return tdb_nest_unlock(tdb, TRANSACTION_LOCK, ltype, false);
}
-
-/* lock/unlock entire database. It can only be upgradable if you have some
- * other way of guaranteeing exclusivity (ie. transaction write lock). */
-int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
- enum tdb_lock_flags flags, bool upgradable)
+/* Returns 0 if all done, -1 if error, 1 if ok. */
+static int tdb_allrecord_check(struct tdb_context *tdb, int ltype,
+ enum tdb_lock_flags flags, bool upgradable)
{
/* There are no locks on read-only dbs */
if (tdb->read_only || tdb->traverse_read) {
tdb->ecode = TDB_ERR_LOCK;
return -1;
}
+ return 1;
+}
+
+/* lock/unlock entire database. It can only be upgradable if you have some
+ * other way of guaranteeing exclusivity (ie. transaction write lock). */
+int tdb_allrecord_lock(struct tdb_context *tdb, int ltype,
+ enum tdb_lock_flags flags, bool upgradable)
+{
+ switch (tdb_allrecord_check(tdb, ltype, flags, upgradable)) {
+ case -1:
+ return -1;
+ case 0:
+ return 0;
+ }
if (tdb_brlock(tdb, ltype, FREELIST_TOP, 0, flags)) {
if (flags & TDB_LOCK_WAIT) {
return tdb_allrecord_unlock(tdb, F_RDLCK, false);
}
+/* We only need to lock individual bytes, but Linux merges consecutive locks
+ * so we lock in contiguous ranges. */
+static int tdb_chainlock_gradual(struct tdb_context *tdb,
+ size_t off, size_t len)
+{
+ int ret;
+
+ if (len <= 4) {
+ /* Single record. Just do blocking lock. */
+ return tdb_brlock(tdb, F_WRLCK, off, len, TDB_LOCK_WAIT);
+ }
+
+ /* First we try non-blocking. */
+ ret = tdb_brlock(tdb, F_WRLCK, off, len, TDB_LOCK_NOWAIT);
+ if (ret == 0) {
+ return 0;
+ }
+
+ /* Try locking first half, then second. */
+ ret = tdb_chainlock_gradual(tdb, off, len / 2);
+ if (ret == -1)
+ return -1;
+
+ ret = tdb_chainlock_gradual(tdb, off + len / 2, len - len / 2);
+ if (ret == -1) {
+ tdb_brunlock(tdb, F_WRLCK, off, len / 2);
+ return -1;
+ }
+ return 0;
+}
+
+/* We do the locking gradually to avoid being starved by smaller locks. */
+int tdb_lockall_gradual(struct tdb_context *tdb)
+{
+ int ret;
+
+ /* This checks for other locks, nesting. */
+ ret = tdb_allrecord_check(tdb, F_WRLCK, TDB_LOCK_WAIT, false);
+ if (ret == -1 || ret == 0)
+ return ret;
+
+ /* We cover two kinds of locks:
+ * 1) Normal chain locks. Taken for almost all operations.
+ * 3) Individual records locks. Taken after normal or free
+ * chain locks.
+ *
+ * It is (1) which cause the starvation problem, so we're only
+ * gradual for that. */
+ if (tdb_chainlock_gradual(tdb, FREELIST_TOP,
+ tdb->header.hash_size * 4) == -1) {
+ return -1;
+ }
+
+ /* Grab individual record locks. */
+ if (tdb_brlock(tdb, F_WRLCK, lock_offset(tdb->header.hash_size), 0,
+ TDB_LOCK_WAIT) == -1) {
+ tdb_brunlock(tdb, F_WRLCK, FREELIST_TOP,
+ tdb->header.hash_size * 4);
+ return -1;
+ }
+
+ /* That adds up to an allrecord lock. */
+ tdb->allrecord_lock.count = 1;
+ tdb->allrecord_lock.ltype = F_WRLCK;
+ tdb->allrecord_lock.off = false;
+
+ /* Just check we don't need recovery... */
+ if (tdb_needs_recovery(tdb)) {
+ tdb_allrecord_unlock(tdb, F_WRLCK, false);
+ if (tdb_lock_and_recover(tdb) == -1) {
+ return -1;
+ }
+ /* Try again. */
+ return tdb_lockall_gradual(tdb);
+ }
+
+ return 0;
+}
+
/* lock/unlock one hash chain. This is meant to be used to reduce
contention - it cannot guarantee how many records will be locked */
int tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)
int tdb_unlockall_read(struct tdb_context *tdb);
int tdb_lockall_mark(struct tdb_context *tdb);
int tdb_lockall_unmark(struct tdb_context *tdb);
+int tdb_lockall_gradual(struct tdb_context *tdb);
const char *tdb_name(struct tdb_context *tdb);
int tdb_fd(struct tdb_context *tdb);
tdb_log_func tdb_log_fn(struct tdb_context *tdb);
CFLAGS:=-I../../.. -Wall -O3 #-g -pg
LDFLAGS:=-L../../..
