source: box/trunk/lib/common/NamedLock.cpp @ 2536

// --------------------------------------------------------------------------
//
// File
//              Name:    NamedLock.cpp
//              Purpose: A global named lock, implemented as a lock file in
//                       file system
//              Created: 2003/08/28
//
// --------------------------------------------------------------------------

#include "Box.h"

#include <fcntl.h>
#include <errno.h>

#ifdef HAVE_UNISTD_H
        #include <unistd.h>
#endif

#ifdef HAVE_FLOCK
        #include <sys/file.h>
#endif

#include "NamedLock.h"
#include "CommonException.h"

#include "MemLeakFindOn.h"

// --------------------------------------------------------------------------
//
// Function
//              Name:    NamedLock::NamedLock()
//              Purpose: Constructor
//              Created: 2003/08/28
//
// --------------------------------------------------------------------------
NamedLock::NamedLock()
        : mFileDescriptor(-1)
{
}

// --------------------------------------------------------------------------
//
// Function
//              Name:    NamedLock::~NamedLock()
//              Purpose: Destructor (automatically unlocks if locked)
//              Created: 2003/08/28
//
// --------------------------------------------------------------------------
NamedLock::~NamedLock()
{
        if(mFileDescriptor != -1)
        {
                ReleaseLock();
        }
}

// --------------------------------------------------------------------------
//
// Function
//              Name:    NamedLock::TryAndGetLock(const char *, int)
//              Purpose: Tries to get a lock on the name in the file system.
//                       IMPORTANT NOTE: If a file exists with this name, it
//                       will be deleted.
//              Created: 2003/08/28
//
// --------------------------------------------------------------------------
bool NamedLock::TryAndGetLock(const std::string& rFilename, int mode)
{
        // Check
        if(mFileDescriptor != -1)
        {
                THROW_EXCEPTION(CommonException, NamedLockAlreadyLockingSomething)
        }

        // See if the lock can be got
#if HAVE_DECL_O_EXLOCK
        int fd = ::open(rFilename.c_str(),
                O_WRONLY | O_NONBLOCK | O_CREAT | O_TRUNC | O_EXLOCK, mode);
        if(fd != -1)
        {
                // Got a lock, lovely
                mFileDescriptor = fd;
                return true;
        }
        
        // Failed. Why?
        if(errno != EWOULDBLOCK)
        {
                // Not the expected error
                THROW_EXCEPTION(CommonException, OSFileError)
        }

        return false;
#else
        int fd = ::open(rFilename.c_str(), O_WRONLY | O_CREAT | O_TRUNC, mode);
        if(fd == -1)
        {
                BOX_WARNING("Failed to open lockfile: " << rFilename);
                THROW_EXCEPTION(CommonException, OSFileError)
        }

#ifdef HAVE_FLOCK
        if(::flock(fd, LOCK_EX | LOCK_NB) != 0)
        {
                ::close(fd);
                if(errno == EWOULDBLOCK)
                {
                        return false;
                }
                else
                {
                        THROW_EXCEPTION(CommonException, OSFileError)
                }
        }
#elif HAVE_DECL_F_SETLK
        struct flock desc;
        desc.l_type = F_WRLCK;
        desc.l_whence = SEEK_SET;
        desc.l_start = 0;
        desc.l_len = 0;
        if(::fcntl(fd, F_SETLK, &desc) != 0)
        {
                ::close(fd);
                if(errno == EAGAIN)
                {
                        return false;
                }
                else
                {
                        THROW_EXCEPTION(CommonException, OSFileError)
                }
        }
#endif

        // Success
        mFileDescriptor = fd;

        return true;
#endif
}

// --------------------------------------------------------------------------
//
// Function
//              Name:    NamedLock::ReleaseLock()
//              Purpose: Release the lock. Exceptions if the lock is not held
//              Created: 2003/08/28
//
// --------------------------------------------------------------------------
void NamedLock::ReleaseLock()
{
        // Got a lock?
        if(mFileDescriptor == -1)
        {
                THROW_EXCEPTION(CommonException, NamedLockNotHeld)
        }
        
        // Close the file
        if(::close(mFileDescriptor) != 0)
        {
                THROW_EXCEPTION(CommonException, OSFileError)
        }
        // Mark as unlocked
        mFileDescriptor = -1;
}