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linux_man_pages_library

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/* map the object into the caller\(aqs address space. */
struct shmbuf *shmp = mmap(null, sizeof(*shmp),
prot_read | prot_write,
map_shared, fd, 0);
if (shmp == map_failed)
errexit("mmap");
/* initialize semaphores as process\-shared, with value 0. */
if (sem_init(&shmp\->sem1, 1, 0) == \-1)
errexit("sem_init\-sem1");
if (sem_init(&shmp\->sem2, 1, 0) == \-1)
errexit("sem_init\-sem2");
/* wait for \(aqsem1\(aq to be posted by peer before touching
shared memory. */
if (sem_wait(&shmp\->sem1) == \-1)
errexit("sem_wait");
/* convert data in shared memory into upper case. */
for (int j = 0; j < shmp\->cnt; j++)
shmp\->buf[j] = toupper((unsigned char) shmp\->buf[j]);
/* post \(aqsem2\(aq to tell the peer that it can now
access the modified data in shared memory. */
if (sem_post(&shmp\->sem2) == \-1)
errexit("sem_post");
/* unlink the shared memory object. even if the peer process
is still using the object, this is okay. the object will
be removed only after all open references are closed. */
shm_unlink(shmpath);
exit(exit_success);
}
.ee
.in
.\"
.ss program source: pshm_ucase_send.c
the "send" program takes two command-line arguments:
the pathname of a shared memory object previously created by the "bounce"
program and a string that is to be copied into that object.
.pp
the program opens the shared memory object
and maps the object into its address space.
it then copies the data specified in its second argument
into the shared memory,
and posts the first semaphore,
which tells the "bounce" program that it can now access that data.
after the "bounce" program posts the second semaphore,
the "send" program prints the contents of the shared memory
on standard output.
.pp
.in +4n
.ex
/* pshm_ucase_send.c
licensed under gnu general public license v2 or later.
*/
#include <string.h>
#include "pshm_ucase.h"
int
main(int argc, char *argv[])
{
if (argc != 3) {
fprintf(stderr, "usage: %s /shm\-path string\en", argv[0]);
exit(exit_failure);
}
char *shmpath = argv[1];
char *string = argv[2];
size_t len = strlen(string);
if (len > buf_size) {
fprintf(stderr, "string is too long\en");
exit(exit_failure);
}
/* open the existing shared memory object and map it
into the caller\(aqs address space. */
int fd = shm_open(shmpath, o_rdwr, 0);
if (fd == \-1)
errexit("shm_open");
struct shmbuf *shmp = mmap(null, sizeof(*shmp),
prot_read | prot_write,
map_shared, fd, 0);
if (shmp == map_failed)
errexit("mmap");
/* copy data into the shared memory object. */