Bug on Posix IPC_STAT. Wrong number of attachments

[tcak via Digitalmars-d-learn]

I create a shared memory by using shmget. And attach to it by 
using shmat.

Finally, I use shmctl to get statistics to learn number of 
attachments to
that shared memory. According to documentation 
(linux.die.net/man/2/shmat), number of attachments should be 1.

Same codes, C returns 1, D returns 0. It took me 2 days until 
realising this.

I put C and D codes, and makefile for quick testing.

Ubuntu 64-bit. Kernel: 3.13.0-44-generic

I checked the shmid_ds at both "core.sys.posix.sys.shm" and 
"/usr/include/bits/shm.h". They look similar. Although C 
definition makes a difference based on 32 and 64 bits, D's 
definition doesn't care about. Because I am on 64-bit kernel, 
they should be same.



main.c
==========================
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <fcntl.h>

void main(){
        // allocate
	int id = shmget( IPC_PRIVATE, 4096, IPC_CREAT | S_IRUSR | 
S_IWUSR );

        // if failed, leave
        if( id == -1 ){
                printf("shmget failed\n");
                return;
        }

        // attach
        void* ptr = shmat( id, 0, 0 );

        // if failed, leave
        if( ptr == (void*)-1 ){
                printf("shmat failed\n");
                shmctl( id, IPC_RMID, 0 );
                return;
        }

        // stat
        struct shmid_ds stat;

        // get statistics
        int res = shmctl( id, IPC_STAT, &stat );
        printf("STAT: %d\n", res);

        // get number of attachments
        printf("NATTCH: %d\n", (unsigned short)stat.shm_nattch);

        // detach
        shmdt( ptr );

        // remove
        shmctl( id, IPC_RMID, 0 );
}


main.d
===============================
import std.stdio;

private import core.sys.posix.sys.mman;
private import core.sys.posix.sys.shm;
private import core.sys.posix.unistd;
private import core.sys.posix.sys.stat;
private static import core.stdc.errno;
private static import core.stdc.time;

void main(){
        // allocate
	int id = shmget( IPC_PRIVATE, 4096, IPC_CREAT | S_IRUSR | 
S_IWUSR );

        // if failed, leave
        if( id == -1 ){
                writeln("shmget failed");
                return;
        }

        // attach
        void* ptr = shmat( id, null, 0 );

        // if failed, leave
        if( ptr == cast(void*)-1 ){
                writeln("shmat failed");
                shmctl( id, IPC_RMID, null );
                return;
        }

        // stat
        shmid_ds stat;

        // get statistics
        int res = shmctl( id, IPC_STAT, &stat );
        writeln("STAT: ", res);

        // get number of attachments
        writeln("NATTCH: ", stat.shm_nattch);

        // detach
        shmdt( ptr );

        // remove
        shmctl( id, IPC_RMID, null );
}



makefile
==============================
all:
        dmd main.d -of"dprog"
        gcc main.c -o cprog

clear:
        rm cprog
        rm dprog