我正在为共享内存上的学生制作一个教程。不过，我在等待或发布信号时看到崩溃。我正在使用sem_open API来初始化信号量。在做sem_open之前我需要分配一些内存吗？它在我看来是一个分段错误。你能帮我吗？我可以在下面的程序中使用sem_open，但是我在这里看到崩溃？

#include

#include

#include

#include

#include

/** page size **/

#include

/** memcpy **/

#include

#include

#include

using namespace std;

class READER_WRITER_A

{

private:

string msg;

void *shm_ptr;

int shm_id;

sem_t *sem_rw;

void Init_Shm();

void Init_Sem();

public:

void Read_Msg();

void Write_Msg(string s1);

READER_WRITER_A();

};

void READER_WRITER_A::Init_Shm()

{

key_t key;

key = ftok("/home/joshis1/Downloads/IPC-BLOG/shm",1);

shm_id = shmget(key, getpagesize(), IPC_CREAT| 0660);

shm_ptr = shmat(shm_id, NULL, 0660);

}

void READER_WRITER_A::Init_Sem()

{

sem_rw = sem_open("/home/joshis1/Downloads/IPC-BLOG/rw_sem", O_RDWR | O_CREAT, 0666, 0);

cout<

if(sem_rw < 0)

cout<

sem_post(sem_rw);

cout<

}

void READER_WRITER_A::Read_Msg()

{

//sem_wait(sem_rw);

int *size = (int *)shm_ptr;

void *msg_ptr = shm_ptr;

msg_ptr+=sizeof(int);

cout<

memcpy(&msg,(string *)msg_ptr,*size);

cout<

//sem_post(sem_rw);

}

void READER_WRITER_A::Write_Msg(string s1)

{

//sem_wait(sem_rw);

void *msg_ptr = shm_ptr;

msg = s1;

int *pt = (int*)shm_ptr;

*pt = s1.size();

cout<

msg_ptr+=sizeof(int);

cout<

memcpy((string *)msg_ptr,&msg,s1.size());

//sem_post(sem_rw);

}

READER_WRITER_A::READER_WRITER_A()

{

Init_Shm();

Init_Sem();

}

int main(int argc, char *argv[])

{

READER_WRITER_A val;

val.Write_Msg("I am A-RW");

val.Read_Msg();

return 0;

}

这是输出。

$ ./reader_writer_a.out

Sem_Post calling

Segmentation fault (core dumped)

这里分析coredump。

(gdb) bt

#0 0x0000003fb060d790 in sem_post() from /lib64/libpthread.so.0

#1 0x0000000000400fd0 in READER_WRITER_A::Init_Sem (this=0x7fff50e322a0) at reader_writer_a.cpp:52

#2 0x0000000000401199 in READER_WRITER_A::READER_WRITER_A (this=0x7fff50e322a0) at reader_writer_a.cpp:86

#3 0x00000000004011d8 in main (argc=1, argv=0x7fff50e323c8) at reader_writer_a.cpp:92