Re: [Boost-users] [Boost::Interprocess] access violation when function returns a pointer to shared memory object

Subject: Re: [Boost-users] [Boost::Interprocess] access violation when function returns a pointer to shared memory object
From: Casimiro, Daniel C CIV NUWC NWPT (daniel.casimiro_at_[hidden])
Date: 2009-10-22 09:13:25

I think that you are having a problem because your "segment" object has gone out of scope. I believe that the memory is unmapped at that point, and you are left with a dangling pointer.

~Dan 

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] 
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of BaDBuTz
> Sent: Thursday, October 22, 2009 5:32
> To: boost-users_at_[hidden]
> Subject: [Boost-users] [Boost::Interprocess] access violation 
> when function returns a pointer to shared memory object
> 
> hi, 
> 
> I want to synchronize multiple Processes with boost::Interprocess. 
> 
> For the start I implemented a simple Synchronisation Class 
> (with some mutexes) in my test program that will be stored in 
> the Shared Memory.
> 
> The first call of print() (in function getSyncObject) returns 
> the correct output. But why do I get an access violation, 
> when I call the function again (the pointer is the same!) in main()?
> 
> I am using WINXP, msvc 7-1 and mingw44 (with both compilers I 
> get the same error)
> 
> 
> Thanks in advance
> 
> Martin
> 
> 
> (compilable) Code:
> 
> #include <iostream>
> 
> #include <boost/interprocess/managed_shared_memory.hpp>
> #include <boost/interprocess/allocators/allocator.hpp>
> #include <boost/interprocess/containers/string.hpp>
> 
> 
> typedef unsigned long U32;
> 
> class SyncObject
>   {
>   public:
>     SyncObject(std::string aId) : id(aId),
>         locAddrSp0Range(0),
>         locAddrSp0Remap(0),
>         locAddrSp1Range(0),
>         locAddrSp1Remap(0),
>         usbInterfaceOwner(0),
>         useCounter(0)
>     {};
> 
>     ~SyncObject()
>     {}
>     ;
> 
> 	void print()
>     {
>       std::cout 
> 	  << id
>       << " locAddrSp0Range = " << locAddrSp0Range
>       << " locAddrSp0Remap = " << locAddrSp0Remap
>       << " locAddrSp1Range = " << locAddrSp1Range
>       << " locAddrSp1Remap = " << locAddrSp1Remap
>       << " usbInterfaceOwner = " << usbInterfaceOwner
>       << " useCounter = " << useCounter
>       << "\n";
>     };
> 
>     std::string id;
> 
>     boost::interprocess::interprocess_mutex mtxReadWrite;
>     boost::interprocess::interprocess_mutex mtxFunction;
> 
>     U32 locAddrSp0Range;
>     U32 locAddrSp0Remap;
>     U32 locAddrSp1Range;
>     U32 locAddrSp1Remap;
> 
>     U32 usbInterfaceOwner;
> 
>     U32 useCounter;
>   };
> 
> 
> 
> class SharedMemory
>   {
>   public:
>     SharedMemory();
>     ~SharedMemory();
> 
>     SyncObject* getSyncObject(std::string id);
>   };
> 
> 
> using namespace boost::interprocess;
> 
> const char* MANAGED_SHARED_MEMORY_NAME = "sharedMemoryMapTest17";
> 
> 
> SharedMemory::SharedMemory()
> {}
> 
> SharedMemory::~SharedMemory()
> {}
> 
> SyncObject* SharedMemory::getSyncObject(std::string id) {
>   managed_shared_memory segment(open_or_create, 
> MANAGED_SHARED_MEMORY_NAME, 65536);
> 
>   SyncObject* ptr = 
> segment.construct<SyncObject>(anonymous_instance)(id);
> 	
>   ptr->print();  //works!
>   return ptr;
> }
> 
> 
> int main()
> {
>   SharedMemory shm;
>   SyncObject* ptr = shm.getSyncObject("idName");
> 
>   ptr->print(); //Application crashes here with an access violation
> 
>   return 0;
> }
> 
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