interprocess communication-Shared memory

• void *mmap (void *addr,size_t len,int prot,int flags, int fd,off_t offset);
  • Prot: Protection method
  • Prot_read: Page readable
  • Prot_write: Page writable
  • Prot_exec:
  • Prot_none:
  • Fiags:
  • Map_shared:
  • Map_private: The change is private
  • Map_fixed: Accurate explanation of addr
  • Map_anonymous: Set up anonymous mappings, no files involved
  • Mmap is to reverse the memory in a page, memory is an integer multiple of the page
• int munmmap (int fd,size_t size)
• int Msync (void *addr, size_t len,int flags)
  • Flags
    • Ms_anync: Performing asynchronous writes
    • Ms_sync: Performing Synchronous writes
    • MS_INVALIDATR: Cache is invalid
• Attention
  • The map cannot change the size of the file
• Give me a chestnut.

  • 1 //Create shared Memory2#include <sys/mman.h>3#include <unistd.h>4#include <sys/types.h>5 6#include <stdlib.h>7#include <stdio.h>8#include <errno.h>9#include <sys/stat.h>Ten#include <fcntl.h> One  A #defineErr_exit (M) -      Do -     { the perror (m); - exit (exit_failure); -} while(0) -  +typedefstructSTT - { +     Charname[4]; A     intAge ; at }stu; -  - intMainintargcChar*argv[]) - { -     if(ARGC! =2) -     { in exit (exit_failure); -     } to  +     intFD; -FD = open (argv[1], O_creat | O_rdwr | O_trunc,0666); the     if(FD = =-1) *     { $Err_exit ("Open");Panax Notoginseng     } -Lseek (FD,sizeof(STU) *5-1, seek_set); theWrite (FD,"",1); +STU *p; Ap = (stu*) mmap (NULL,sizeof(STU) *5, Prot_read | PROT_WRITE,MAP_SHARED,FD,0); the     if(p = =NULL) +Err_exit ("mmap"); -     CharCH ='a'; $     inti; $      for(i =0;i<5; i++) -     { -memcpy (p+i)->name,&ch,1); the(p+i)->age= -+i;  -ch++;Wuyi     } theprintf"initlize over!\n"); -Munmap (P,sizeof(STU) *5); Wuprintf"exit....\n");  -     return 0; About}

  • 1 //Read Shared memory2#include <sys/mman.h>3#include <unistd.h>4#include <sys/types.h>5 6#include <stdlib.h>7#include <stdio.h>8#include <errno.h>9#include <sys/stat.h>Ten#include <fcntl.h> One  A #defineErr_exit (M) -      Do -     { the perror (m); - exit (exit_failure); -} while(0) -  +typedefstructSTT - { +     Charname[4]; A     intAge ; at }stu; -  - intMainintargcChar*argv[]) - { -     if(ARGC! =2) -     { in exit (exit_failure); -     } to  +     intFD; -FD = open (argv[1], O_RDWR); the     if(FD = =-1) *     { $Err_exit ("Open");Panax Notoginseng     } -  theSTU *p; +p = (stu*) mmap (NULL,sizeof(STU) *5, Prot_read | PROT_WRITE,MAP_SHARED,FD,0); A     if(p = =NULL) theErr_exit ("mmap"); +     CharCH ='a'; -     inti; $      for(i =0;i<5; i++) $     { -printf"name =%s, age =%d\n", (P+i)->name, (P+i),Age ); -     } theMunmap (P,sizeof(STU) *5); -printf"exit....\n"); Wuyi     return 0; the}

• System v Shared Memory

  • Persist with the kernel (same message queue)

  • 1 //Shared Memory Functions2#include <sys/ipc.h>3#include <sys/shm.h>4 5 //Create or access a shared memory6 intShmget (key_t key,size_t size,intSHMFLG);7 //Mapping8 void* Shmat (intShmid,Const void*SHMADDR,intSHMFLG);9 //detachedTen intSHMDT (Const void*shmaddr); One //Control A intShmctl (intShimid,intCmdstructShmid_ds *buf);

interprocess communication-Shared memory