RAII object in constructor

Newsgroup: comp.lang.c++

Subject: RAII object in constructor

From: =?ISO-8859-1?Q?Marcel_M=FCller?= <news.5.maazl@...>

Date: Wed, 09 Oct 2013 22:48:50 +0200



I have a mutex lock that is implemented as RAII. I need to acquire the

mutex as long as the constructor runs. But for the /entire/ constructor

run not just the construction of the derived class.





Example:



#include <stdio.h>



// some mutex class

class Mutex

{

public:

// hold the Mutex (RAII)

struct Lock

{ Lock(Mutex& mtx)

{ puts("Lock()\n");

//...

}

~Lock()

{ puts("~Lock()\n");

//...

}

};

//...

};



// set of configuration parameters

struct Parameters

{ //...

};



class WorkerBase

{ //...

protected:

WorkerBase(const Parameters& params)

{ // do something with params...

}

};



class Worker : public WorkerBase

{

private:

static Parameters GlobalParams;

static Mutex ParamMtx; // protect the above



public:

// synchronized public access to the parameters

struct AccessParams : Mutex::Lock

{ AccessParams() : Mutex::Lock(ParamMtx) {}

operator Parameters&() { return GlobalParams; }

};



Worker() : WorkerBase(AccessParams())

{ AccessParams params; // !!! Mutex acquired twice!

// do something with params...

}

};



Parameters Worker::GlobalParams;

Mutex Worker::ParamMtx;



int main()

{ Worker worker;

// do something with worker...

}





As expected the mutex is acquired twice. But this is bad, since the idea

is to sample a consistent set of parameters and not to use one parameter

set for the base class and some other one for the derived class.



Any ideas how to solve this?





Marcel

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