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/* Simple code to grab a lock to restrict number of parallel processes. */
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "ccontrol.h"
#include "stdrusty.h"
/* We place much looser limits on "fast" operations: distcc-ables and make */
#define DISTCC_LIMIT 20
/* Make is limited separately for each depth, since it can recurse. */
#define MAKE_LIMIT 3
#define IPC_KEY 0xCCD1ED
static void fcntl_lock(int fd, bool lock, unsigned int offset)
{
struct flock fl;
fl.l_type = lock ? F_WRLCK : F_UNLCK;
fl.l_whence = SEEK_SET;
fl.l_start = offset;
fl.l_len = 1;
if (fcntl(fd, F_SETLKW, &fl) < 0)
fatal("cannot lock config file", errno, NULL);
}
/* To create an initialized semaphore, we need a lock. Use fcntl lock. */
static int make_semaphore(int fd, struct section sec, int key)
{
int id;
fcntl_lock(fd, true, 0);
id = semget(key, 1, IPC_CREAT|IPC_EXCL);
if (id < 0) {
int saved_errno = errno;
/* We might have raced, try again. */
id = semget(key, 1, 0);
errno = saved_errno;
} else {
union semun {
int val;
struct semid_ds *buf;
unsigned short *array;
struct seminfo *__buf;
} semctl_arg;
struct semid_ds ds;
verbose(sec.verbose, "Created slow lock");
memset(&ds, 0, sizeof(ds));
ds.sem_perm.uid = geteuid();
ds.sem_perm.gid = getegid();
ds.sem_perm.mode = 0600;
semctl_arg.buf = &ds;
if (semctl(id, 0, IPC_SET, semctl_arg) < 0)
fatal("cannot set semaphore permissions",
errno, NULL);
semctl_arg.val = sec.cpus;
if (semctl(id, 0, SETVAL, semctl_arg) < 0)
fatal("cannot set semaphore value", errno, NULL);
}
fcntl_lock(fd, false, 0);
return id;
}
/* Semaphores give us exact control over rate, but SEM_UNDO space is
* often limited (not on Linux tho AFAICT). */
static void grab_sem(int fd, struct section sec)
{
struct sembuf sop;
int id, key;
key = IPC_KEY + geteuid();
id = semget(key, 1, 0);
if (id < 0 && errno == ENOENT)
id = make_semaphore(fd, sec, key);
if (id < 0)
fatal("cannot get semaphore", errno, NULL);
again:
sop.sem_num = 0;
sop.sem_op = -1;
sop.sem_flg = SEM_UNDO;
if (semop(id, &sop, 1) != 0) {
if (errno == EINTR)
goto again;
fatal("cannot decrement semaphore", errno, NULL);
}
}
/* Since we have lots of these, we use fcntl locks as an approximate
* means to limit them. */
static void grab_fcntl_lock(int fd, unsigned int base, unsigned int max)
{
srand(getpid());
fcntl_lock(fd, true, base + rand()%max);
}
static void set_lock_envvar(char depth)
{
char locktype[2];
locktype[0] = depth;
locktype[1] = '\0';
setenv("CCONTROL_LOCK", locktype, 1);
}
static void undo_decrement_envvar(void)
{
char *depth = getenv("CCONTROL_LOCK");
set_lock_envvar(depth[0] - 1);
}
void drop_slow_lock(void)
{
struct sembuf sop;
int id, key;
assert(getenv("CCONTROL_LOCK"));
assert(getenv("CCONTROL_LOCK")[0] == '0');
key = IPC_KEY + geteuid();
id = semget(key, 1, 0);
if (id < 0)
fatal("cannot re-get semaphore", errno, NULL);
sop.sem_num = 0;
sop.sem_op = 1;
sop.sem_flg = SEM_UNDO;
if (semop(id, &sop, 1) != 0)
fatal("cannot increment semaphore", errno, NULL);
unsetenv("CCONTROL_LOCK");
}
static void undo_unset_envvar(void)
{
unsetenv("CCONTROL_LOCK");
}
static void undo_nothing(void)
{
}
undofn_t grab_lock(int fd, struct section sec, enum type type)
{
char *lock = getenv("CCONTROL_LOCK");
unsigned int distcc_lim, make_off, make_lim;
verbose(sec.verbose, "Grabbing lock for ",
type == TYPE_CC ? "CC"
: type == TYPE_CPLUSPLUS ? "C++"
: type == TYPE_MAKE ? "MAKE"
: type == TYPE_LD ? "LD" : "UNKNOWN");
/* If we already have slow lock, don't grab again (gcc calls ld). */
if (lock && lock[0] == '0') {
verbose(sec.verbose, "Already got it");
return undo_nothing;
}
/* Position 0 is used to initialize slow semaphore.
* Next range is used by distcc-able builds.
* Then a series of ranges for each makefile depth. */
make_off = distcc_lim = sec.cpus*DISTCC_LIMIT;
make_lim = sec.cpus*MAKE_LIMIT;
/* Make can run in parallel. */
if (type == TYPE_MAKE) {
unsigned int depth = 0;
/* Each level of make limited separately (tends to recurse) */
if (lock)
depth = lock[0] - 'A' + 1;
verbose(sec.verbose, "Getting fast lock for make");
/* No locks for top-level make. */
if (lock)
grab_fcntl_lock(fd, 1 + make_off + depth * make_lim,
make_lim);
set_lock_envvar('A' + depth);
return undo_decrement_envvar;
} else if (!sec.distcc) {
verbose(sec.verbose, "Getting slow lock for non-distcc");
/* LD or non-distcc compile. Single file! */
grab_sem(fd, sec);
set_lock_envvar('0');
return drop_slow_lock;
} else {
/* gcc & g++ are limited together. */
if (lock && lock[0] == '1')
fatal("called myself?", 0, NULL);
verbose(sec.verbose, "Getting fast lock for compile");
grab_fcntl_lock(fd, 1, distcc_lim);
set_lock_envvar('1');
return undo_unset_envvar;
}
}
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