-default: replay_trace tdbtorture tdbdump tdbtool
+default: replay_trace tdbtorture tdbdump tdbtool starvation
benchmark: replay_trace
@trap "rm -f /tmp/trace.$$$$" 0; for f in benchmarks/*.rz; do if runzip -k $$f -o /tmp/trace.$$$$ && echo -n "$$f": && ./replay_trace --quiet -n 5 replay.tdb /tmp/trace.$$$$ && rm /tmp/trace.$$$$; then rm -f /tmp/trace.$$$$; else exit 1; fi; done
--- /dev/null
+/* Demonstrate starvation of tdb_lockall */
+#include <ccan/tdb/tdb.h>
+#include <err.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <time.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/time.h>
+
+static void usage(const char *extra)
+{
+ errx(1, "%s%s"
+ "Usage: starvation [lockall|gradual] <num> <worktime-in-ms>\n"
+ " Each locker holds lock for between 1/2 and 1 1/2 times\n"
+ " worktime, then sleeps for one second.\n\n"
+ " Main process tries tdb_lockall or tdb_lockall_gradual.",
+ extra ? extra : "", extra ? "\n" : "");
+}
+
+static void run_and_sleep(struct tdb_context *tdb, int parentfd, unsigned time)
+{
+ char c;
+ struct timespec hold;
+ unsigned rand, randtime;
+ TDB_DATA key;
+
+ key.dptr = (void *)&rand;
+ key.dsize = sizeof(rand);
+
+ while (read(parentfd, &c, 1) != 0) {
+ /* Lock a random key. */
+ rand = random();
+ if (tdb_chainlock(tdb, key) != 0)
+ errx(1, "chainlock failed: %s", tdb_errorstr(tdb));
+
+ /* Hold it for some variable time. */
+ randtime = time / 2 + (random() % time);
+ hold.tv_sec = randtime / 1000;
+ hold.tv_nsec = (randtime % 1000) * 1000000;
+ nanosleep(&hold, NULL);
+
+ if (tdb_chainunlock(tdb, key) != 0)
+ errx(1, "chainunlock failed: %s", tdb_errorstr(tdb));
+
+ /* Wait for a second without the lock. */
+ sleep(1);
+ }
+ exit(0);
+}
+
+static void logfn(struct tdb_context *tdb,
+ enum tdb_debug_level level,
+ const char *fmt, ...)
+{
+ va_list ap;
+
+ va_start(ap, fmt);
+ vfprintf(stderr, fmt, ap);
+ va_end(ap);
+}
+
+int main(int argc, char *argv[])
+{
+ int (*lockall)(struct tdb_context *);
+ unsigned int num, worktime, i;
+ int pfd[2];
+ struct tdb_context *tdb;
+ struct tdb_logging_context log = { logfn, NULL };
+ struct timeval start, end, duration;
+
+ if (argc != 4)
+ usage(NULL);
+
+ if (strcmp(argv[1], "lockall") == 0)
+ lockall = tdb_lockall;
+ else if (strcmp(argv[1], "gradual") == 0)
+ lockall = tdb_lockall_gradual;
+ else
+ usage("Arg1 should be 'lockall' or 'gradual'");
+
+ num = atoi(argv[2]);
+ worktime = atoi(argv[3]);
+
+ if (!num || !worktime)
+ usage("Number of threads and worktime must be non-zero");
+
+ if (pipe(pfd) != 0)
+ err(1, "Creating pipe");
+
+ tdb = tdb_open_ex("/tmp/starvation.tdb", 10000, TDB_DEFAULT,
+ O_RDWR|O_CREAT|O_TRUNC, 0600, &log, NULL);
+ if (!tdb)
+ err(1, "Opening tdb /tmp/starvation.tdb");
+
+ for (i = 0; i < num; i++) {
+ switch (fork()) {
+ case 0:
+ close(pfd[1]);
+ fcntl(pfd[0], F_SETFL,
+ fcntl(pfd[0], F_GETFL)|O_NONBLOCK);
+ srandom(getpid() + i);
+ if (tdb_reopen(tdb) != 0)
+ err(1, "Reopening tdb %s", tdb_name(tdb));
+
+ run_and_sleep(tdb, pfd[0], worktime);
+ case -1:
+ err(1, "forking");
+ }
+ /* Stagger the children. */
+ usleep(random() % (1000000 / num));
+ }
+
+ close(pfd[0]);
+ sleep(1);
+ gettimeofday(&start, NULL);
+ if (lockall(tdb) != 0)
+ errx(1, "lockall failed: %s", tdb_errorstr(tdb));
+ gettimeofday(&end, NULL);
+
+ duration.tv_sec = end.tv_sec - start.tv_sec;
+ duration.tv_usec = end.tv_usec - start.tv_usec;
+ if (duration.tv_usec < 0) {
+ --duration.tv_sec;
+ duration.tv_usec += 1000000;
+ }
+
+ if (tdb_unlockall(tdb) != 0)
+ errx(1, "unlockall failed: %s", tdb_errorstr(tdb));
+ tdb_close(tdb);
+ unlink("/tmp/starvation.tdb");
+
+ printf("Took %lu.%06lu seconds\n", duration.tv_sec, duration.tv_usec);
+ return 0;
+}