Allow timed waits with relative timeouts on locks and condvars.

Even though pthreads doesn't support this, there are various alternative
APIs that use this. For example, uv_cond_timedwait() accepts a relative
timeout. So does Rust's std::sync::Condvar::wait_timeout().

Though I personally think that relative timeouts are bad (due to
imprecision for repeated operations), it does seem that people want
this. Extend the existing futex functions to keep track of whether an
absolute timeout is used in a boolean flag.

MFC after:	1 month

2 files changed, 26 insertions, 23 deletions

diff --git a/sys/compat/cloudabi/cloudabi_futex.c b/sys/compat/cloudabi/cloudabi_futex.c
index d12b331f1872..153e8bce8495 100644
--- a/sys/compat/cloudabi/cloudabi_futex.c
+++ b/sys/compat/cloudabi/cloudabi_futex.c
@@ -197,7 +197,7 @@ static void futex_queue_requeue(struct futex_queue *, struct futex_queue *,
     unsigned int);
 static int futex_queue_sleep(struct futex_queue *, struct futex_lock *,
     struct futex_waiter *, struct thread *, cloudabi_clockid_t,
-    cloudabi_timestamp_t, cloudabi_timestamp_t);
+    cloudabi_timestamp_t, cloudabi_timestamp_t, bool);
 static cloudabi_tid_t futex_queue_tid_best(const struct futex_queue *);
 static void futex_queue_wake_up_all(struct futex_queue *);
 static void futex_queue_wake_up_best(struct futex_queue *);
@@ -427,7 +427,7 @@ futex_lock_lookup_locked(struct futex_address *fa)
 static int
 futex_lock_rdlock(struct futex_lock *fl, struct thread *td,
     cloudabi_lock_t *lock, cloudabi_clockid_t clock_id,
-    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision)
+    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision, bool abstime)
 {
 	struct futex_waiter fw;
 	int error;
@@ -438,7 +438,7 @@ futex_lock_rdlock(struct futex_lock *fl, struct thread *td,
 		KASSERT(fl->fl_owner != LOCK_UNMANAGED,
 		    ("Attempted to sleep on an unmanaged lock"));
 		error = futex_queue_sleep(&fl->fl_readers, fl, &fw, td,
-		    clock_id, timeout, precision);
+		    clock_id, timeout, precision, abstime);
 		KASSERT((error == 0) == fw.fw_locked,
 		    ("Should have locked write lock on success"));
 		KASSERT(futex_queue_count(&fw.fw_donated) == 0,
@@ -707,7 +707,7 @@ futex_lock_wake_up_next(struct futex_lock *fl, cloudabi_lock_t *lock)
 static int
 futex_lock_wrlock(struct futex_lock *fl, struct thread *td,
     cloudabi_lock_t *lock, cloudabi_clockid_t clock_id,
-    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision,
+    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision, bool abstime,
     struct futex_queue *donated)
 {
 	struct futex_waiter fw;
@@ -735,7 +735,7 @@ futex_lock_wrlock(struct futex_lock *fl, struct thread *td,
 		KASSERT(fl->fl_owner != LOCK_UNMANAGED,
 		    ("Attempted to sleep on an unmanaged lock"));
 		error = futex_queue_sleep(&fl->fl_writers, fl, &fw, td,
-		    clock_id, timeout, precision);
+		    clock_id, timeout, precision, abstime);
 		KASSERT((error == 0) == fw.fw_locked,
 		    ("Should have locked write lock on success"));
 		KASSERT(futex_queue_count(&fw.fw_donated) == 0,
@@ -789,16 +789,18 @@ futex_queue_convert_timestamp_relative(cloudabi_timestamp_t ts)
 static int
 futex_queue_convert_timestamp(struct thread *td, cloudabi_clockid_t clock_id,
     cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision,
-    sbintime_t *sbttimeout, sbintime_t *sbtprecision)
+    sbintime_t *sbttimeout, sbintime_t *sbtprecision, bool abstime)
 {
 	cloudabi_timestamp_t now;
 	int error;
 
-	/* Make the time relative. */
-	error = cloudabi_clock_time_get(td, clock_id, &now);
-	if (error != 0)
-		return (error);
-	timeout = timeout < now ? 0 : timeout - now;
+	if (abstime) {
+		/* Make the time relative. */
+		error = cloudabi_clock_time_get(td, clock_id, &now);
+		if (error != 0)
+			return (error);
+		timeout = timeout < now ? 0 : timeout - now;
+	}
 
