[geary] Prevent AccountSynchronizier from deadlocking under certain conditions

[Jim Nelson <jnelson src gnome org>]

commit 201af223c2cd7265ec60b4a1f608405d264f9351
Author: Jim Nelson <jim yorba org>
Date:   Mon Apr 21 11:17:03 2014 -0700

    Prevent AccountSynchronizier from deadlocking under certain conditions
    
    The AccountSynchronizer could deadlock waiting for an EmailPrefetcher
    to finish under certain conditions, particularly if the folder closed
    before the prefetcher was finished.  This lead to a state where the
    AccountSynchronizer would never synchronize against unopened folders.
    If Geary was left open for a long time and the user clicked on All
    Mail, rather than the current state of that folder appearing
    immediately, it could take a moment for Geary to fetch the envelopes
    and headers/bodies.
    
    Fixing this closes bgo#713447, which was also due to other bugs that
    have been fixed over time (in particular, the startup speedup work in
    0.5) and better spinner management (bgo#713703).  It also corrects
    a problem where detection of new mail while opening the folder let
    to prefetching that mail, which was unnecessary because once the
    folder is fully opened all unsynchronized mail is detected and pulled
    down.

 .../imap-engine/imap-engine-email-prefetcher.vala  |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/src/engine/imap-engine/imap-engine-email-prefetcher.vala 
b/src/engine/imap-engine/imap-engine-email-prefetcher.vala
index 4fd3a47..76c36dc 100644
--- a/src/engine/imap-engine/imap-engine-email-prefetcher.vala
+++ b/src/engine/imap-engine/imap-engine-email-prefetcher.vala
@@ -70,10 +70,18 @@ private class Geary.ImapEngine.EmailPrefetcher : Object {
         if (schedule_id != 0) {
             Source.remove(schedule_id);
             schedule_id = 0;
+            
+            // since an acquire was done when scheduled, need to notify when cancelled
+            active_sem.blind_notify();
         }
     }
     
     private void on_local_expansion(Gee.Collection<Geary.EmailIdentifier> ids) {
+        // it's possible to be notified of an append prior to remote open; don't prefetch until
+        // that occurs
+        if (folder.get_open_state() != Geary.Folder.OpenState.BOTH)
+            return;
+        
         // acquire here since .begin() only schedules for later
         active_sem.acquire();
         do_prepare_new_async.begin(ids);