Programming Forums > Application Development > C++

rwm · Jul 3rd, 2007, 10:29 AM

heya,

im writing a plugin for maya, and well ive run into a problem that appears to be multiple inheritance...

what would you think the problem was:

(Toggle Plain Text)

#pragma once

#include <maya/MPxFileTranslator.h>

class Parser {
	public:
		Parser() {
			cout << "Parser::Parser()" << endl;
			file = 0;
			cout << "end Parser::Parser()" << endl;
		}
		virtual ~Parser() {
			cout << "Parser::~Parser()" << endl;
			Cleanup();
			cout << "end Parser::~Parser()" << endl;
		}
		void Cleanup() {
			cout << "Parser::Cleanup()" << endl;
			delete[] file;
			file = 0;
			cout << "end Parser::Cleanup()" << endl;
		}
	private:
		char *file;
};

class ParserTranslator : public Parser,public MPxFileTranslator {
	public:
		ParserTranslator() : Parser() {
			cout << "ParserTranslator::ParserTranslator()" << endl;
			cout << "end ParserTranslator::ParserTranslator()" << endl;
		}
		~ParserTranslator() {
			cout << "ParserTranslator::~ParserTranslator()" << endl;
			cout << "end ParserTranslator::~ParserTranslator()" << endl;
		}
		static void *creator() {
			return new ParserTranslator;
		}
	private:
		//
};

(Toggle Plain Text)

Parser::Parser()
end Parser::Parser()
ParserTranslator::ParserTranslator()
end ParserTranslator::ParserTranslator()
ParserTranslator::~ParserTranslator()
end ParserTranslator::~ParserTranslator()
Parser::~Parser()
Parser::Cleanup()
end Parser::Cleanup()
end Parser::~Parser()
*** glibc detected *** /usr/aw/maya/bin/maya.bin: double free or corruption (fasttop): 0x0a7260f0 ***

hope someone can help! im confused!

this shouldnt be happening???

EDIT:

just removed the comments so you might be more inclined to read it!

(Toggle Plain Text)

#pragma once

#include <maya/MPxFileTranslator.h>

class Parser {
	public:
		Parser() {
			file = 0;
		}
		virtual ~Parser() {
			Cleanup();
		}
		void Cleanup() {
			delete[] file;
			file = 0;
		}
	private:
		char *file;
};

class ParserTranslator : public Parser,public MPxFileTranslator {
	public:
		ParserTranslator() : Parser() {}
		~ParserTranslator() {}
		static void *creator() {
			return new ParserTranslator;
		}
	private:
		//
};

rwm · Jul 4th, 2007, 3:44 AM

i got a reply on the maya boards saying multiple inheritance is generally a bad idea in this case... any suggestions?

rwm · Jul 4th, 2007, 10:33 AM

ok, i wrote a custom wrapper so i could overload new/delete operators...

(Toggle Plain Text)

typedef Wrapper<int> Int;

class Parser {
	public:
		Parser() {
			p = 0;
		}
		Parser(int i) {
			p = new Int(i);
			cout << *p << endl;
		}
		virtual ~Parser() {
			Cleanup();
		}
		void Cleanup() {
			delete p;
			p = 0;
		}
	private:
		Int *p;
};

class ParserTranslator : public Parser,public MPxFileTranslator {
	public:
		ParserTranslator() : Parser(101) {
		}
		~ParserTranslator() {
		}
		static void *creator() {
			return new ParserTranslator;
		}
	private:
		//
};

and the output is

(Toggle Plain Text)

allocated 4 bytes (0x9d9d8c8)
101
deallocating (0x9478f70)
*** glibc detected *** /usr/aw/maya/bin/maya.bin: double free or corruption (fasttop): 0x09478f70 ***

its obviously freeing the wrong memory, but why?

if we look at the order of destruction it appears to be:

(Toggle Plain Text)

~ParserTranslator
~Parser

then i assume

(Toggle Plain Text)

~MPxFileTranslator

so i suppose that its destructing in the wrong order then?

any suggestions? please help!

rwm · Jul 4th, 2007, 10:46 AM

ive tested a similar inheritance in standard code, in this case i dont know what BaseB does (substitute for MPxFileTranslator) - in this case the only thing i can think of is that there is some sort of error in MPxFileTranslator???

(Toggle Plain Text)

#include <iostream>
using namespace std;

...

typedef Wrapper<int> Int;

class BaseA {
	public:
		BaseA() {
			p = 0;
		}
		BaseA(int i) {
			p = new Int(i);
			cout << *p << endl;
		}
		virtual ~BaseA() {
			Cleanup();
		}
		void Cleanup() {
			delete p;
			p = 0;
		}
	private:
		Int *p;
};

class BaseB {
	public:
		BaseB() {}
		~BaseB() {}
};

class Derived : public BaseA,public BaseB {
	public:
		Derived() : BaseA(101) {}
		~Derived() {}
};

int main() {
	//
	Derived der;

	return 0;
}

and the result is

(Toggle Plain Text)

allocated 4 bytes (0x8351008)
101
deallocating (0x8351008)

am i missing a key point here? or am i doing the stupidest thing on this planet?

