在 Linux 中使用共享对象

#ifndef __COMMON_H__
#define __COMMON_H__
class A {
public:
int m_nA;
virtual void WhoAmI();
static void * m_sArena;
void * operator new (unsigned int);
};
class B : public A {
public:
int m_nB;
virtual void WhoAmI();
};
class C : virtual public A {
public:
int m_nC;
virtual void WhoAmI();
};
void GetObjects(A ** pA, B ** pB, C ** pC);
#endif //__COMMON_H__

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include <stdio.h>
#include <iostream>
#include "common.h"
void * A::m_sArena = NULL;
void * A::operator new (unsigned int size)
{
switch (size)
{
case sizeof(A):
return m_sArena;
case sizeof(B):
return (void *)((int)m_sArena + 1024);
case sizeof(C):
return (void *)((int)m_sArena + 2048);
default:
cerr << __FILE__ << ":" << __LINE__ << " Critical error" <<
endl;
}
}
void A::WhoAmI() {
cout << "Object type: A" << endl;
}
void B::WhoAmI() {
cout << "Object type: B" << endl;
}
void C::WhoAmI() {
cout << "Object type: C" << endl;
}
void GetObjects(A ** pA, B ** pB, C ** pC) {
*pA = (A *)A::m_sArena;
*pB = (B *)((int)A::m_sArena + 1024);
*pC = (C *)((int)A::m_sArena + 2048);
}
class Initializer {
public:
int m_shmid;
Initializer();
static Initializer m_sInitializer;
};
Initializer Initializer::m_sInitializer;
Initializer::Initializer()
{
key_t key = 1234;
bool bCreated = false;
m_shmid = shmget(key, 3*1024, 0666);
if (-1 == m_shmid) {
if (ENOENT != errno) {
cerr << __FILE__ << ":" << __LINE__ << " Critical error" <<
endl;
return;
}
m_shmid = shmget(key, 3*1024, IPC_CREAT | 0666);
if (-1 == m_shmid) {
cerr << __FILE__ << ":" << __LINE__ << " Critical error" <<
endl;
return;
}
cout << "Created the shared memory" << endl;
bCreated = true;
}
A::m_sArena = shmat(m_shmid, NULL, 0);
if (-1 == (int)A::m_sArena) {
cerr << __FILE__ << ":" << __LINE__ << " Critical error" <<
endl;
return;
}
if (bCreated) {
// Construct objects on the shared memory
A * pA;
pA = new A;
pA->m_nA = 1;
pA = new B;
pA->m_nA = 2;
pA = new C;
pA->m_nA = 3;
}
return;
}

#include "common.h"
#include <iostream>
#include <stdlib.h>
int main (int argc, char * argv[])
{
int jumpTo = 0;
if (1 < argc) {
jumpTo = strtol(argv[1], NULL, 10);
}
if ((1 > jumpTo) || (6 < jumpTo)) {
jumpTo = 1;
}
A * pA;
B * pB;
C * pC;
GetObjects(&pA, &pB, &pC);
cout << (int)pA << "/t";
cout << (int)pB << "/t";
cout << (int)pC << "/n";
switch (jumpTo) {
case 1:
cout << pA->m_nA << endl;
case 2:
pA->WhoAmI();
case 3:
cout << pB->m_nA << endl;
case 4:
pB->WhoAmI();
case 5:
cout << pC->m_nA << endl;
case 6:
pC->WhoAmI();
}
return 0;
}
#include <pthread.h>
void DoNothingCode() {
pthread_create(NULL, NULL, NULL, NULL);
}

ldd shm_client1
libpthread.so.0 => (0x4002d000)
libshm_server.so => (0x40042000)
libc.so.6 => (0x4005b000)
ld-linux.so.2 => (0x40000000)

ldd shm_client2
libshm_server.so => (0x40018000)
libpthread.so.0 => (0x40046000)
libc.so.6 => (0x4005b000)
ld-linux.so.2 => (0x40000000)

$ ./shm_client1
Created the shared memory
1073844224 1073845248 1073846272
1
Object type: A
2
Object type: B
3
Object type: C
$ ipcs
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x000004d2 2260997 sachin 666 3072 0
$ ./shm_client1
1073840128 1073841152 1073842176
1
Object type: A
2
Object type: B
->   0
->   Segmentation fault (core dumped)

$ ./shm_client1
Created the shared memory
1073844224 1073845248 1073846272
1
Object type: A
2
Object type: B
3
Object type: C
$ ipcs
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x000004d2 2359301 sachin 666 3072 0
$ ./shm_client2
1073942528 1073943552 1073944576
1
-> Segmentation fault (core dumped)
$ ./shm_client2 3
1073942528 1073943552 1073944576
2
-> Segmentation fault (core dumped)
$ ./shm_client2 5
1073942528 1073943552 1073944576
-> 1048594
-> Segmentation fault (core dumped)