[syncback] Reuse currently open box if possible

Summary:
Previously we would unconditionally issue a SELECT when openBox was
called. Now we check if the currently open box is the one we want first and
return immediately if it is, avoiding the unnecessary SELECT (which can be
quite expensive on large folders like INBOX). We were also calling closeBox
after iterating all the messages in a thread to mark them as read/unread.
This was unnecessary and was causing extra SELECTs to be issued. Now we don't!
This diff is a 5x speedup over the old behavior when marking lots of
threads in the same folder as read all at once.

Test Plan: Run locally, measure perf with log statements

Reviewers: evan, juan

Reviewed By: evan, juan

Differential Revision: https://phab.nylas.com/D3654

packages/isomorphic-core/src/imap-connection.js

@@ -196,6 +196,9 @@ class IMAPConnection extends EventEmitter {
     if (!this._imap) {
       throw new IMAPConnectionNotReadyError(`IMAPConnection::openBox`)
     }
+    if (folderName === this.getOpenBoxName()) {
+      return Promise.resolve(new IMAPBox(this, this._imap._box));
+    }
     this._isOpeningBox = true
     return this.createConnectionPromise((resolve, reject) => {
       return this._imap.openBoxAsync(folderName, readOnly)

packages/local-sync/src/local-sync-worker/sync-worker.es6

@@ -319,6 +319,7 @@ class SyncWorker {
   }
 
   async _runSyncbackTask(task) {
+    const before = new Date();
     const syncbackRequest = task.syncbackRequestObject();
     console.log(`🔃 📤 ${task.description()}`, syncbackRequest.props)
     try {
@@ -330,11 +331,13 @@ class SyncWorker {
       const responseJSON = await this._conn.runOperation(task);
       syncbackRequest.status = "SUCCEEDED";
       syncbackRequest.responseJSON = responseJSON || {};
-      console.log(`🔃 📤 ${task.description()} Succeeded`)
+      const after = new Date();
+      console.log(`🔃 📤 ${task.description()} Succeeded (${after.getTime() - before.getTime()}ms)`)
     } catch (error) {
       syncbackRequest.error = error;
       syncbackRequest.status = "FAILED";
-      console.error(`🔃 📤 ${task.description()} Failed`, {syncbackRequest: syncbackRequest.toJSON()})
+      const after = new Date();
+      console.error(`🔃 📤 ${task.description()} Failed (${after.getTime() - before.getTime()}ms)`, {syncbackRequest: syncbackRequest.toJSON()})
     } finally {
       await syncbackRequest.save();
     }

packages/local-sync/src/local-sync-worker/syncback_tasks/task-helpers.js

@@ -18,7 +18,7 @@ const TaskHelpers = {
         imap.openBox(category.name, {readOnly: false}).then((box) =>
           Promise.all(msgsInCategories[category.id].map((message) =>
             callback({message, category, box})
-          )).then(() => box.closeBox())
+          ))
         )
       )
     })