rwm · Jul 5th, 2007, 4:55 AM

ah well i just found out that the plugin resides in its own memory space i.e. its a dll/so and my Parser class resides in its own memory space... hence invalid memory being freed...

i have a question, how can you make sure that memory of base classes resides in the dll/so space?

please help! puuuuuuhhhhhlllllllllllleeeeeeeeeeeaaaaaaaaaaaaaasssssssssssssseeeeeee!

rwm · Jul 5th, 2007, 5:09 AM

i found this on google:

To overcome the seperate heap problem you can make the destructor and all other functions that allocate/free memory of those objects that will be used across dll boundaries virtual. That way the object's "original" destructor/function will be called via the vtbl rather than the local one. So all will happen on the heap where the object was allocated.

(Toggle Plain Text)

class Parser {
	public:
		Parser() {
			p = 0;
		}
		Parser(int i) {
			p = new Wrapper<int>(i);
			cout << *p << endl;
		}
		virtual ~Parser() {
			Cleanup();
		}
		virtual void Cleanup() {
			delete p;
			p = 0;
		}
	private:
		Int *p;
};

same problem...

Jul 3rd, 2007, 10:29 AM	#1
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	multiple inheritance problem heya, im writing a plugin for maya, and well ive run into a problem that appears to be multiple inheritance... what would you think the problem was: (Toggle Plain Text) #pragma once #include <maya/MPxFileTranslator.h> class Parser { public: Parser() { cout << "Parser::Parser()" << endl; file = 0; cout << "end Parser::Parser()" << endl; } virtual ~Parser() { cout << "Parser::~Parser()" << endl; Cleanup(); cout << "end Parser::~Parser()" << endl; } void Cleanup() { cout << "Parser::Cleanup()" << endl; delete[] file; file = 0; cout << "end Parser::Cleanup()" << endl; } private: char file; }; class ParserTranslator : public Parser,public MPxFileTranslator { public: ParserTranslator() : Parser() { cout << "ParserTranslator::ParserTranslator()" << endl; cout << "end ParserTranslator::ParserTranslator()" << endl; } ~ParserTranslator() { cout << "ParserTranslator::~ParserTranslator()" << endl; cout << "end ParserTranslator::~ParserTranslator()" << endl; } static void creator() { return new ParserTranslator; } private: // }; #pragma once #include <maya/MPxFileTranslator.h> class Parser { public: Parser() { cout << "Parser::Parser()" << endl; file = 0; cout << "end Parser::Parser()" << endl; } virtual ~Parser() { cout << "Parser::~Parser()" << endl; Cleanup(); cout << "end Parser::~Parser()" << endl; } void Cleanup() { cout << "Parser::Cleanup()" << endl; delete[] file; file = 0; cout << "end Parser::Cleanup()" << endl; } private: char file; }; class ParserTranslator : public Parser,public MPxFileTranslator { public: ParserTranslator() : Parser() { cout << "ParserTranslator::ParserTranslator()" << endl; cout << "end ParserTranslator::ParserTranslator()" << endl; } ~ParserTranslator() { cout << "ParserTranslator::~ParserTranslator()" << endl; cout << "end ParserTranslator::~ParserTranslator()" << endl; } static void creator() { return new ParserTranslator; } private: // }; (Toggle Plain Text) Parser::Parser() end Parser::Parser() ParserTranslator::ParserTranslator() end ParserTranslator::ParserTranslator() ParserTranslator::~ParserTranslator() end ParserTranslator::~ParserTranslator() Parser::~Parser() Parser::Cleanup() end Parser::Cleanup() end Parser::~Parser() * glibc detected * /usr/aw/maya/bin/maya.bin: double free or corruption (fasttop): 0x0a7260f0 * Parser::Parser() end Parser::Parser() ParserTranslator::ParserTranslator() end ParserTranslator::ParserTranslator() ParserTranslator::~ParserTranslator() end ParserTranslator::~ParserTranslator() Parser::~Parser() Parser::Cleanup() end Parser::Cleanup() end Parser::~Parser() * glibc detected * /usr/aw/maya/bin/maya.bin: double free or corruption (fasttop): 0x0a7260f0 * hope someone can help! im confused! this shouldnt be happening??? EDIT: just removed the comments so you might be more inclined to read it! (Toggle Plain Text) #pragma once #include <maya/MPxFileTranslator.h> class Parser { public: Parser() { file = 0; } virtual ~Parser() { Cleanup(); } void Cleanup() { delete[] file; file = 0; } private: char file; }; class ParserTranslator : public Parser,public MPxFileTranslator { public: ParserTranslator() : Parser() {} ~ParserTranslator() {} static void creator() { return new ParserTranslator; } private: // }; #pragma once #include <maya/MPxFileTranslator.h> class Parser { public: Parser() { file = 0; } virtual ~Parser() { Cleanup(); } void Cleanup() { delete[] file; file = 0; } private: char file; }; class ParserTranslator : public Parser,public MPxFileTranslator { public: ParserTranslator() : Parser() {} ~ParserTranslator() {} static void creator() { return new ParserTranslator; } private: // };

