From d2c44cba771defa02c47d0c503c5c817163d0842 Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@scylladb.com>
Date: Mon, 5 Dec 2022 21:58:48 +0200
Subject: [PATCH 1/3] compaction_manager: make
 postponed_compactions_reevaluation() return a future

postponed_compactions_reevaluation() runs until compaction_manager is
stopped, checking if it needs to launch new compactions.

Make it return a future instead of stashing its completion somewhere.
This makes is easier to convert it to a coroutine.
---
 compaction/compaction_manager.cc | 6 +++---
 compaction/compaction_manager.hh | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/compaction/compaction_manager.cc b/compaction/compaction_manager.cc
index e614d2d634..15f11823ad 100644
--- a/compaction/compaction_manager.cc
+++ b/compaction/compaction_manager.cc
@@ -737,7 +737,7 @@ void compaction_manager::enable() {
     assert(_state == state::none || _state == state::disabled);
     _state = state::enabled;
     _compaction_submission_timer.arm(periodic_compaction_submission_interval());
-    postponed_compactions_reevaluation();
+    _waiting_reevalution = postponed_compactions_reevaluation();
 }
 
 std::function<void()> compaction_manager::compaction_submission_callback() {
@@ -748,8 +748,8 @@ std::function<void()> compaction_manager::compaction_submission_callback() {
     };
 }
 
-void compaction_manager::postponed_compactions_reevaluation() {
-    _waiting_reevalution = repeat([this] {
+future<> compaction_manager::postponed_compactions_reevaluation() {
+     return repeat([this] {
         return _postponed_reevaluation.wait().then([this] {
             if (_state != state::enabled) {
                 _postponed.clear();
diff --git a/compaction/compaction_manager.hh b/compaction/compaction_manager.hh
index 9ec90bec1a..ec5bee12da 100644
--- a/compaction/compaction_manager.hh
+++ b/compaction/compaction_manager.hh
@@ -350,7 +350,7 @@ private:
     // table still exists and compaction is not disabled for the table.
     inline bool can_proceed(compaction::table_state* t) const;
 
-    void postponed_compactions_reevaluation();
+    future<> postponed_compactions_reevaluation();
     void reevaluate_postponed_compactions() noexcept;
     // Postpone compaction for a table that couldn't be executed due to ongoing
     // similar-sized compaction.

From 1669025736fb647d4e840340ea44867cda6eb7dc Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@scylladb.com>
Date: Mon, 5 Dec 2022 22:01:41 +0200
Subject: [PATCH 2/3] compaction_manager: coroutinize
 postponed_compactions_reevaluation()

So much nicer.
---
 compaction/compaction_manager.cc | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/compaction/compaction_manager.cc b/compaction/compaction_manager.cc
index 15f11823ad..9c29a42ebe 100644
--- a/compaction/compaction_manager.cc
+++ b/compaction/compaction_manager.cc
@@ -749,11 +749,12 @@ std::function<void()> compaction_manager::compaction_submission_callback() {
 }
 
 future<> compaction_manager::postponed_compactions_reevaluation() {
-     return repeat([this] {
-        return _postponed_reevaluation.wait().then([this] {
+     while (true) {
+        co_await _postponed_reevaluation.when();
+        {
             if (_state != state::enabled) {
                 _postponed.clear();
-                return stop_iteration::yes;
+                co_return;
             }
             auto postponed = std::move(_postponed);
             try {
@@ -765,9 +766,8 @@ future<> compaction_manager::postponed_compactions_reevaluation() {
             } catch (...) {
                 _postponed = std::move(postponed);
             }
-            return stop_iteration::no;
-        });
-    });
+        }
+    }
 }
 
 void compaction_manager::reevaluate_postponed_compactions() noexcept {

From d2b1d2f69526d64da3c7688bfb7abfddeda09966 Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@scylladb.com>
Date: Mon, 5 Dec 2022 22:02:27 +0200
Subject: [PATCH 3/3] compaction_manager: reindent
 postponed_compactions_reevaluation()

---
 compaction/compaction_manager.cc | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/compaction/compaction_manager.cc b/compaction/compaction_manager.cc
index 9c29a42ebe..ea3900085e 100644
--- a/compaction/compaction_manager.cc
+++ b/compaction/compaction_manager.cc
@@ -751,21 +751,19 @@ std::function<void()> compaction_manager::compaction_submission_callback() {
 future<> compaction_manager::postponed_compactions_reevaluation() {
      while (true) {
         co_await _postponed_reevaluation.when();
-        {
-            if (_state != state::enabled) {
-                _postponed.clear();
-                co_return;
-            }
-            auto postponed = std::move(_postponed);
-            try {
-                for (auto& t : postponed) {
-                    auto s = t->schema();
-                    cmlog.debug("resubmitting postponed compaction for table {}.{} [{}]", s->ks_name(), s->cf_name(), fmt::ptr(t));
-                    submit(*t);
-                }
-            } catch (...) {
-                _postponed = std::move(postponed);
+        if (_state != state::enabled) {
+            _postponed.clear();
+            co_return;
+        }
+        auto postponed = std::move(_postponed);
+        try {
+            for (auto& t : postponed) {
+                auto s = t->schema();
+                cmlog.debug("resubmitting postponed compaction for table {}.{} [{}]", s->ks_name(), s->cf_name(), fmt::ptr(t));
+                submit(*t);
             }
+        } catch (...) {
+            _postponed = std::move(postponed);
         }
     }
 }