AOO410/main/unotools/inc/unotools/readwritemutexguard.hxx

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#ifndef INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
#define INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX

#include <osl/mutex.hxx>

namespace utl {

class ReadWriteGuard;
class ReadWriteMutex
{
    friend class ReadWriteGuard;

            sal_uInt32          nReadCount;
            sal_uInt32          nBlockCriticalCount;
            ::osl::Mutex*       pMutex;
            ::osl::Mutex*       pWriteMutex;

public:
                                ReadWriteMutex()
                                    : nReadCount(0)
                                    , nBlockCriticalCount(0)
                                    , pMutex( new ::osl::Mutex )
                                    , pWriteMutex( new ::osl::Mutex )
                                    {}
                                ~ReadWriteMutex()
                                    {
                                        delete pMutex;
                                        delete pWriteMutex;
                                    }
};


namespace ReadWriteGuardMode {
const sal_Int32 nWrite          = 0x01;
const sal_Int32 nCriticalChange = 0x02 | nWrite;
const sal_Int32 nBlockCritical  = 0x04;     // only a block, not a read, exclusive flag!
}

/** Enable multiple threads to read simultaneously, but a write blocks all
    other reads and writes, and a read blocks any write.
    Used in I18N wrappers to be able to maintain a single instance of a wrapper
    for the standard Office locale.
    NEVER construct a writing guard if there is already a reading guard in the
    same context, the following will dead lock EVEN IN THE SAME THREAD!
    void foo()
    {
        ReadWriteGuard aGuard1( aMutex );
        bar();
    }
    void bar()
    {
        // waits forever for aGuard1
        ReadWriteGuard aGuard2( aMutex, ReadWriteGuardMode::nWrite );
    }
 */
class ReadWriteGuard
{
            ReadWriteMutex&     rMutex;
            sal_Int32           nMode;
public:
                                ReadWriteGuard(
                                    ReadWriteMutex& rMutex,
                                    sal_Int32 nRequestMode = 0  // read only
                                    );
                                ~ReadWriteGuard();

    /** Be careful with this, it does wait for ANY read to complete.
        The following will dead lock EVEN IN THE SAME THREAD!
        void foo()
        {
            ReadWriteGuard aGuard1( aMutex );
            bar();
        }
        void bar()
        {
            ReadWriteGuard aGuard2( aMutex );
            aGuard2.changeReadToWrite();    // waits forever for aGuard1
        }
     */
            void                changeReadToWrite();
};

}   // namespace utl

#endif // INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX