path: root/libjava/posix-threads.cc

// posix-threads.cc - interface between libjava and POSIX threads.

/* Copyright (C) 1998, 1999, 2000, 2001, 2004, 2006  Free Software Foundation

   This file is part of libgcj.

This software is copyrighted work licensed under the terms of the
Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
details.  */

// TO DO:
// * Document signal handling limitations

#include <config.h>

#include "posix.h"
#include "posix-threads.h"

// If we're using the Boehm GC, then we need to override some of the
// thread primitives.  This is fairly gross.
#ifdef HAVE_BOEHM_GC
#include <gc.h>
#endif /* HAVE_BOEHM_GC */

#include <stdlib.h>
#include <time.h>
#include <signal.h>
#include <errno.h>
#include <limits.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>	// To test for _POSIX_THREAD_PRIORITY_SCHEDULING
#endif

#include <gcj/cni.h>
#include <jvm.h>
#include <java/lang/Thread.h>
#include <java/lang/System.h>
#include <java/lang/Long.h>
#include <java/lang/OutOfMemoryError.h>
#include <java/lang/InternalError.h>

// This is used to implement thread startup.
struct starter
{
  _Jv_ThreadStartFunc *method;
  _Jv_Thread_t *data;
};

// This is the key used to map from the POSIX thread value back to the
// Java object representing the thread.  The key is global to all
// threads, so it is ok to make it a global here.
pthread_key_t _Jv_ThreadKey;

// This is the key used to map from the POSIX thread value back to the
// _Jv_Thread_t* representing the thread.
pthread_key_t _Jv_ThreadDataKey;

// We keep a count of all non-daemon threads which are running.  When
// this reaches zero, _Jv_ThreadWait returns.
static pthread_mutex_t daemon_mutex;
static pthread_cond_t daemon_cond;
static int non_daemon_count;

// The signal to use when interrupting a thread.
#if defined(LINUX_THREADS) || defined(FREEBSD_THREADS)
  // LinuxThreads (prior to glibc 2.1) usurps both SIGUSR1 and SIGUSR2.
  // GC on FreeBSD uses both SIGUSR1 and SIGUSR2.
#  define INTR SIGHUP
#else /* LINUX_THREADS */
#  define INTR SIGUSR2
#endif /* LINUX_THREADS */

//
// These are the flags that can appear in _Jv_Thread_t.
//

// Thread started.
#define FLAG_START   0x01
// Thread is daemon.
#define FLAG_DAEMON  0x02



int
_Jv_MutexLock (_Jv_Mutex_t *mu)
{
  pthread_t self = pthread_self ();
  if (mu->owner == self)
    {
      mu->count++;
    }
  else
    {
      JvSetThreadState holder (_Jv_ThreadCurrent(), JV_BLOCKED);
	
#     ifdef LOCK_DEBUG
	int result = pthread_mutex_lock (&mu->mutex);
	if (0 != result)
	  {
	    fprintf(stderr, "Pthread_mutex_lock returned %d\n", result);
	    for (;;) {}
	  }
#     else
        pthread_mutex_lock (&mu->mutex);
#     endif
      mu->count = 1;
      mu->owner = self;
    }
  return 0;
}

// Wait for the condition variable "CV" to be notified. 
// Return values:
// 0: the condition was notified, or the timeout expired.
// _JV_NOT_OWNER: the thread does not own the mutex "MU".   
// _JV_INTERRUPTED: the thread was interrupted. Its interrupted flag is set.   
int
_Jv_CondWait (_Jv_ConditionVariable_t *cv, _Jv_Mutex_t *mu,
	      jlong millis, jint nanos)
{
  pthread_t self = pthread_self();
  if (mu->owner != self)
    return _JV_NOT_OWNER;

  struct timespec ts;

  JvThreadState new_state = JV_WAITING;
  if (millis > 0 || nanos > 0)
    {
      // Calculate the abstime corresponding to the timeout.
      unsigned long long seconds;
      unsigned long usec;

