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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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