Attached another test program. I don't expect it to print any errors with any OS, but I'd like to confirm it for non-Linux SMP kernels.
(Except for OpenBSD, it doesn't work correctly in it anyway because it doesn't support mixing write()s and mmap())
/*
gcc concurrency.c -o concurrency -Wall
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/mman.h>
#define MAX_PAGESIZE (8192)
int main(int argc, char *argv[])
{
char buf[MAX_PAGESIZE*2], ones[4] = { 1, 1, 1, 1 };
int fd, pagesize;
int process_count = 5;
void *mmap_base = NULL;
size_t mmap_size = 0;
struct stat st;
int fixed;
memset(buf, 0, sizeof(buf));
pagesize = getpagesize();
assert(pagesize <= MAX_PAGESIZE);
buf[pagesize] = 'h';
if (fork() == 0) {
printf("writing, page size = %d\n", pagesize);
for (;;) {
fd = open("foo2", O_RDWR | O_CREAT | O_TRUNC, 0600);
if (fd == -1) {
perror("open()");
return 1;
}
if (flock(fd, LOCK_EX) < 0)
perror("flock()");
if (rename("foo2", "foo") < 0)
perror("rename()");
usleep(rand() % 1000);
pwrite(fd, buf, pagesize + 16, 0);
//usleep(rand() % 1000);
//fdatasync(fd);
pwrite(fd, ones, 4, pagesize-4);
if (flock(fd, LOCK_UN) < 0)
perror("flock()");
close(fd);
usleep(rand() % 1000);
}
} else {
while (process_count-- > 1) {
if (fork() == 0)
break;
}
printf("%d: reading, page size = %d\n", process_count, pagesize);
for (;; close(fd), usleep(rand() % 1000)) {
fd = open("foo", O_RDWR, 0600);
if (fd == -1) {
perror("open()");
return 1;
}
if (fstat(fd, &st) < 0)
perror("fstat()");
fixed = 0;
again:
if (st.st_size < pagesize)
continue;
if (mmap_base != NULL && mmap_base != MAP_FAILED)
munmap(mmap_base, mmap_size);
mmap_size = st.st_size;
mmap_base = mmap(NULL, mmap_size, PROT_READ,
MAP_SHARED, fd, 0);
if (memcmp((char *)mmap_base + pagesize - 4,
ones, 4) == 0) {
if (mmap_size != pagesize+16) {
if (mmap_size == pagesize &&
fstat(fd, &st) == 0 &&
st.st_size != pagesize) {
fixed = 1;
goto again;
}
printf("page size cut, mmap_size=%ld\n", mmap_size);
} else if (((char *)mmap_base)[pagesize] != 'h')
printf("broken data\n");
}
}
}
return 0;
}
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