From 3d4bed3374861d618622dfe2d5f8d37e8993c56c Mon Sep 17 00:00:00 2001
From: Christian Helmuth <christian.helmuth@genode-labs.com>
Date: Wed, 5 Feb 2020 10:59:32 +0100
Subject: [PATCH] libc: unify semantic of sleep functions

sleep(), usleep(), and nanosleep() now return immediately on
zero-timeout. Also, non-zero timeouts sleep at least 1 ms (the current
minimal timeout in libc), which compensates rounding errors.

Issue #3550
---
 repos/libports/src/lib/libc/sleep.cc | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/repos/libports/src/lib/libc/sleep.cc b/repos/libports/src/lib/libc/sleep.cc
index eac81a38a..e2e9ccacc 100644
--- a/repos/libports/src/lib/libc/sleep.cc
+++ b/repos/libports/src/lib/libc/sleep.cc
@@ -53,10 +53,15 @@ static void millisleep(Genode::uint64_t timeout_ms)
 extern "C" __attribute__((weak))
 int nanosleep(const struct timespec *req, struct timespec *rem)
 {
+	/* XXX nanosleep({0,0}) may yield but is not required to do so */
+	if (!req->tv_sec && !req->tv_nsec) return 0;
+
 	Genode::uint64_t sleep_ms = (Genode::uint64_t)req->tv_sec*1000;
 	if (req->tv_nsec)
 		sleep_ms += req->tv_nsec / 1000000;
-	millisleep(sleep_ms);
+
+	/* sleep at least 1 ms */
+	millisleep(sleep_ms ? : 1);
 
 	if (rem)
 		*rem = { 0, 0 };
@@ -101,8 +106,13 @@ int __sys_clock_nanosleep(clockid_t clock_id, int flags,
 extern "C" __attribute__((weak))
 unsigned int sleep(unsigned int seconds)
 {
-	Genode::uint64_t const sleep_ms = 1000 * (Genode::uint64_t)seconds;
-	millisleep(sleep_ms);
+	/* XXX sleep(0) may yield but is not required to do so */
+	if (!seconds) return 0;
+
+	Libc::uint64_t const sleep_ms = (Libc::uint64_t)seconds*1000;
+
+	/* sleep at least 1 ms */
+	millisleep(sleep_ms ? : 1);
 	return 0;
 }
 
@@ -110,8 +120,13 @@ unsigned int sleep(unsigned int seconds)
 extern "C" __attribute__((weak))
 int usleep(useconds_t useconds)
 {
-	if (useconds)
-		millisleep(useconds / 1000);
+	/* XXX usleep(0) may yield but is not required to do so */
+	if (!useconds) return 0;
+
+	Libc::uint64_t const sleep_ms = (Libc::uint64_t)useconds/1000;
+
+	/* sleep at least 1 ms */
+	millisleep(sleep_ms ? : 1);
 	return 0;
 }