      // For better accuracy, should use pthread_condattr_setclock
      // and clock_gettime.
#ifdef HAVE_GETTIMEOFDAY
      timeval tv;
      gettimeofday (&tv, NULL);
      usec = tv.tv_usec;
      seconds = tv.tv_sec;
#else
      unsigned long long startTime = java::lang::System::currentTimeMillis();
      seconds = startTime / 1000;
      /* Assume we're about half-way through this millisecond.  */
      usec = (startTime % 1000) * 1000 + 500;
#endif
      /* These next two statements cannot overflow.  */
      usec += nanos / 1000;
      usec += (millis % 1000) * 1000;
      /* These two statements could overflow only if tv.tv_sec was
	 insanely large.  */
      seconds += millis / 1000;
      seconds += usec / 1000000;

      ts.tv_sec = seconds;
      if (ts.tv_sec < 0 || (unsigned long long)ts.tv_sec != seconds)
        {
          // We treat a timeout that won't fit into a struct timespec
          // as a wait forever.
          millis = nanos = 0;
        }
      else
	/* This next statement also cannot overflow.  */
	ts.tv_nsec = (usec % 1000000) * 1000 + (nanos % 1000);
    }

  _Jv_Thread_t *current = _Jv_ThreadCurrentData ();
  java::lang::Thread *current_obj = _Jv_ThreadCurrent ();

  pthread_mutex_lock (&current->wait_mutex);

  // Now that we hold the wait mutex, check if this thread has been 
  // interrupted already.
  if (current_obj->interrupt_flag)
    {
      pthread_mutex_unlock (&current->wait_mutex);
      return _JV_INTERRUPTED;
    }

  // Set the thread's state.
  JvSetThreadState holder (current_obj, new_state);

  // Add this thread to the cv's wait set.
  current->next = NULL;

  if (cv->first == NULL)
    cv->first = current;
  else
    for (_Jv_Thread_t *t = cv->first;; t = t->next)
      {
        if (t->next == NULL)
          {
            t->next = current;
            break;
          }
      }

  // Record the current lock depth, so it can be restored when we re-aquire it.
  int count = mu->count;

  // Release the monitor mutex.
  mu->count = 0;
  mu->owner = 0;
  pthread_mutex_unlock (&mu->mutex);
  
  int r = 0;
  bool done_sleeping = false;

  while (! done_sleeping)
    {
      if (millis == 0 && nanos == 0)
	r = pthread_cond_wait (&current->wait_cond, &current->wait_mutex);
      else
	r = pthread_cond_timedwait (&current->wait_cond, &current->wait_mutex, 
				    &ts);

      // In older glibc's (prior to 2.1.3), the cond_wait functions may 
      // spuriously wake up on a signal. Catch that here.
      if (r != EINTR)
        done_sleeping = true;
    }
  
  // Check for an interrupt *before* releasing the wait mutex.
  jboolean interrupted = current_obj->interrupt_flag;
  
  pthread_mutex_unlock (&current->wait_mutex);

  //  Reaquire the monitor mutex, and restore the lock count.
  pthread_mutex_lock (&mu->mutex);
  mu->owner = self;
  mu->count = count;

  // If we were interrupted, or if a timeout occurred, remove ourself from
  // the cv wait list now. (If we were notified normally, notify() will have
  // already taken care of this)
  if (r == ETIMEDOUT || interrupted)
    {
      _Jv_Thread_t *prev = NULL;
      for (_Jv_Thread_t *t = cv->first; t != NULL; t = t->next)
        {
	  if (t == current)
	    {
	      if (prev != NULL)
		prev->next = t->next;
	      else
	        cv->first = t->next;
	      t->next = NULL;
	      break;
	    }
	  prev = t;
	}
      if (interrupted)
	return _JV_INTERRUPTED;
    }
  
  return 0;
}

int
_Jv_CondNotify (_Jv_ConditionVariable_t *cv, _Jv_Mutex_t *mu)
{
  if (_Jv_MutexCheckMonitor (mu))
    return _JV_NOT_OWNER;

  _Jv_Thread_t *target;
  _Jv_Thread_t *prev = NULL;

  for (target = cv->first; target != NULL; target = target->next)
    {
      pthread_mutex_lock (&target->wait_mutex);

      if (target->thread_obj->interrupt_flag)
        {
	  // Don't notify a thread that has already been interrupted.
	  pthread_mutex_unlock (&target->wait_mutex);
          prev = target;
	  continue;
	}

      pthread_cond_signal (&target->wait_cond);
      pthread_mutex_unlock (&target->wait_mutex);

