
}

/* Special exception used to communicate with a debugger.  The name is
   taken from example code shown on MSDN.  */
#define MS_VC_EXCEPTION 0x406d1388UL

/* Structure used to communicate thread name to a debugger.  */
typedef struct _THREADNAME_INFO
{
  DWORD_PTR  type;
  LPCSTR name;
  DWORD_PTR  thread_id;
  DWORD_PTR  reserved;
} THREADNAME_INFO;

typedef BOOL (WINAPI *IsDebuggerPresent_Proc) (void);
extern IsDebuggerPresent_Proc is_debugger_present;
extern int (WINAPI *pMultiByteToWideChar)(UINT,DWORD,LPCSTR,int,LPWSTR,int);
typedef HRESULT (WINAPI *SetThreadDescription_Proc)
  (HANDLE hThread, PCWSTR lpThreadDescription);
extern SetThreadDescription_Proc set_thread_description;

/* Set the name of the thread identified by its thread ID.  */
static void
w32_set_thread_name (DWORD thread_id, const char *name)
{
  if (!name || !*name)
    return;

  /* Use the new API provided since Windows 10, if available.  */
  if (set_thread_description)
    {
      /* GDB pulls only the first 1024 characters of thread's name.  */
      wchar_t name_w[1025];
      /* The thread name is encoded in locale's encoding, but
	 SetThreadDescription wants a wchar_t string.  */
      int codepage = _getmbcp ();
      if (!codepage)
	codepage = GetACP ();
      int cnv_result = pMultiByteToWideChar (codepage, MB_ERR_INVALID_CHARS,
					     name, -1,
					     name_w, 1025);
      if (cnv_result
	  && set_thread_description (GetCurrentThread (), name_w) == S_OK)
	return;
    }
  /* We can only support this fallback method when Emacs is being
     debugged.  */
  if (!(is_debugger_present && is_debugger_present ()))
    return;

  THREADNAME_INFO tninfo;

  tninfo.type = 0x1000;	/* magic constant */
  tninfo.name = name;
  tninfo.thread_id = thread_id;
  tninfo.reserved = 0;
  RaiseException (MS_VC_EXCEPTION, 0, sizeof (tninfo) / sizeof (ULONG_PTR),
		  (ULONG_PTR *) &tninfo);
}

static thread_creation_function *thread_start_address;

void
sys_thread_set_name (const char *name)
{
  w32_set_thread_name (GetCurrentThreadId (), name);
}

/* _beginthread wants a void function, while we are passed a function
   that returns a pointer.  So we use a wrapper.  See the command in
   w32term.h about the need for ALIGN_STACK attribute.  */
static void ALIGN_STACK
w32_beginthread_wrapper (void *arg)
{
  (void)thread_start_address (arg);
}

bool
sys_thread_create (sys_thread_t *thread_ptr, thread_creation_function *func,
                   void *arg)
{
  /* FIXME: Do threads that run Lisp require some minimum amount of
     stack?  Zero here means each thread will get the same amount as
     the main program.  On GNU/Linux, it seems like the stack is 2MB
     by default, overridden by RLIMIT_STACK at program start time.
     Not sure what to do with this.  See also the comment in
     w32proc.c:new_child.  */
  const unsigned stack_size = 0;
  uintptr_t thandle;

  thread_start_address = func;

  /* We use _beginthread rather than CreateThread because the former
     arranges for the thread handle to be automatically closed when
     the thread exits, thus preventing handle leaks and/or the need to
     track all the threads and close their handles when they exit.
     Also, MSDN seems to imply that code which uses CRT _must_ call
     _beginthread, although if that is true, we already violate that
     rule in many places...  */
  thandle = _beginthread (w32_beginthread_wrapper, stack_size, arg);
  if (thandle == (uintptr_t)-1L)
    return false;

  /* Kludge alert!  We use the Windows thread ID, an unsigned 32-bit
     number, as the sys_thread_t type, because that ID is the only
     unique identifier of a thread on Windows.  But _beginthread
     returns a handle of the thread, and there's no easy way of
     getting the thread ID given a handle (GetThreadId is available
     only since Vista, so we cannot use it portably).  Fortunately,
     the value returned by sys_thread_create is not used by its
     callers; instead, run_thread, which runs in the context of the
     new thread, calls sys_thread_self and uses its return value;
     sys_thread_self in this implementation calls GetCurrentThreadId.
     Therefore, we return some more or less arbitrary value of the
     thread ID from this function. */
  *thread_ptr = thandle & 0xFFFFFFFF;
  return true;
}

void
sys_thread_yield (void)
{
  Sleep (0);
}

#else

#error port me

#endif