Jul 4th, 2007, 10:33 AM	#3
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	ok, i wrote a custom wrapper so i could overload new/delete operators... (Toggle Plain Text) typedef Wrapper<int> Int; class Parser { public: Parser() { p = 0; } Parser(int i) { p = new Int(i); cout << p << endl; } virtual ~Parser() { Cleanup(); } void Cleanup() { delete p; p = 0; } private: Int p; }; class ParserTranslator : public Parser,public MPxFileTranslator { public: ParserTranslator() : Parser(101) { } ~ParserTranslator() { } static void creator() { return new ParserTranslator; } private: // }; typedef Wrapper<int> Int; class Parser { public: Parser() { p = 0; } Parser(int i) { p = new Int(i); cout << p << endl; } virtual ~Parser() { Cleanup(); } void Cleanup() { delete p; p = 0; } private: Int p; }; class ParserTranslator : public Parser,public MPxFileTranslator { public: ParserTranslator() : Parser(101) { } ~ParserTranslator() { } static void creator() { return new ParserTranslator; } private: // }; and the output is (Toggle Plain Text) allocated 4 bytes (0x9d9d8c8) 101 deallocating (0x9478f70) * glibc detected * /usr/aw/maya/bin/maya.bin: double free or corruption (fasttop): 0x09478f70 * allocated 4 bytes (0x9d9d8c8) 101 deallocating (0x9478f70) * glibc detected * /usr/aw/maya/bin/maya.bin: double free or corruption (fasttop): 0x09478f70 * its obviously freeing the wrong memory, but why? if we look at the order of destruction it appears to be: (Toggle Plain Text) ~ParserTranslator ~Parser ~ParserTranslator ~Parser then i assume (Toggle Plain Text) ~MPxFileTranslator ~MPxFileTranslator so i suppose that its destructing in the wrong order then? any suggestions? please help!

Jul 4th, 2007, 10:46 AM	#4
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	ive tested a similar inheritance in standard code, in this case i dont know what BaseB does (substitute for MPxFileTranslator) - in this case the only thing i can think of is that there is some sort of error in MPxFileTranslator??? (Toggle Plain Text) #include <iostream> using namespace std; ... typedef Wrapper<int> Int; class BaseA { public: BaseA() { p = 0; } BaseA(int i) { p = new Int(i); cout << p << endl; } virtual ~BaseA() { Cleanup(); } void Cleanup() { delete p; p = 0; } private: Int p; }; class BaseB { public: BaseB() {} ~BaseB() {} }; class Derived : public BaseA,public BaseB { public: Derived() : BaseA(101) {} ~Derived() {} }; int main() { // Derived der; return 0; } #include <iostream> using namespace std; ... typedef Wrapper<int> Int; class BaseA { public: BaseA() { p = 0; } BaseA(int i) { p = new Int(i); cout << p << endl; } virtual ~BaseA() { Cleanup(); } void Cleanup() { delete p; p = 0; } private: Int p; }; class BaseB { public: BaseB() {} ~BaseB() {} }; class Derived : public BaseA,public BaseB { public: Derived() : BaseA(101) {} ~Derived() {} }; int main() { // Derived der; return 0; } and the result is (Toggle Plain Text) allocated 4 bytes (0x8351008) 101 deallocating (0x8351008) allocated 4 bytes (0x8351008) 101 deallocating (0x8351008) am i missing a key point here? or am i doing the stupidest thing on this planet?

Jul 5th, 2007, 5:09 AM	#6
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	i found this on google: To overcome the seperate heap problem you can make the destructor and all other functions that allocate/free memory of those objects that will be used across dll boundaries virtual. That way the object's "original" destructor/function will be called via the vtbl rather than the local one. So all will happen on the heap where the object was allocated. (Toggle Plain Text) class Parser { public: Parser() { p = 0; } Parser(int i) { p = new Wrapper<int>(i); cout << p << endl; } virtual ~Parser() { Cleanup(); } virtual void Cleanup() { delete p; p = 0; } private: Int p; }; class Parser { public: Parser() { p = 0; } Parser(int i) { p = new Wrapper<int>(i); cout << p << endl; } virtual ~Parser() { Cleanup(); } virtual void Cleanup() { delete p; p = 0; } private: Int p; }; same problem...

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Jul 4th, 2007, 3:44 AM	#2
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	i got a reply on the maya boards saying multiple inheritance is generally a bad idea in this case... any suggestions?

Jul 5th, 2007, 4:55 AM	#5
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	ah well i just found out that the plugin resides in its own memory space i.e. its a dll/so and my Parser class resides in its own memory space... hence invalid memory being freed... i have a question, how can you make sure that memory of base classes resides in the dll/so space? please help! puuuuuuhhhhhlllllllllllleeeeeeeeeeeaaaaaaaaaaaaaasssssssssssssseeeeeee!

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multiple inheritance problem