 	*sbttimeout = futex_queue_convert_timestamp_relative(timeout);
 	*sbtprecision = futex_queue_convert_timestamp_relative(precision);
@@ -808,7 +810,7 @@ futex_queue_convert_timestamp(struct thread *td, cloudabi_clockid_t clock_id,
 static int
 futex_queue_sleep(struct futex_queue *fq, struct futex_lock *fl,
     struct futex_waiter *fw, struct thread *td, cloudabi_clockid_t clock_id,
-    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision)
+    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision, bool abstime)
 {
 	sbintime_t sbttimeout, sbtprecision;
 	int error;
@@ -821,7 +823,7 @@ futex_queue_sleep(struct futex_queue *fq, struct futex_lock *fl,
 	if (timeout != UINT64_MAX) {
 		/* Convert timeout duration. */
 		error = futex_queue_convert_timestamp(td, clock_id, timeout,
-		    precision, &sbttimeout, &sbtprecision);
+		    precision, &sbttimeout, &sbtprecision, abstime);
 		if (error != 0)
 			return (error);
 	}
@@ -976,7 +978,7 @@ int
 cloudabi_futex_condvar_wait(struct thread *td, cloudabi_condvar_t *condvar,
     cloudabi_scope_t condvar_scope, cloudabi_lock_t *lock,
     cloudabi_scope_t lock_scope, cloudabi_clockid_t clock_id,
-    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision)
+    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision, bool abstime)
 {
 	struct futex_condvar *fc;
 	struct futex_lock *fl;
@@ -1012,7 +1014,7 @@ cloudabi_futex_condvar_wait(struct thread *td, cloudabi_condvar_t *condvar,
 	/* Go to sleep. */
 	++fc->fc_waitcount;
 	error = futex_queue_sleep(&fc->fc_waiters, fc->fc_lock, &fw, td,
-	    clock_id, timeout, precision);
+	    clock_id, timeout, precision, abstime);
 	if (fw.fw_locked) {
 		/* Waited and got the lock assigned to us. */
 		KASSERT(futex_queue_count(&fw.fw_donated) == 0,
@@ -1031,7 +1033,8 @@ cloudabi_futex_condvar_wait(struct thread *td, cloudabi_condvar_t *condvar,
 		 *    responsible for reacquiring the userspace lock.
 		 */
 		error2 = futex_lock_wrlock(fl, td, lock,
-		    CLOUDABI_CLOCK_MONOTONIC, UINT64_MAX, 0, &fw.fw_donated);
+		    CLOUDABI_CLOCK_MONOTONIC, UINT64_MAX, 0, abstime,
+		    &fw.fw_donated);
 		if (error2 != 0)
 			error = error2;
 	} else {
@@ -1048,7 +1051,7 @@ cloudabi_futex_condvar_wait(struct thread *td, cloudabi_condvar_t *condvar,
 int
 cloudabi_futex_lock_rdlock(struct thread *td, cloudabi_lock_t *lock,
     cloudabi_scope_t scope, cloudabi_clockid_t clock_id,
-    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision)
+    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision, bool abstime)
 {
 	struct futex_lock *fl;
 	int error;
@@ -1059,7 +1062,7 @@ cloudabi_futex_lock_rdlock(struct thread *td, cloudabi_lock_t *lock,
 		return (error);
 
 	error = futex_lock_rdlock(fl, td, lock, clock_id, timeout,
-	    precision);
+	    precision, abstime);
 	futex_lock_release(fl);
 	return (error);
 }
@@ -1067,7 +1070,7 @@ cloudabi_futex_lock_rdlock(struct thread *td, cloudabi_lock_t *lock,
 int
 cloudabi_futex_lock_wrlock(struct thread *td, cloudabi_lock_t *lock,
     cloudabi_scope_t scope, cloudabi_clockid_t clock_id,
-    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision)
+    cloudabi_timestamp_t timeout, cloudabi_timestamp_t precision, bool abstime)
 {
 	struct futex_lock *fl;
 	struct futex_queue fq;
@@ -1080,7 +1083,7 @@ cloudabi_futex_lock_wrlock(struct thread *td, cloudabi_lock_t *lock,
 
 	futex_queue_init(&fq);
 	error = futex_lock_wrlock(fl, td, lock, clock_id, timeout,
-	    precision, &fq);
+	    precision, abstime, &fq);
 	futex_lock_release(fl);
 	return (error);
 }
diff --git a/sys/compat/cloudabi/cloudabi_util.h b/sys/compat/cloudabi/cloudabi_util.h
index d9a6096c73f1..0f07dc53fa29 100644
--- a/sys/compat/cloudabi/cloudabi_util.h
+++ b/sys/compat/cloudabi/cloudabi_util.h
@@ -65,13 +65,13 @@ int cloudabi_convert_timespec(const struct timespec *, cloudabi_timestamp_t *);
  */
 int cloudabi_futex_condvar_wait(struct thread *, cloudabi_condvar_t *,
     cloudabi_scope_t, cloudabi_lock_t *, cloudabi_scope_t, cloudabi_clockid_t,
-    cloudabi_timestamp_t, cloudabi_timestamp_t);
+    cloudabi_timestamp_t, cloudabi_timestamp_t, bool);
 int cloudabi_futex_lock_rdlock(struct thread *, cloudabi_lock_t *,
     cloudabi_scope_t, cloudabi_clockid_t, cloudabi_timestamp_t,
-    cloudabi_timestamp_t);
+    cloudabi_timestamp_t, bool);
 int cloudabi_futex_lock_wrlock(struct thread *, cloudabi_lock_t *,
     cloudabi_scope_t, cloudabi_clockid_t, cloudabi_timestamp_t,
-    cloudabi_timestamp_t);
+    cloudabi_timestamp_t, bool);
 
 /* Socket operations. */
 int cloudabi_sock_recv(struct thread *, cloudabi_fd_t, struct iovec *, size_t,