Evolution never stops, even on sample code :-)
As such, I'd like to insert minor changes on the previous coding.
Check out sample outputs for both ISM and DISM experiments.
The sample learning code below is using the SHM_SHARE_MMU flag to ::shmat() which is for ISM, but exactly the same code can be used replacing the flag for SHM_PAGEABLE (DISM) or 0 (System V Shared Memory).
Don't forget to compile it for 64-bits (-m64) if you want segments larger than 4 GB. This version has a crude pause() routine to avoid relying on a debugger.
001: /*
002: * File: main.cpp
003: * Author: AZ
004: *
005: * Created on June 4, 2013, 7:31 AM
006: *
007: */
008:
009: #include <iostream>
010:
011: #include <sys/ipc.h>
012: #include <sys/shm.h>
013:
014: #include <sys/mman.h>
015: #include <errno.h>
016:
017: void pause( char const * message )
018: {
019: std::cout << message << std::endl
<< "Press <ENTER> to continue...";
020: std::cin.get( );
021: }
022:
023: void success( )
024: {
025: std::cout << "Success!" << std::endl
<< std::endl;
026: }
027:
028: void failure( )
029: {
030: std::cout << "Failure!" << std::endl
<< std::endl;
031: }
032:
033: int main( )
034: {
035: pause( "Getting shared memory." );
036:
037: std::size_t const size =
1UL * 1024UL * 1024UL * 1024UL;
038:
039: int id =
::shmget( 1, size, IPC_CREAT | IPC_EXCL |
SHM_R | SHM_W | ( SHM_R >> 3 ) | ( SHM_W >> 3 ) );
040:
041: if ( id == -1 )
042: {
043: failure( );
044: }
045: else
046: {
047: success( );
048:
049: pause( "Attaching to shared memory." );
050:
051: void * p = ::shmat( id, 0, SHM_SHARE_MMU );
052:
053: if ( reinterpret_cast < intptr_t > ( p ) == -1 )
054: {
055: failure( );
056: }
057: else
058: {
059: success( );
060:
061: pause( "Locking shared memory." );
062:
063: if ( ::mlock( p, size ) == 0 )
064: {
065: success( );
066:
067: pause( "Using shared memory." );
068:
069: ::memset( p, '*', size );
070:
071: success( );
072:
073: pause( "Unlocking shared memory." );
074:
075: switch ( ::munlock( p, size ) )
076: {
077: case 0:
078: success( );
079: break;
080:
081: case -1:
082: failure( );
083: break;
084: }
085:
086: }
087: else
088: {
089: ::perror( 0 );
090:
091: failure( );
092: }
093:
094: pause( "Detaching shared memory." );
095:
096: switch ( ::shmdt( p ) )
097: {
098: case 0:
099: success( );
100: break;
101:
102: case -1:
103: failure( );
104: break;
105: }
106: }
107:
108: pause( "Removing shared memory." );
109:
110: switch ( ::shmctl( id, IPC_RMID, 0 ) )
111: {
112: case 0:
113: success( );
114: break;
115:
116: case -1:
117: failure( );
118: break;
119: }
120: }
121:
122: pause( "Exiting program." );
123:
124: return 0;
125: }
