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// $Id: Semaphores_2.cpp 91671 2010-09-08 18:39:23Z johnnyw $
// Illustrates the use of the ACE_SV_Semaphore_Complex class and the
// ACE_Malloc class using the ACE_Shared_Memory_Pool (which uses
// System V shared memory). Note that it doesn't matter whether the
// parent or the child creates the semaphore since Semaphore_Complex
// will correctly serialize the intialization of the mutex and synch
// objects.
#include "ace/Malloc_T.h"
#include "ace/Shared_Memory_Pool.h"
#include "ace/SV_Semaphore_Complex.h"
#include "ace/OS_NS_unistd.h"
#if defined (ACE_HAS_SYSV_IPC) && !defined(ACE_LACKS_SYSV_SHMEM)
// Shared memory allocator (note that this chews up the
// ACE_DEFAULT_SEM_KEY).
static ACE_Malloc<ACE_SHARED_MEMORY_POOL, ACE_SV_Semaphore_Simple> my_alloc;
const int SEM_KEY_1 = ACE_DEFAULT_SEM_KEY + 1;
const int SEM_KEY_2 = ACE_DEFAULT_SEM_KEY + 2;
static int
parent (char *shm)
{
char *s = shm;
// Both semaphores are initially created with a count of 0, i.e.,
// they are "locked."
ACE_SV_Semaphore_Complex mutex (SEM_KEY_1, ACE_SV_Semaphore_Complex::ACE_CREATE, 0);
ACE_SV_Semaphore_Complex synch (SEM_KEY_2, ACE_SV_Semaphore_Complex::ACE_CREATE, 0);
// This is a critical section, which is protected by the mutex
// semaphore.
for (char c = 'a'; c <= 'z'; c++)
*s++ = c;
*s = '\0';
if (mutex.release () == -1)
ACE_ERROR ((LM_ERROR, "%p", "parent mutex.release"));
else if (synch.acquire () == -1)
ACE_ERROR ((LM_ERROR, "%p", "parent synch.acquire"));
if (my_alloc.remove () == -1)
ACE_ERROR ((LM_ERROR, "%p\n", "my_alloc.remove"));
if (mutex.remove () == -1)
ACE_ERROR ((LM_ERROR, "%p\n", "mutex.remove"));
if (synch.remove () == -1)
ACE_ERROR ((LM_ERROR, "%p\n", "synch.remove"));
return 0;
}
static int
child (char *shm)
{
// Both semaphores are initially created with a count of 0, i.e.,
// they are "locked."
ACE_SV_Semaphore_Complex mutex (SEM_KEY_1, ACE_SV_Semaphore_Complex::ACE_CREATE, 0);
ACE_SV_Semaphore_Complex synch (SEM_KEY_2, ACE_SV_Semaphore_Complex::ACE_CREATE, 0);
// Perform "busy waiting" here until we acquire the semaphore. This
// isn't really a good design -- it's just to illustrate that you
// can do non-blocking acquire() calls with the ACE System V
// semaphore wrappers.
while (mutex.tryacquire () == -1)
if (errno == EAGAIN)
ACE_DEBUG ((LM_DEBUG, "spinning in child!\n"));
else
ACE_ERROR_RETURN ((LM_ERROR, "child mutex.tryacquire"), 1);
for (char *s = (char *) shm; *s != '\0'; s++)
ACE_DEBUG ((LM_DEBUG, "%c", *s));
ACE_DEBUG ((LM_DEBUG, "\n"));
if (synch.release () == -1)
ACE_ERROR_RETURN ((LM_ERROR, "child synch.release"), 1);
return 0;
}
int
ACE_TMAIN (int, ACE_TCHAR *[])
{
char *shm = (char *) my_alloc.malloc (27);
switch (ACE_OS::fork ())
{
case -1:
ACE_ERROR_RETURN ((LM_ERROR, "fork failed\n"), -1);
/* NOTREACHED */
case 0:
// Child.
return child (shm);
default:
return parent (shm);
}
}
#else
int ACE_TMAIN (int, ACE_TCHAR *[])
{
ACE_ERROR ((LM_ERROR,
"SYSV IPC, or SYSV SHMEM is not supported on this platform\n"));
return 0;
}
#endif /* ACE_HAS_SYSV_IPC */
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