void openSeekRead(char *filename, bits64 offset, bits64 len, char *buf)
/* Read len bits starting at offset from filename into buf or die. */
{
int fd = mustOpenFd(filename, O_RDONLY);
mustLseek(fd, offset, SEEK_SET);
mustReadFd(fd, buf, len);
mustCloseFd(&fd);
}
// TODO move this to a generic re-usable location
void startBackgroundWork(char *exec, char **pWorkUrl)
/* deal with forking off child for background work
* and setting up the trash file for communicating
* from the child to the browser */
{
char *workUrl = NULL;
char hgsid[64];
struct tempName tn;
safef(hgsid, sizeof(hgsid), "%s", cartSessionId(cart));
trashDirFile(&tn, "backGround", hgsid, ".tmp");
workUrl = cloneString(tn.forCgi);
fflush(stdout);
fflush(stderr);
// seems that we need to use the double-fork trick
// to create enough separation between the non-waiting parent
// and the grand-child process. otherwise the OS and Apache are waiting on the child.
int pid = fork();
if (pid == -1)
{
errAbort("can't fork, error %d", errno);
}
if (pid == 0) // child
{
int pid2 = fork();
if (pid2 == -1)
{
errAbort("can't fork, error %d", errno);
}
if (pid2 == 0) // grand child
{
// we need to close or redup to open stdout, stderr, stdin
// in order for apache to break ties with it.
// Will the grandchild cgi still be able to function?
// redirect stdout of child to the trash file for easier use of
// library functions that output html to stdout.
int out = mustOpenFd(tn.forCgi, O_WRONLY | O_CREAT);
fflush(stdout);
dup2(out,STDOUT_FILENO); /* closes STDOUT before setting it back to saved descriptor */
close(out);
// Unfortunately we must create our own stderr log file
char errName[1024];
safef(errName, sizeof errName, "%s.err", tn.forCgi);
int err = mustOpenFd(errName, O_CREAT | O_WRONLY | O_APPEND);
dup2(err, STDERR_FILENO);
close(err);
// stdin input is just empty
int in = mustOpenFd("/dev/null", O_RDONLY);
dup2(in, STDIN_FILENO);
close(in);
// execute so that we will be able to use database and other operations normally.
char execPath[4096];
safef(execPath, sizeof execPath, "%s hgsid=%s", exec, hgsid);
char *args[10];
int numArgs = chopString(execPath, " ", args, 10);
args[numArgs] = NULL;
// by creating a minimal environment and not inheriting from the parent,
// it cause cgiSpoof to run, picking up command-line params as cgi vars.
char *newenviron[] = { "HGDB_CONF=hg.conf", NULL };
int sleepSeconds = 1; // was 5
sleep(sleepSeconds); // Give the foreground process time to write the cart.
execve(args[0], args+1, newenviron);
// SHOULD NOT GET HERE UNLESS EXEC FAILED.
verbose(1,"execve failed for %s\n", exec);
_exit(0); // exit without the usual cleanup which messes up parent's db connections etc.
}
else // child
{
_exit(0); // exit without the usual cleanup which messes up parent's db connections etc.
}
}
else // parent
{
*pWorkUrl = workUrl;
// wait for the exiting child (not grandchild)
int w, status;
do {
w = waitpid(pid, &status, WUNTRACED | WCONTINUED);
if (w == -1)
{
perror("waitpid");
exit(EXIT_FAILURE);
}
if (WIFEXITED(status))
{
if (WEXITSTATUS(status) != 0)
verbose(1, "exited, status=%d\n", WEXITSTATUS(status));
}
else if (WIFSIGNALED(status))
{
verbose(1, "killed by signal %d\n", WTERMSIG(status));
}
else if (WIFSTOPPED(status))
{
verbose(1, "stopped by signal %d\n", WSTOPSIG(status));
}
else if (WIFCONTINUED(status))
{
verbose(1, "continued\n");
}
} while (!WIFEXITED(status) && !WIFSIGNALED(status));
// done waiting for child.
}
}