path: root/ace/SV_Semaphore_Complex.cpp

// SV_Semaphore_Complex.cpp
// $Id$

/* -*- C++ -*- */

#define ACE_BUILD_DLL
#include "ace/SV_Semaphore_Complex.h"

ACE_ALLOC_HOOK_DEFINE(ACE_SV_Semaphore_Complex)

void
ACE_SV_Semaphore_Complex::dump (void) const
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::dump");
}

// initial value of process 
const int ACE_SV_Semaphore_Complex::BIGCOUNT_ = 10000;

// Define the ACE_SV_Semaphore operation arrays for the semop() calls. 
sembuf ACE_SV_Semaphore_Complex::op_lock_[2] = 
{
  {0, 0, 0},			// Wait for [0] (lock) to equal 0 
  {0, 1, SEM_UNDO},		// then increment [0] to 1 - this locks it. 
                                // UNDO to release the lock if processes exit 
				// before explicitly unlocking. 
};

sembuf ACE_SV_Semaphore_Complex::op_endcreate_[2] = 
{
  {1, -1, SEM_UNDO},		// Decrement [1] (proc counter) with undo on 
                                // exit, UNDO to adjust proc counter if 
				// process exits before explicitly calling close() 
  {0, -1, SEM_UNDO},		// the decrement [0] (lock) back to 0 
};

sembuf ACE_SV_Semaphore_Complex::op_open_[1] = 
{
  {1, -1, SEM_UNDO},		// Decrement [1] (proc counter) with undo on 
                                // exit. 
};

sembuf ACE_SV_Semaphore_Complex::op_close_[3] = 
{
  {0, 0, 0},			// Wait for [0] (lock) to equal 0 
  {0, 1, SEM_UNDO},		// then increment [0] to 1 - this lock it 
  {1, 1, SEM_UNDO},		// then increment [1] (proc counter) 
};

sembuf ACE_SV_Semaphore_Complex::op_unlock_[1] = 
{
  {0, -1, SEM_UNDO},		// Decrement [0] (lock) back to 0 
};

// Open or create an array of SV_Semaphores.  We return 0 if all is OK, else -1. 

int 
ACE_SV_Semaphore_Complex::open (key_t k, 
				int create, 
				int initial_value, 
				u_short nsems, 
				int perms)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::open");
  if (k == IPC_PRIVATE)
    return -1;

  this->key_ = k;
  
  if (create == ACE_SV_Semaphore_Complex::ACE_CREATE)
    {
      int result;

      do
	{
	  this->internal_id_ = ACE_OS::semget 
	    (this->key_, (u_short) 2 + nsems, perms | ACE_SV_Semaphore_Complex::ACE_CREATE);

	  if (this->internal_id_ == -1)
	    return -1; // permission problem or tables full 
      
	  // When the ACE_SV_Semaphore is created, we know that the
	  // value of all 3 members is 0. Get a lock on the
	  // ACE_SV_Semaphore by waiting for [0] to equal 0, then
	  // increment it.
	     
	  // There is a race condition here. There is the possibility
	  // that between the semget() above and the semop() below,
	  // another process can call out close() function which can
	  // remove the ACE_SV_Semaphore if that process is the last
	  // one using it.  Therefor we handle the error condition of
	  // an invalid ACE_SV_Semaphore ID specifically below, and if
	  // it does happen, we just go back and create it again.
	  result = ACE_OS::semop (this->internal_id_, 
				  &ACE_SV_Semaphore_Complex::op_lock_[0], 
				  2);
	}
      while (result == -1 && (errno == EINVAL || errno == EIDRM));

      if (result == -1)
	return -1;

      // Get the value of the process counter. If it equals 0, then no
      // one has initialized the ACE_SV_Semaphore yet.
        
      int semval = ACE_SV_Semaphore_Simple::control (GETVAL, 0, 1);
  
      if (semval == -1)
	return this->init ();
      else if (semval == 0)
	{
	  // We should initialize by doing a SETALL, but that would
	  // clear the adjust value that we set when we locked the
	  // ACE_SV_Semaphore above. Instead we do system calls to
	  // initialize [1], as well as all the nsems SV_Semaphores.
	        
