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Rusty · Guest

Hi,

I needed synchronised iterators on STL containers. Unable to find some
standard or popular implementation, I have written something myself.

It would be great if it can be reviewed and any mistakes pointed out
Smile

.

Thanks,

Regards,
Aseem.

/**
* This class attempts to provide synchronised STL like iterators.
* It assumes following inputs and behaviours:
*
* 1. All operations on the container will be done under some mutex.
* 2. Mutex class will provide Lock datatype type whose constructor
will acquire
* mutex and destructor will release mutex.
*
* For more clarity see the usage of lock in the Iterator class.
* 3. If the object pointed by the iterator at present has been removed
from
* container, it is assumed that some boolean predicate will be
provided as
* input which will take object as input and return a boolean
* which indicats that object has been removed (false) or not
(true).
* 4. A dereference functor will be provided which will return object
given iterator
* of type container.
* 5. Default Dereference and IsValid are given below.
*/
#ifndef _SYNC_STL_ITERATORS_H
#define _SYNC_STL_ITERATORS_H

#include<iterator>
#include<lib/Mutex.h>

template<class T>
class IsValid
{
public:
bool operator() (T t)
{
return (t->isValid ());
}
};

template<class Container, class T>
class MapValue
{
public:
typedef typename Container::iterator Iterator;

typedef typename Container::value_type ValueType;

T operator() (Iterator it)
{
return it->second;
}

T operator() (const ValueType& value)
{
return value.second;
}
};

/*
* we have to redeclare iterator struct here because:
*
* 1. In host platform, this struct is always defined.
* 2. In target platform, this struct is defined only under flag
__STL_USE_NAMESPACES.
*
* .h files in question are :
*
* For host : /usr/include/g++-3/stl_iterator.h
* For target : /opt/eldk/ppc_8xx/usr/include/g++-3/stl_iterator.h
*
* therefore we have to define this struct if platform is target and
__STL_USE_NAMESPACES
* is not defined.
*/
#if !defined(EMULATOR) && !defined(__STL_USE_NAMESPACES)
template <class _Category, class _Tp, class _Distance = ptrdiff_t,
class _Pointer = _Tp*, class _Reference = _Tp&>
struct iterator {
typedef _Category iterator_category;
typedef _Tp value_type;
typedef _Distance difference_type;
typedef _Pointer pointer;
typedef _Reference reference;
};
#endif

template<class T, class Container, class Dereference =
MapValue<Container, T>,
class MutexClass = Mutex, class Predicate = IsValid<T> >
class iteratorT : public iterator<forward_iterator_tag, T>
{
private:
typedef typename Container::iterator mIter;

typedef typename MutexClass::Lock Lock;

mIter position;

Container& mInstances;

MutexClass& mMutex;

T object;

Predicate mPred;

Dereference mDereference;

inline void setNull ()
{
object = T (NULL);
}

inline bool isEnd ()
{
return (position == mInstances.end ());
}

inline void increment ()
{
if ((object) && mPred (object)) {
init (++position);
} else {
init (mInstances.end ());
}
}

inline void init (const mIter& it)
{
position = it;

if (isEnd ()) {
setNull ();
} else {
object = mDereference (position);
}
}
public:
typedef const T ReturnType;

typedef iteratorT<T, Container, Dereference, MutexClass,
Predicate> SelfType;

iteratorT (const mIter& it,
Container& instances,
MutexClass& m)
: mInstances (instances), mMutex (m),
mPred (IsValid<T> ()), mDereference (MapValue<Container,
T> ())
{
init (it);
}

iteratorT (const mIter& it, Container& instances, Mutex& m,
Predicate p,
Dereference dereference)
: mInstances (instances), mMutex (m),
mPred (p), mDereference (dereference)
{
init (it);
}

SelfType& operator= (const SelfType& other)
{
init (other.position);
}

bool operator== (const SelfType& other) const
{
return (object == other.object);
}

ReturnType operator*() const { return object; }

SelfType& operator++()
{
{
Lock lock (mMutex);

increment ();
}
return *this;
};

SelfType operator++(int)
{
iteratorT temp = *this;

{
Lock lock (mMutex);

increment ();
}
return temp;
}
};

#endif //_SYNC_STL_ITERATORS_H

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David Abrahams · Guest

"Rusty" <r_aseem (AT) yahoo (DOT) co.in> writes: