From 4a69b8adb9bef2a5c7f7bec061d0bdda95ad9e24 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 4 Apr 2024 15:34:37 +0900
Subject: [PATCH v4] Add "ABI_compatibility" regions in wait_event_names.txt

When backpatching, adding an event will renumber others, which can make an
extension report the wrong event until recompiled. This is due to the fact that
generate-wait_event_types.pl sorts events to position them. The "ABI_compatibility"
region added here ensures no ordering is done for the wait events found after
this delimiter.
---
 .../activity/generate-wait_event_types.pl     | 27 ++++++++++++++++++-
 .../utils/activity/wait_event_names.txt       | 17 ++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)
 100.0% src/backend/utils/activity/

diff --git a/src/backend/utils/activity/generate-wait_event_types.pl b/src/backend/utils/activity/generate-wait_event_types.pl
index f1adf0e8e7..9768406db5 100644
--- a/src/backend/utils/activity/generate-wait_event_types.pl
+++ b/src/backend/utils/activity/generate-wait_event_types.pl
@@ -38,7 +38,9 @@ die "Not possible to specify --docs and --code simultaneously"
 
 open my $wait_event_names, '<', $ARGV[0] or die;
 
+my @abi_compatibility_lines;
 my @lines;
+my $abi_compatibility = 0;
 my $section_name;
 my $note;
 my $note_name;
@@ -59,10 +61,27 @@ while (<$wait_event_names>)
 	{
 		$section_name = $_;
 		$section_name =~ s/^.*- //;
+		$abi_compatibility = 0;
 		next;
 	}
 
-	push(@lines, $section_name . "\t" . $_);
+	# ABI_compatibility region, preserving ABI compatibility of the code
+	# generated.  Any wait events listed in this part of the file
+	# will not be sorted during the code generation.
+	if (/^ABI_compatibility:$/)
+	{
+		$abi_compatibility = 1;
+		next;
+	}
+
+	if ($gen_code && $abi_compatibility)
+	{
+		push(@abi_compatibility_lines, $section_name . "\t" . $_);
+	}
+	else
+	{
+		push(@lines, $section_name . "\t" . $_);
+	}
 }
 
 # Sort the lines based on the second column.
@@ -70,6 +89,12 @@ while (<$wait_event_names>)
 my @lines_sorted =
   sort { uc((split(/\t/, $a))[1]) cmp uc((split(/\t/, $b))[1]) } @lines;
 
+# If we are generating code, concat @lines_sorted and then @abi_compatibility_lines.
+if ($gen_code)
+{
+	push(@lines_sorted, @abi_compatibility_lines);
+}
+
 # Read the sorted lines and populate the hash table
 foreach my $line (@lines_sorted)
 {
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index 0d288d6b3d..fbb5dae5ea 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -26,6 +26,12 @@
 # When adding a new wait event, make sure it is placed in the appropriate
 # ClassName section.
 #
+# Wait events added in stable branches should be appended to the lists in
+# the "ABI_compatibility:" region of their related ClassName section to preserve
+# ABI compatibility of the C code generated from this file's data, respecting
+# the order of any wait event already listed there.  The "ABI_compatibility:"
+# regions should remain empty on the master branch and on unreleased branches.
+#
 # WaitEventLWLock and WaitEventLock have their own C code for their wait event
 # enums and function names.  Hence, for these, only the SGML documentation is
 # generated.
@@ -61,6 +67,7 @@ WAL_SENDER_MAIN	"Waiting in main loop of WAL sender process."
 WAL_SUMMARIZER_WAL	"Waiting in WAL summarizer for more WAL to be generated."
 WAL_WRITER_MAIN	"Waiting in main loop of WAL writer process."
 
+ABI_compatibility:
 
 #
 # Wait Events - Client
@@ -83,6 +90,7 @@ WAIT_FOR_WAL_REPLAY	"Waiting for a replay of the particular WAL position on the
 WAL_SENDER_WAIT_FOR_WAL	"Waiting for WAL to be flushed in WAL sender process."
 WAL_SENDER_WRITE_DATA	"Waiting for any activity when processing replies from WAL receiver in WAL sender process."
 
+ABI_compatibility:
 
 #
 # Wait Events - IPC
@@ -150,6 +158,7 @@ WAL_RECEIVER_WAIT_START	"Waiting for startup process to send initial data for st
 WAL_SUMMARY_READY	"Waiting for a new WAL summary to be generated."
 XACT_GROUP_UPDATE	"Waiting for the group leader to update transaction status at end of a parallel operation."
 
+ABI_compatibility:
 
 #
 # Wait Events - Timeout
@@ -170,6 +179,7 @@ VACUUM_DELAY	"Waiting in a cost-based vacuum delay point."
 VACUUM_TRUNCATE	"Waiting to acquire an exclusive lock to truncate off any empty pages at the end of a table vacuumed."
 WAL_SUMMARIZER_ERROR	"Waiting after a WAL summarizer error."
 
+ABI_compatibility:
 
 #
 # Wait Events - IO
@@ -257,6 +267,7 @@ WAL_SYNC	"Waiting for a WAL file to reach durable storage."
 WAL_SYNC_METHOD_ASSIGN	"Waiting for data to reach durable storage while assigning a new WAL sync method."
 WAL_WRITE	"Waiting for a write to a WAL file."
 
+ABI_compatibility:
 
 #
 # Wait Events - Buffer Pin
@@ -266,6 +277,7 @@ Section: ClassName - WaitEventBufferPin
 
 BUFFER_PIN	"Waiting to acquire an exclusive pin on a buffer."
 
+ABI_compatibility:
 
 #
 # Wait Events - Extension
@@ -275,6 +287,8 @@ Section: ClassName - WaitEventExtension
 
 Extension	"Waiting in an extension."
 
+ABI_compatibility:
+
 #
 # Wait Events - LWLock
 #
@@ -379,6 +393,7 @@ SubtransSLRU	"Waiting to access the sub-transaction SLRU cache."
 XactSLRU	"Waiting to access the transaction status SLRU cache."
 ParallelVacuumDSA	"Waiting for parallel vacuum dynamic shared memory allocation."
 
+# No "ABI_compatibility" region here as has its own C code.
 
 #
 # Wait Events - Lock
@@ -401,3 +416,5 @@ object	"Waiting to acquire a lock on a non-relation database object."
 userlock	"Waiting to acquire a user lock."
 advisory	"Waiting to acquire an advisory user lock."
 applytransaction	"Waiting to acquire a lock on a remote transaction being applied by a logical replication subscriber."
+
+# No "ABI_compatibility" region here as has its own C code.
-- 
2.34.1

