From 5c58089fb7b1c88fa5cfbb7cc877a2675eb6941b Mon Sep 17 00:00:00 2001
From: Michal Horejsek <horejsek@protonmail.com>
Date: Mon, 7 Dec 2020 14:14:45 +0100
Subject: [PATCH] Do not unpause event loop if other mailbox is still fetching

---
 internal/imap/mailbox_messages.go |  4 ++--
 internal/imap/user.go             | 38 +++++++++++++++++++++++++++----
 unreleased.md                     |  1 +
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/internal/imap/mailbox_messages.go b/internal/imap/mailbox_messages.go
index 232dc114..c52fdf18 100644
--- a/internal/imap/mailbox_messages.go
+++ b/internal/imap/mailbox_messages.go
@@ -454,8 +454,8 @@ func (im *imapMailbox) ListMessages(isUID bool, seqSet *imap.SeqSet, items []ima
 	// EXPUNGE cannot be sent during listing and can come only from
 	// the event loop, so we prevent any server side update to avoid
 	// the problem.
-	im.storeUser.PauseEventLoop(true)
-	defer im.storeUser.PauseEventLoop(false)
+	im.user.pauseEventLoop()
+	defer im.user.unpauseEventLoop()
 
 	var markAsReadIDs []string
 	markAsReadMutex := &sync.Mutex{}
diff --git a/internal/imap/user.go b/internal/imap/user.go
index 5647b14c..a4c72842 100644
--- a/internal/imap/user.go
+++ b/internal/imap/user.go
@@ -42,11 +42,9 @@ type imapUser struct {
 	currentAddressLowercase string
 
 	appendInProcess sync.WaitGroup
-}
 
-// This method should eventually no longer be necessary. Everything should go via store.
-func (iu *imapUser) client() pmapi.Client {
-	return iu.user.GetTemporaryPMAPIClient()
+	eventLoopPausingCounter int
+	eventLoopPausingLocker  sync.Locker
 }
 
 // newIMAPUser returns struct implementing go-imap/user interface.
@@ -78,9 +76,41 @@ func newIMAPUser(
 		storeAddress: storeAddress,
 
 		currentAddressLowercase: strings.ToLower(address),
+
+		eventLoopPausingLocker: &sync.Mutex{},
 	}, err
 }
 
+// This method should eventually no longer be necessary. Everything should go via store.
+func (iu *imapUser) client() pmapi.Client {
+	return iu.user.GetTemporaryPMAPIClient()
+}
+
+// pauseEventLoop pauses event loop and increases the number of mailboxes which
+// is performing action forbidding event loop to run (such as FETCH which needs
+// UIDs to be stable and thus EXPUNGE cannot be done during the request).
+func (iu *imapUser) pauseEventLoop() {
+	iu.eventLoopPausingLocker.Lock()
+	defer iu.eventLoopPausingLocker.Unlock()
+
+	iu.eventLoopPausingCounter++
+	iu.storeUser.PauseEventLoop(true)
+}
+
+// unpauseEventLoop unpauses event loop but only if no other request is not
+// performing action forbidding event loop to run (see pauseEventLoop).
+func (iu *imapUser) unpauseEventLoop() {
+	iu.eventLoopPausingLocker.Lock()
+	defer iu.eventLoopPausingLocker.Unlock()
+
+	if iu.eventLoopPausingCounter > 0 {
+		iu.eventLoopPausingCounter--
+	}
+	if iu.eventLoopPausingCounter == 0 {
+		iu.storeUser.PauseEventLoop(false)
+	}
+}
+
 func (iu *imapUser) isSubscribed(labelID string) bool {
 	subscriptionExceptions := iu.backend.getCacheList(iu.storeUser.UserID(), SubscriptionException)
 	exceptions := strings.Split(subscriptionExceptions, ";")
diff --git a/unreleased.md b/unreleased.md
index 30833ccc..e47b6b63 100644
--- a/unreleased.md
+++ b/unreleased.md
@@ -52,3 +52,4 @@ Changelog [format](http://keepachangelog.com/en/1.0.0/)
 
 ### Fixed
 * GODT-900 Remove \Deleted flag after re-importing the message (do not delete messages by moving to local folder and back).
+* GODT-908 Do not unpause event loop if other mailbox is still fetching.