I want to share data between two (ndk-) processes. For this I use ashmem using this one. One process reads continuously ( read_mem), and one process writes once ( write_mem).
The problem is that the read process does not get the value of the record.
AND
Watching the reader’s cards, I found that android deletes the shared memory file immediately after ashmem_create_region.
read_mem.c
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
#include "ashmem.h"
#define SHM_NAME "test_mem"
int main(int argc, char **argv) {
int shID = ashmem_create_region(SHM_NAME, 2);
if (shID < 0)
{
perror("ashmem_create_region failed\n");
return 1;
}
printf("ashmem_create_region: %d\n", shID);
char *sh_buffer = (char*)mmap(NULL, 2, PROT_READ | PROT_WRITE, MAP_SHARED, shID, 0);
if (sh_buffer == (char*)-1)
{
perror("mmap failed");
return 1;
}
printf("PID=%d", getpid());
do
{
printf("VALUE = 0x%x\n", sh_buffer[0]);
}
while (getchar());
return 0;
}
write_mem.c
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
#include "ashmem.h"
#define SHM_NAME "test_mem"
int main(int argc, char **argv) {
int shID = ashmem_create_region(SHM_NAME, 2);
if (shID < 0)
{
perror("ashmem_create_region failed\n");
return 1;
}
printf("ashmem_create_region: %d\n", shID);
char *sh_buffer = (char*)mmap(NULL, 2, PROT_READ | PROT_WRITE, MAP_SHARED, shID, 0);
if (sh_buffer == (char*)-1)
{
perror("mmap failed");
return 1;
}
printf("PID=%d\n", getpid());
int ch = getchar();
sh_buffer[0] = ch;
printf("Written 0x%x\n", ch);
munmap(sh_buffer, 2);
close(shID);
return 0;
}
This is the result:
Reading
130|shell@mako:/data/local/tmp $ ./read_mem
ashmem_create_region: 3
PID=29655
VALUE = 0x0
Record
shell@mako:/data/local/tmp $ ./write_mem
ashmem_create_region: 3
PID=29691
A
Written 0x41
Repeat reading VALUE = 0x0(by pressing the return button)
View reader cards:
shell@mako:/ $ cat /proc/29655/maps | grep test_mem
b6ef5000-b6ef6000 rw-s 00000000 00:04 116213 /dev/ashmem/test_mem (deleted)
as you can see test_memdeleted WHILE read_mem still alive.
Other information
android ndk-build
: LG Nexus 4 (AOSP Lollypop)
/dev/ashmem, .
ashmem,