      // Two concurrent notify() calls must not be delivered to the same 
      // thread, so remove the target thread from the cv wait list now.
      if (prev == NULL)
	cv->first = target->next;
      else
        prev->next = target->next;
		
      target->next = NULL;
      
      break;
    }

  return 0;
}

int
_Jv_CondNotifyAll (_Jv_ConditionVariable_t *cv, _Jv_Mutex_t *mu)
{
  if (_Jv_MutexCheckMonitor (mu))
    return _JV_NOT_OWNER;

  _Jv_Thread_t *target;
  _Jv_Thread_t *prev = NULL;

  for (target = cv->first; target != NULL; target = target->next)
    {
      pthread_mutex_lock (&target->wait_mutex);
      pthread_cond_signal (&target->wait_cond);
      pthread_mutex_unlock (&target->wait_mutex);

      if (prev != NULL)
	prev->next = NULL;
      prev = target;
    }
  if (prev != NULL)
    prev->next = NULL;
    
  cv->first = NULL;

  return 0;
}

void
_Jv_ThreadInterrupt (_Jv_Thread_t *data)
{
  pthread_mutex_lock (&data->wait_mutex);

  // Set the thread's interrupted flag *after* aquiring its wait_mutex. This
  // ensures that there are no races with the interrupt flag being set after 
  // the waiting thread checks it and before pthread_cond_wait is entered.
  data->thread_obj->interrupt_flag = true;

  // Interrupt blocking system calls using a signal.
  pthread_kill (data->thread, INTR);
  
  pthread_cond_signal (&data->wait_cond);
  
  pthread_mutex_unlock (&data->wait_mutex);
}

/**
 * Releases the block on a thread created by _Jv_ThreadPark().  This
 * method can also be used to terminate a blockage caused by a prior
 * call to park.  This operation is unsafe, as the thread must be
 * guaranteed to be live.
 *
 * @param thread the thread to unblock.
 */
void
ParkHelper::unpark ()
{
  using namespace ::java::lang;
  volatile obj_addr_t *ptr = &permit;

  /* If this thread is in state RUNNING, give it a permit and return
     immediately.  */
  if (compare_and_swap 
      (ptr, Thread::THREAD_PARK_RUNNING, Thread::THREAD_PARK_PERMIT))
    return;
  
  /* If this thread is parked, put it into state RUNNING and send it a
     signal.  */
  if (compare_and_swap 
      (ptr, Thread::THREAD_PARK_PARKED, Thread::THREAD_PARK_RUNNING))
    {
      pthread_mutex_lock (&mutex);
      pthread_cond_signal (&cond);
      pthread_mutex_unlock (&mutex);
    }
}

/**
 * Sets our state to dead.
 */
void
ParkHelper::deactivate ()
{
  permit = ::java::lang::Thread::THREAD_PARK_DEAD;
}

/**
 * Blocks the thread until a matching _Jv_ThreadUnpark() occurs, the
 * thread is interrupted or the optional timeout expires.  If an
 * unpark call has already occurred, this also counts.  A timeout
 * value of zero is defined as no timeout.  When isAbsolute is true,
 * the timeout is in milliseconds relative to the epoch.  Otherwise,
 * the value is the number of nanoseconds which must occur before
 * timeout.  This call may also return spuriously (i.e.  for no
 * apparent reason).
 *
 * @param isAbsolute true if the timeout is specified in milliseconds from
 *                   the epoch.
 * @param time either the number of nanoseconds to wait, or a time in
 *             milliseconds from the epoch to wait for.
 */
void
ParkHelper::park (jboolean isAbsolute, jlong time)
{
  using namespace ::java::lang;
  volatile obj_addr_t *ptr = &permit;

  /* If we have a permit, return immediately.  */
  if (compare_and_swap 
      (ptr, Thread::THREAD_PARK_PERMIT, Thread::THREAD_PARK_RUNNING))
    return;

  struct timespec ts;
  jlong millis = 0, nanos = 0;

  if (time)
    {
      if (isAbsolute)
	{
	  millis = time;
	  nanos = 0;
	}
      else
	{
	  millis = java::lang::System::currentTimeMillis();
	  nanos = time;
	}

      if (millis > 0 || nanos > 0)
	{
	  // Calculate the abstime corresponding to the timeout.
	  // Everything is in milliseconds.
	  //
	  // We use `unsigned long long' rather than jlong because our
	  // caller may pass up to Long.MAX_VALUE millis.  This would
	  // overflow the range of a timespec.

