readwritesem.cpp

Pegasus is an open-source implementationof the DMTF CIM and WBEM standards. It is designed to be por

//%2006////////////////////////////////////////////////////////////////////////
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// Copyright (c) 2000, 2001, 2002 BMC Software; Hewlett-Packard Development
// Company, L.P.; IBM Corp.; The Open Group; Tivoli Systems.
// Copyright (c) 2003 BMC Software; Hewlett-Packard Development Company, L.P.;
// IBM Corp.; EMC Corporation, The Open Group.
// Copyright (c) 2004 BMC Software; Hewlett-Packard Development Company, L.P.;
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// Copyright (c) 2005 Hewlett-Packard Development Company, L.P.; IBM Corp.;
// EMC Corporation; VERITAS Software Corporation; The Open Group.
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#include "ReadWriteSem.h"
#include "Time.h"
#include "PegasusAssert.h"
#include "Threads.h"

PEGASUS_NAMESPACE_BEGIN

//==============================================================================
//
// PEGASUS_USE_POSIX_RWLOCK
//
//==============================================================================

#ifdef PEGASUS_USE_POSIX_RWLOCK

ReadWriteSem::ReadWriteSem():_readers(0), _writers(0)
{
    pthread_rwlock_init(&_rwlock.rwlock, NULL);
    Threads::clear(_rwlock.owner);
}

ReadWriteSem::~ReadWriteSem()
{
    int r = 0;
    while (r=pthread_rwlock_destroy(&_rwlock.rwlock) == EBUSY ||
           (r == -1 && errno == EBUSY))
    {
        Threads::yield();
    }
}

void ReadWriteSem::wait(Uint32 mode, ThreadType caller)
{
    int errorcode;
    if (mode == PEG_SEM_READ)
    {
        if (0 == (errorcode = pthread_rwlock_rdlock(&_rwlock.rwlock)))
        {
            _readers++;
            return;
        }
    }
    else if (mode == PEG_SEM_WRITE)
    {
        if (0 == (errorcode = pthread_rwlock_wrlock(&_rwlock.rwlock)))
        {
            _rwlock.owner = caller;
            _writers++;
            return;
        }
    }
    else
        throw(Permission(Threads::self()));

    if (errorcode == EDEADLK)
        throw(Deadlock(_rwlock.owner));
    else
        throw(WaitFailed(Threads::self()));
}

void ReadWriteSem::try_wait(Uint32 mode, ThreadType caller)
{
    int errorcode = 0;
    if (mode == PEG_SEM_READ)
    {
        if (0 == (errorcode = pthread_rwlock_tryrdlock(&_rwlock.rwlock)))
        {
            _readers++;
            return;
        }
    }
    else if (mode == PEG_SEM_WRITE)
    {
        if (0 == (errorcode = pthread_rwlock_trywrlock(&_rwlock.rwlock)))
        {
            _writers++;
            _rwlock.owner = caller;
            return;
        }
    }
    else
        throw(Permission(Threads::self()));
    if (errorcode == -1)
        errorcode = errno;
    if (errorcode == EBUSY)
        throw(AlreadyLocked(_rwlock.owner));
    else if (errorcode == EDEADLK)
        throw(Deadlock(_rwlock.owner));
    else
        throw(WaitFailed(Threads::self()));
}


// timedrdlock and timedwrlock are not supported on HPUX
// mdday Sun Aug  5 14:21:00 2001
void ReadWriteSem::timed_wait(Uint32 mode,
                              ThreadType caller, int milliseconds)
{
    int errorcode = 0, timeout = 0;
    struct timeval now, finish, remaining;
    Uint32 usec;

    gettimeofday(&finish, NULL);
    finish.tv_sec += (milliseconds / 1000);
    milliseconds %= 1000;
    usec = finish.tv_usec + (milliseconds * 1000);
    finish.tv_sec += (usec / 1000000);
    finish.tv_usec = usec % 1000000;

    if (mode == PEG_SEM_READ)
    {
        do
        {
            errorcode = pthread_rwlock_tryrdlock(&_rwlock.rwlock);
            if (errorcode == -1)
                errorcode = errno;
            gettimeofday(&now, NULL);
        }
        while (errorcode == EBUSY &&
               (0 == (timeout = Time::subtract(&remaining, &finish, &now))));
        if (0 == errorcode)
        {
            _readers++;
            return;
        }
    }
    else if (mode == PEG_SEM_WRITE)
    {
        do
        {
            errorcode = pthread_rwlock_trywrlock(&_rwlock.rwlock);
            if (errorcode == -1)
                errorcode = errno;
            gettimeofday(&now, NULL);
        }
        while (errorcode == EBUSY &&
               (0 == (timeout = Time::subtract(&remaining, &finish, &now))));

        if (0 == errorcode)
        {
            _writers++;
            _rwlock.owner = caller;
            return;
        }
    }
    else
        throw(Permission(Threads::self()));
    if (timeout != 0)
        throw(TimeOut(_rwlock.owner));
    else if (errorcode == EDEADLK)
        throw(Deadlock(_rwlock.owner));
    else
        throw(WaitFailed(Threads::self()));
}

void ReadWriteSem::unlock(Uint32 mode, ThreadType caller)
{
    ThreadType owner;

    if (mode == PEG_SEM_WRITE)
    {
        owner = _rwlock.owner;
        Threads::clear(_rwlock.owner);
    }
    if (0 != pthread_rwlock_unlock(&_rwlock.rwlock))
    {
        _rwlock.owner = owner;
        throw(Permission(Threads::self()));
    }
    if (mode == PEG_SEM_READ && _readers.get() != 0)
        _readers--;
    else if (_writers.get() != 0)
        _writers--;
}

int ReadWriteSem::read_count() const
{
    return _readers.get();
}

int ReadWriteSem::write_count() const
{
    return _writers.get();
}

#endif /* PEGASUS_USE_POSIX_RWLOCK */

//==============================================================================
//
// PEGASUS_USE_SEMAPHORE_RWLOCK
//
//==============================================================================

#if defined(PEGASUS_USE_SEMAPHORE_RWLOCK)

// // If i get cancelled, I MUST ensure:
// 1) I do not hold the internal mutex
// 2) I do not hold the write lock
// 3) I am not using a reader slot

#if 0
void extricate_read_write(void *parm)
{
    ReadWriteSem *rws = (ReadWriteSem *) parm;
    ThreadType myself = Threads::self();

    if (Threads::equal(rws->_rwlock._wlock.get_owner(), myself))
        rws->_rwlock._wlock.unlock();
    else if (rws->_readers.get() > 0)
        rws->_rwlock._rlock.signal();

    if (Threads::equal(rws->_rwlock._internal_lock.get_owner(), myself))
        rws->_rwlock._internal_lock.unlock();
}
#endif


ReadWriteSem::ReadWriteSem():_readers(0), _writers(0), _rwlock()
{
}

ReadWriteSem::~ReadWriteSem()
{
    // lock everyone out of this object
    try
    {
        _rwlock._internal_lock.lock();
    }
    catch (Deadlock &)
    {
        // no problem - we own the lock, which is what we want
    }
    catch (IPCException &)
    {
        PEGASUS_ASSERT(0);
    }
    while (_readers.get() > 0 || _writers.get() > 0)
    {
        Threads::yield();
    }
    _rwlock._internal_lock.unlock();
}






//-----------------------------------------------------------------
// if milliseconds == -1, wait indefinately
// if milliseconds == 0, fast wait
//-----------------------------------------------------------------
void ReadWriteSem::timed_wait(Uint32 mode, ThreadType caller,