[geary/mjog/invert-folder-class-hierarchy: 38/72] Geary.ImapEngine.Email.Prefetcher: Fix the active lock

[Michael Gratton <mjog src gnome org>]

commit 72c0960dbd6c441b0a56fe81db47eddf3c2f4182
Author: Michael Gratton <mike vee net>
Date:   Tue Feb 16 22:19:45 2021 +1100

    Geary.ImapEngine.Email.Prefetcher: Fix the active lock
    
    Make active lock a plain (non-counting) semaphore and ensure it's being
    reset and notified correctly - i.e. reset when anything is queued and
    notified when complete or when there's nothing to do. Don't unlock
    between loading email to prefetch and scheduling them, so that if
    anything is already waiting on the active lock (e.g. sync), the email
    actually gets processed before the lock is released.
    
    Rename property to a generic lock since it's not an external concern
    what kind it is.

 .../imap-engine/imap-engine-email-prefetcher.vala  | 33 ++++++++--------------
 .../imap-engine/imap-engine-minimal-folder.vala    |  2 +-
 2 files changed, 12 insertions(+), 23 deletions(-)
---
diff --git a/src/engine/imap-engine/imap-engine-email-prefetcher.vala 
b/src/engine/imap-engine/imap-engine-email-prefetcher.vala
index a229983b2..dd2e1a2fe 100644
--- a/src/engine/imap-engine/imap-engine-email-prefetcher.vala
+++ b/src/engine/imap-engine/imap-engine-email-prefetcher.vala
@@ -27,8 +27,9 @@ private class Geary.ImapEngine.EmailPrefetcher : Geary.BaseObject {
     private const Geary.Email.Field PREFETCH_FIELDS = Geary.Email.Field.ALL;
     private const int PREFETCH_CHUNK_BYTES = 512 * 1024;
 
-    public Nonblocking.CountingSemaphore active_sem { get; private set;
-        default = new Nonblocking.CountingSemaphore(null); }
+    public Nonblocking.Semaphore active_lock {
+        get; private set; default = new Nonblocking.Semaphore(null);
+    }
 
     private weak ImapEngine.MinimalFolder folder;
     private Nonblocking.Mutex mutex = new Nonblocking.Mutex();
@@ -60,8 +61,7 @@ private class Geary.ImapEngine.EmailPrefetcher : Geary.BaseObject {
         if (this.running.is_cancelled()) {
             this.running = new Cancellable();
 
-            // acquire here since .begin() only schedules for later
-            this.active_sem.acquire();
+            this.active_lock.reset();
             this.do_prepare_all_local_async.begin();
         }
     }
@@ -69,34 +69,25 @@ private class Geary.ImapEngine.EmailPrefetcher : Geary.BaseObject {
     public void close() {
         if (!this.running.is_cancelled()) {
             this.running.cancel();
+            this.prefetch_timer.reset();
 
-            if (this.prefetch_timer.is_running) {
-                this.prefetch_timer.reset();
-                // An acquire was done when the timer was started, so
-                // need to notify if it is still running.
-                this.active_sem.blind_notify();
-            }
+            this.active_lock.blind_notify();
         }
     }
 
     private void on_local_expansion(Gee.Collection<Geary.EmailIdentifier> ids) {
         if (!this.running.is_cancelled()) {
-            // acquire here since .begin() only schedules for later
-            this.active_sem.acquire();
-            do_prepare_new_async.begin(ids);
+            this.active_lock.reset();
+            this.do_prepare_new_async.begin(ids);
         }
     }
 
     private void schedule_prefetch(Gee.Collection<Geary.Email>? emails) {
         if (emails != null && emails.size > 0) {
             this.prefetch_emails.add_all(emails);
-
-            // only increment active state if not rescheduling
-            if (!this.prefetch_timer.is_running) {
-                this.active_sem.acquire();
-            }
-
             this.prefetch_timer.start();
+        } else {
+            this.active_lock.blind_notify();
         }
     }
 
@@ -119,7 +110,6 @@ private class Geary.ImapEngine.EmailPrefetcher : Geary.BaseObject {
         debug("%s: Scheduling %d messages on open for prefetching",
               this.folder.to_string(), list != null ? list.size : 0);
         schedule_prefetch(list);
-        this.active_sem.blind_notify();
     }
 
     private async void do_prepare_new_async(Gee.Collection<Geary.EmailIdentifier> ids) {
@@ -141,7 +131,6 @@ private class Geary.ImapEngine.EmailPrefetcher : Geary.BaseObject {
         debug("%s: Scheduling %d new emails for prefetching",
               this.folder.to_string(), list != null ? list.size : 0);
         schedule_prefetch(list);
-        this.active_sem.blind_notify();
     }
 
     private async void do_prefetch_async() {
@@ -155,7 +144,7 @@ private class Geary.ImapEngine.EmailPrefetcher : Geary.BaseObject {
         }
 
         // this round is done
-        active_sem.blind_notify();
+        this.active_lock.blind_notify();
 
         if (token != Nonblocking.Mutex.INVALID_TOKEN) {
             try {
diff --git a/src/engine/imap-engine/imap-engine-minimal-folder.vala 
b/src/engine/imap-engine/imap-engine-minimal-folder.vala
index 1d0d0e418..3167c3e07 100644
--- a/src/engine/imap-engine/imap-engine-minimal-folder.vala
+++ b/src/engine/imap-engine/imap-engine-minimal-folder.vala
@@ -340,7 +340,7 @@ private class Geary.ImapEngine.MinimalFolder : BaseObject,
 
         // Finally, wait for the prefetcher to have finished
         // downloading the new mail.
-        yield this.email_prefetcher.active_sem.wait_async(cancellable);
+        yield this.email_prefetcher.active_lock.wait_async(cancellable);
     }
 
     private async void check_remote_session() {