shared memory problem Post: 302087520

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Operating Systems HP-UX shared memory problem Post 302087520 by Frank2004 on Saturday 2nd of September 2006 03:08:00 AM

09-02-2006

Registered User

shared memory problem

Hi, there
On HP-UX, there is a problem about shared memory. The code open the data file and use the "mmap" system call to map into the shared memory, when the contents are make changes, there is no effective on shared memory. The codes look like the following:

Code:

 ...
sysdb=shm_open(path,O_CREAT|O_RDWR,S_IRWXO|S_IRWXG|S_IRWXU);
if (sysdb==-1)
 {
   perror("main:shm_open system database error");
   exit(1);
 }
 if(ftruncate(sysdb,SYSDB_SIZE)==-1)
   {
      perror("main:ftruncate sysdb failure");
      exit(1);
   }
   sysdb_addr=(caddr_t)mmap(0,SYSDB_SIZE,PROT_READ|PROT_WRITE,MAP_SHARED,\
              sysdb,0);
   if(sysdb_addr==(caddr_t)-1)
   {
      perror("main:system database mmap error");
      exit(1);
   }
   sysdb_header=(DB_HEADER *)sysdb_addr;
  
  ...

on the above codes, when the data changes in the file specified by 'path',
the value pointed by 'sysdb_addr' is still original.
Anyone can give some suggestion? thanks.

Last edited by blowtorch; 09-05-2006 at 03:31 AM.. Reason: put in code tags

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LEARN ABOUT OSF1

shm_unlink

shm_unlink(3)						     Library Functions Manual						     shm_unlink(3)

NAME

       shm_unlink - Removes a shared memory object created by a call to the shm_open function (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <sys/mman.h>

       int shm_unlink (
       const char *name);

PARAMETERS

       *name   Points to the name of the shared memory object.

DESCRIPTION

       The  shm_unlink	function  removes the name of the shared memory object pointed to by name.  If this file descriptor is used by other func-
       tions, all references to the shared memory object are removed, but content removal is delayed until all open and mapped references  to  the
       shared memory object are removed.

RETURN VALUES

       On a successful call to the shm_unlink function, a value of 0 (zero) is returned.  Otherwise, a value of -1 is returned and errno is set to
       indicate the error.

ERRORS

       The shm_unlink function fails under the following conditions:

       [EACCES] 	   Permission to unlink the shared memory object is denied.

       [ENAMETOOLONG]	   The length of the name argument exceeds PATH_MAX, or a pathname component is longer than NAME_MAX while _POSIX_NO_TRUNC
			   is in effect.

       [ENOENT] 	   The named shared memory object does not exist.

RELATED INFORMATION

       Functions: close(2), mmap(2), munmap(2), shm_open(3)

       Guide to Realtime Programming delim off

																     shm_unlink(3)

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