	  if (ACE_SV_Semaphore_Simple::control (SETVAL, 
						ACE_SV_Semaphore_Complex::BIGCOUNT_, 
						1) == -1)
	    return -1;
	  else
	    for (int i = 0; i < nsems; i++)
	      if (this->control (SETVAL, initial_value, i) == -1)
		return -1;
	}	      
  
      // Decrement the process counter and then release the lock. 
      return ACE_OS::semop (this->internal_id_, 
			    &ACE_SV_Semaphore_Complex::op_endcreate_[0], 
			    2);
    }
  else 
    {
      this->internal_id_ = ACE_OS::semget (this->key_, 2 + nsems, 0);
      if (this->internal_id_ == -1)
	return -1;			// doesn't exist or tables full 
  
      // Decrement the process counter. We don't need a lock to do this. 
      if (ACE_OS::semop (this->internal_id_, 
			 &ACE_SV_Semaphore_Complex::op_open_[0], 1) < 0)
	return this->init ();
      return 0;
    }
}

int 
ACE_SV_Semaphore_Complex::open (const char *name, 
				int flags, 
				int initial_value, 
				u_short nsems, 
				int perms)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::open");
  return this->open (ACE_SV_Semaphore_Simple::name_2_key (name), 
		     flags, initial_value, nsems, perms);
}

// Close a ACE_SV_Semaphore.  Unlike the remove above, this function
// is for a process to call before it exits, when it is done with the
// ACE_SV_Semaphore.  We "decrement" the counter of processes using
// the ACE_SV_Semaphore, and if this was the last one, we can remove
// the ACE_SV_Semaphore.

int 
ACE_SV_Semaphore_Complex::close (void)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::close");
  int semval;
  
  if (this->key_ <= (key_t) - 1 || this->internal_id_ == -1)
    return -1;
  
  // The following semop() first gets a lock on the ACE_SV_Semaphore,
  // then increments [1] - the process number.
  
  if (ACE_OS::semop (this->internal_id_, 
		     &ACE_SV_Semaphore_Complex::op_close_[0], 
		     3) == -1)
    return -1;
  
  // Now that we have a lock, read the value of the process counter to
  // see if this is the last reference to the ACE_SV_Semaphore. There
  // is a race condition here - see the comments in create ().
  
  if ((semval = ACE_SV_Semaphore_Simple::control (GETVAL, 0, 1)) == -1)
    return -1;
  
  if (semval > ACE_SV_Semaphore_Complex::BIGCOUNT_)
    return -1;
  else if (semval == ACE_SV_Semaphore_Complex::BIGCOUNT_)
    return this->remove ();
  else
    {
      int result = ACE_OS::semop (this->internal_id_, 
				  &ACE_SV_Semaphore_Complex::op_unlock_[0], 1);
      this->init ();
      return result;
    }
}

ACE_SV_Semaphore_Complex::ACE_SV_Semaphore_Complex (key_t k, 
						    int flags, 
						    int initial_value, 
						    u_short nsems, 
						    int perms)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::ACE_SV_Semaphore_Complex");
  if (this->open (k, flags, initial_value, nsems, perms) == -1)
    ACE_ERROR ((LM_ERROR, "%p\n", "ACE_SV_Semaphore_Complex"));
}

ACE_SV_Semaphore_Complex::ACE_SV_Semaphore_Complex (const char *name, 
						    int flags, 
						    int initial_value, 
						    u_short nsems, 
						    int perms)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::ACE_SV_Semaphore_Complex");

  key_t key;
  
  if (name == 0)
    key = ACE_DEFAULT_SEM_KEY;
  else 
    key = this->name_2_key (name);

  if (this->open (key, flags, initial_value, nsems, perms) == -1)
    ACE_ERROR ((LM_ERROR, "%p\n", "ACE_SV_Semaphore_Complex"));
}

ACE_SV_Semaphore_Complex::~ACE_SV_Semaphore_Complex (void)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::~ACE_SV_Semaphore_Complex");
  if (this->internal_id_ >= 0)
    this->close ();
}

ACE_SV_Semaphore_Complex::ACE_SV_Semaphore_Complex (void)
{
  ACE_TRACE ("ACE_SV_Semaphore_Complex::ACE_SV_Semaphore_Complex");
  this->init ();
}