	  unsigned long long m = (unsigned long long)millis;
	  unsigned long long seconds = m / 1000; 

	  ts.tv_sec = seconds;
	  if (ts.tv_sec < 0 || (unsigned long long)ts.tv_sec != seconds)
	    {
	      // We treat a timeout that won't fit into a struct timespec
	      // as a wait forever.
	      millis = nanos = 0;
	    }
	  else
	    {
	      m %= 1000;
	      ts.tv_nsec = m * 1000000 + (unsigned long long)nanos;
	    }
	}
    }
      
  if (compare_and_swap 
      (ptr, Thread::THREAD_PARK_RUNNING, Thread::THREAD_PARK_PARKED))
    {
      pthread_mutex_lock (&mutex);
      if (millis == 0 && nanos == 0)
	pthread_cond_wait (&cond, &mutex);
      else
	pthread_cond_timedwait (&cond, &mutex, &ts);
      pthread_mutex_unlock (&mutex);
      
      /* If we were unparked by some other thread, this will already
	 be in state THREAD_PARK_RUNNING.  If we timed out, we have to
	 do it ourself.  */
      compare_and_swap 
	(ptr, Thread::THREAD_PARK_PARKED, Thread::THREAD_PARK_RUNNING);
    }
}

static void
handle_intr (int)
{
  // Do nothing.
}

void
_Jv_BlockSigchld()
{
  sigset_t mask;
  sigemptyset (&mask);
  sigaddset (&mask, SIGCHLD);
  int c = pthread_sigmask (SIG_BLOCK, &mask, NULL);
  if (c != 0)
    JvFail (strerror (c));
}

void
_Jv_UnBlockSigchld()
{
  sigset_t mask;
  sigemptyset (&mask);
  sigaddset (&mask, SIGCHLD);
  int c = pthread_sigmask (SIG_UNBLOCK, &mask, NULL);
  if (c != 0)
    JvFail (strerror (c));
}

void
_Jv_InitThreads (void)
{
  pthread_key_create (&_Jv_ThreadKey, NULL);
  pthread_key_create (&_Jv_ThreadDataKey, NULL);
  pthread_mutex_init (&daemon_mutex, NULL);
  pthread_cond_init (&daemon_cond, 0);
  non_daemon_count = 0;

  // Arrange for the interrupt signal to interrupt system calls.
  struct sigaction act;
  act.sa_handler = handle_intr;
  sigemptyset (&act.sa_mask);
  act.sa_flags = 0;
  sigaction (INTR, &act, NULL);

  // Block SIGCHLD here to ensure that any non-Java threads inherit the new 
  // signal mask.
  _Jv_BlockSigchld();

  // Check/set the thread stack size.
  size_t min_ss = 32 * 1024;
  
  if (sizeof (void *) == 8)
    // Bigger default on 64-bit systems.
    min_ss *= 2;

#ifdef PTHREAD_STACK_MIN
  if (min_ss < PTHREAD_STACK_MIN)
    min_ss = PTHREAD_STACK_MIN;
#endif
  
  if (gcj::stack_size > 0 && gcj::stack_size < min_ss)
    gcj::stack_size = min_ss;
}

_Jv_Thread_t *
_Jv_ThreadInitData (java::lang::Thread *obj)
{
  _Jv_Thread_t *data = (_Jv_Thread_t *) _Jv_Malloc (sizeof (_Jv_Thread_t));
  data->flags = 0;
  data->thread_obj = obj;

  pthread_mutex_init (&data->wait_mutex, NULL);
  pthread_cond_init (&data->wait_cond, NULL);

  return data;
}

void
_Jv_ThreadDestroyData (_Jv_Thread_t *data)
{
  pthread_mutex_destroy (&data->wait_mutex);
  pthread_cond_destroy (&data->wait_cond);
  _Jv_Free ((void *)data);
}

void
_Jv_ThreadSetPriority (_Jv_Thread_t *data, jint prio)
{
#ifdef _POSIX_THREAD_PRIORITY_SCHEDULING
  if (data->flags & FLAG_START)
    {
      struct sched_param param;

      param.sched_priority = prio;
      pthread_setschedparam (data->thread, SCHED_OTHER, &param);
    }
#endif
}

void
_Jv_ThreadRegister (_Jv_Thread_t *data)
{
  pthread_setspecific (_Jv_ThreadKey, data->thread_obj);
  pthread_setspecific (_Jv_ThreadDataKey, data);

