Fix an irregularity in BackgroundCleaner::ScheduleCleaning() with

`absl::InfiniteFuture()`: replace the existing scheduled cleaning (to do
nothing) instead of always doing nothing.

PiperOrigin-RevId: 609042280

riegeli/base/background_cleaning.cc

@@ -43,6 +43,7 @@ void BackgroundCleaner::Unregister(Token token) {
 void BackgroundCleaner::CancelCleaning(Token token) {
   absl::MutexLock lock(&mutex_);
   CancelCleaningInternal(token);
+  // Move `token.iter()` anywhere before `next_`.
   if (next_ == token.iter()) {
     ++next_;
   } else {
@@ -64,11 +65,21 @@ inline void BackgroundCleaner::CancelCleaningInternal(Token token) {
       &args));
 }
 
-void BackgroundCleaner::ScheduleCleaningSlow(Token token, absl::Time deadline) {
+void BackgroundCleaner::ScheduleCleaning(Token token, absl::Time deadline) {
   absl::MutexLock lock(&mutex_);
-
-  // Update `entries_` by moving `token.iter()` into the right place, and update
+  // Update `entries_` by moving `token.iter()` to the right place, and update
   // `next_`.
+
+  if (deadline == absl::InfiniteFuture()) {
+    // Move `token.iter()` anywhere before `next_`.
+    if (next_ == token.iter()) {
+      ++next_;
+    } else {
+      entries_.splice(entries_.begin(), entries_, token.iter());
+    }
+    return;
+  }
+
   Entries::iterator iter = entries_.end();
   for (;;) {
     if (iter == next_) {

riegeli/base/background_cleaning.h

@@ -112,8 +112,8 @@ class BackgroundCleaner {
 
   // Schedules cleaning the cleanee corresponding to `token` at `deadline`.
   //
-  // Does nothing if `deadline == absl::InfiniteFuture()`. If `deadline` is in
-  // the past, cleaning will be scheduled.
+  // If `deadline` is `absl::InfiniteFuture()`, cleaning will never happen.
+  // If `deadline` is in the past, cleaning will be scheduled immediately.
   //
   // If `ScheduleCleaning()` is called again for the same cleanee with a pending
   // cleaning, its deadline is replaced.
@@ -131,8 +131,6 @@ class BackgroundCleaner {
   void CancelCleaningInternal(Token token)
       ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  void ScheduleCleaningSlow(Token token, absl::Time deadline);
-
   void BackgroundThread();
 
   absl::Mutex mutex_;
@@ -157,12 +155,6 @@ class BackgroundCleaner {
 
 // Implementation details follow.
 
-inline void BackgroundCleaner::ScheduleCleaning(Token token,
-                                                absl::Time deadline) {
-  if (deadline == absl::InfiniteFuture()) return;
-  ScheduleCleaningSlow(token, deadline);
-}
-
 inline absl::Time BackgroundCleaner::TimeNow() { return absl::Now(); }
 
 }  // namespace riegeli