File 2971-erts-Use-multi-time-warp-mode-by-default.patch of Package erlang
From c0f293afcecca2007805ecd02fe9017052425428 Mon Sep 17 00:00:00 2001
From: Rickard Green <rickard@erlang.org>
Date: Fri, 3 Jun 2022 14:10:38 +0200
Subject: [PATCH] [erts] Use multi time warp mode by default
---
erts/doc/src/time_correction.xml | 60 +++++++++++--------
erts/emulator/beam/erl_init.c | 2 +-
.../upcoming_incompatibilities.xml | 13 ----
3 files changed, 36 insertions(+), 39 deletions(-)
diff --git a/erts/doc/src/time_correction.xml b/erts/doc/src/time_correction.xml
index b3a36b907e..17263c26fe 100644
--- a/erts/doc/src/time_correction.xml
+++ b/erts/doc/src/time_correction.xml
@@ -34,29 +34,42 @@
</header>
<section>
- <title>New Extended Time Functionality</title>
- <note><p>As from Erlang/OTP 18 (ERTS 7.0) the time functionality
- has been extended. This includes a
+ <title>Extended Time Functionality</title>
+
+ <p>As of Erlang/OTP 18 (ERTS 7.0) the time functionality
+ was extended. This includes a
<seeguide marker="#The_New_Time_API">new API</seeguide>
for time and
<seeguide marker="#Time_Warp_Modes">time warp
modes</seeguide> that change the system behavior when
system time changes.</p>
- <p>The <seeguide marker="#No_Time_Warp_Mode">default
- time warp mode</seeguide> has the same behavior as before, and the
- old API still works. Thus, you are not required to change
- anything unless you want to. However, <em>you are strongly
- encouraged to use the new API</em> instead of the old API based
- on <seemfa marker="erlang#now/0"><c>erlang:now/0</c></seemfa>.
- <c>erlang:now/0</c> is deprecated, as it is and
- will be a scalability bottleneck.</p>
-
- <p>By using the new API, you
- automatically get scalability and performance improvements. This
- also enables you to use the
- <seeguide marker="#Multi_Time_Warp_Mode">multi-time warp mode</seeguide>
- that improves accuracy and precision of time measurements.</p>
+ <note>
+ <p>
+ As of Erlang/OTP 26 (ERTS 14.0) the
+ <seeguide marker="#Multi_Time_Warp_Mode">multi time warp
+ mode</seeguide> is enabled by default. This assumes that all
+ code executing on the system is
+ <seeguide marker="#Time_Warp_Safe_Code">time warp safe</seeguide>.
+ </p>
+ <p>
+ If you have old code in the system that is not time warp
+ safe, you now explicitly need to start the system in
+ <seeguide marker="#No_Time_Warp_Mode">no time warp
+ mode</seeguide> (or
+ <seeguide marker="#Single_Time_Warp_Mode">singe time warp
+ mode</seeguide> if it is partially time warp safe) in order
+ to avoid problems. When starting the system in no time warp
+ mode, the system behaves as it did prior to the introduction
+ of the extended time functionality introduced in OTP 18.
+ </p>
+ <p>
+ If you have code that is not time warp safe, you are strongly
+ encouraged to change this so that you can use multi time
+ warp mode. Compared to no time warp mode, multi time warp
+ mode improves scalability and performance as well as accuracy
+ and precision of time measurements.
+ </p>
</note>
</section>
@@ -405,13 +418,9 @@
<section>
<title>No Time Warp Mode</title>
<p>The time offset is determined at runtime system start
- and does not change later. This is the default behavior, but
- not because it is the best mode (which it is not). It is
- default <em>only</em> because this is how the runtime system
- behaved until ERTS 7.0.
- Ensure that your Erlang code that can execute during a time
- warp is <seeguide marker="#Time_Warp_Safe_Code">time warp
- safe</seeguide> before enabling other modes.</p>
+ and does not change later. This is the same behavior as was
+ default prior to OTP 26 (ERTS 14.0), and the only behavior
+ prior to OTP 18 (ERTS 7.0).</p>
<p>As the time offset is not allowed to change, time
correction must adjust the frequency of the Erlang
@@ -558,7 +567,8 @@
better, and behave better on almost all platforms.
Also, the accuracy and precision of time measurements
are better. Only Erlang runtime systems executing on
- ancient platforms benefit from another configuration.</p>
+ ancient platforms benefit from another configuration.
+ As of OTP 26 (ERTS 14.0) this is also the default.</p>
<p>The time offset can change at any time without limitations.
That is, Erlang system time can perform time warps both
diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c
index 872fa6b613..62c11668ed 100644
--- a/erts/emulator/beam/erl_init.c
+++ b/erts/emulator/beam/erl_init.c
@@ -275,7 +275,7 @@ static ERTS_INLINE void
set_default_time_adj(int *time_correction_p, ErtsTimeWarpMode *time_warp_mode_p)
{
*time_correction_p = 1;
- *time_warp_mode_p = ERTS_NO_TIME_WARP_MODE;
+ *time_warp_mode_p = ERTS_MULTI_TIME_WARP_MODE;
if (!erts_check_time_adj_support(*time_correction_p,
*time_warp_mode_p)) {
*time_correction_p = 0;
diff --git a/system/doc/general_info/upcoming_incompatibilities.xml b/system/doc/general_info/upcoming_incompatibilities.xml
index 59003d2243..90774672bd 100644
--- a/system/doc/general_info/upcoming_incompatibilities.xml
+++ b/system/doc/general_info/upcoming_incompatibilities.xml
@@ -132,18 +132,5 @@
</list>
</section>
- <section>
- <title>The default timewarp mode will change to multi-time warp mode</title>
- <p>
- The default <seeguide marker="erts:time_correction#Time_Warp_Modes">
- Time Warp Mode</seeguide> will be changed from
- <seeguide marker="erts:time_correction#No_Time_Warp_Mode">
- no time warp mode</seeguide> to <seeguide marker="erts:time_correction#Multi_Time_Warp_Mode">
- multi-time warp mode</seeguide>. See <seeguide marker="erts:time_correction">
- Time and Time Correction in Erlang</seeguide> for details on how this will
- effect your system.
- </p>
- </section>
-
</section>
</chapter>
--
2.35.3