  // glibc 2.1.3 doesn't set the value of `thread' until after start_routine
  // is called. Since it may need to be accessed from the new thread, work 
  // around the potential race here by explicitly setting it again.
  data->thread = pthread_self ();

# ifdef SLOW_PTHREAD_SELF
    // Clear all self cache slots that might be needed by this thread.
    int dummy;
    int low_index = SC_INDEX(&dummy) + SC_CLEAR_MIN;
    int high_index = SC_INDEX(&dummy) + SC_CLEAR_MAX;
    for (int i = low_index; i <= high_index; ++i) 
      {
        int current_index = i;
	if (current_index < 0)
	  current_index += SELF_CACHE_SIZE;
	if (current_index >= SELF_CACHE_SIZE)
	  current_index -= SELF_CACHE_SIZE;
	_Jv_self_cache[current_index].high_sp_bits = BAD_HIGH_SP_VALUE;
      }
# endif
  // Block SIGCHLD which is used in natPosixProcess.cc.
  _Jv_BlockSigchld();
}

void
_Jv_ThreadUnRegister ()
{
  pthread_setspecific (_Jv_ThreadKey, NULL);
  pthread_setspecific (_Jv_ThreadDataKey, NULL);
}

// This function is called when a thread is started.  We don't arrange
// to call the `run' method directly, because this function must
// return a value.
static void *
really_start (void *x)
{
  struct starter *info = (struct starter *) x;

  _Jv_ThreadRegister (info->data);

  info->method (info->data->thread_obj);

  if (! (info->data->flags & FLAG_DAEMON))
    {
      pthread_mutex_lock (&daemon_mutex);
      --non_daemon_count;
      if (! non_daemon_count)
	pthread_cond_signal (&daemon_cond);
      pthread_mutex_unlock (&daemon_mutex);
    }

  return NULL;
}

void
_Jv_ThreadStart (java::lang::Thread *thread, _Jv_Thread_t *data,
		 _Jv_ThreadStartFunc *meth)
{
  struct sched_param param;
  pthread_attr_t attr;
  struct starter *info;

  if (data->flags & FLAG_START)
    return;
  data->flags |= FLAG_START;

  // Block SIGCHLD which is used in natPosixProcess.cc.
  // The current mask is inherited by the child thread.
  _Jv_BlockSigchld();

  param.sched_priority = thread->getPriority();

  pthread_attr_init (&attr);
  pthread_attr_setschedparam (&attr, &param);
  pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
  
  // Set stack size if -Xss option was given.
  if (gcj::stack_size > 0)
    {
      int e = pthread_attr_setstacksize (&attr, gcj::stack_size);
      if (e != 0)
	JvFail (strerror (e));
    }

  info = (struct starter *) _Jv_AllocBytes (sizeof (struct starter));
  info->method = meth;
  info->data = data;

  if (! thread->isDaemon())
    {
      pthread_mutex_lock (&daemon_mutex);
      ++non_daemon_count;
      pthread_mutex_unlock (&daemon_mutex);
    }
  else
    data->flags |= FLAG_DAEMON;
  int r = pthread_create (&data->thread, &attr, really_start, (void *) info);
  
  pthread_attr_destroy (&attr);

  if (r)
    {
      const char* msg = "Cannot create additional threads";
      throw new java::lang::OutOfMemoryError (JvNewStringUTF (msg));
    }
}

void
_Jv_ThreadWait (void)
{
  pthread_mutex_lock (&daemon_mutex);
  if (non_daemon_count)
    pthread_cond_wait (&daemon_cond, &daemon_mutex);
  pthread_mutex_unlock (&daemon_mutex);
}

#if defined(SLOW_PTHREAD_SELF)

#include "sysdep/locks.h"

// Support for pthread_self() lookup cache.
volatile self_cache_entry _Jv_self_cache[SELF_CACHE_SIZE];

_Jv_ThreadId_t
_Jv_ThreadSelf_out_of_line(volatile self_cache_entry *sce, size_t high_sp_bits)
{
  pthread_t self = pthread_self();
  sce -> high_sp_bits = high_sp_bits;
  write_barrier();
  sce -> self = self;
  return self;
}

#endif /* SLOW_PTHREAD_SELF */