move pollers to background threads

SessionMessagingKit/Sending & Receiving/Pollers/ClosedGroupPoller.swift

@@ -89,6 +89,7 @@ public final class ClosedGroupPoller : NSObject {
         SNLog("Next poll interval for closed group with public key: \(groupPublicKey) is \(nextPollInterval) s.")
         timers[groupPublicKey] = Timer.scheduledTimer(withTimeInterval: nextPollInterval, repeats: false) { [weak self] timer in
             timer.invalidate()
+            Threading.closedGroupPollerQueue.async {
                 self?.poll(groupPublicKey).done2 { _ in
                     DispatchQueue.main.async { // Timers don't do well on background queues
                         self?.pollRecursively(groupPublicKey)
@@ -101,6 +102,7 @@ public final class ClosedGroupPoller : NSObject {
                 }
             }
         }
+    }
 
     private func poll(_ groupPublicKey: String) -> Promise<Void> {
         guard isPolling(for: groupPublicKey) else { return Promise.value(()) }

SessionMessagingKit/Sending & Receiving/Pollers/OpenGroupPollerV2.swift

@@ -23,11 +23,11 @@ public final class OpenGroupPollerV2 : NSObject {
             guard let strongSelf = self else { return }
             strongSelf.hasStarted = true
             strongSelf.timer = Timer.scheduledTimer(withTimeInterval: strongSelf.pollInterval, repeats: true) { _ in
-                DispatchQueue.global().async {
+                Threading.openGroupPollerQueue.async {
                     self?.poll().retainUntilComplete()
                 }
             }
-            DispatchQueue.global().async {
+            Threading.openGroupPollerQueue.async {
                 strongSelf.poll().retainUntilComplete()
             }
         }

SessionMessagingKit/Sending & Receiving/Pollers/Poller.swift

@@ -55,7 +55,7 @@ public final class Poller : NSObject {
             guard let strongSelf = self, strongSelf.isPolling else { return }
             Timer.scheduledTimer(withTimeInterval: Poller.retryInterval, repeats: false) { _ in
                 guard let strongSelf = self else { return }
-                DispatchQueue.global().async {
+                Threading.pollerQueue.async {
                     strongSelf.setUpPolling()
                 }
             }

SessionMessagingKit/Utilities/Threading.swift

@@ -3,4 +3,8 @@ import Foundation
 internal enum Threading {
 
     internal static let jobQueue = DispatchQueue(label: "SessionMessagingKit.jobQueue", qos: .userInitiated)
+    
+    internal static let pollerQueue = DispatchQueue(label: "SessionMessagingKit.pollerQueue")
+    internal static let closedGroupPollerQueue = DispatchQueue(label: "SessionMessagingKit.closedGroupPollerQueue")
+    internal static let openGroupPollerQueue = DispatchQueue(label: "SessionMessagingKit.openGroup")
 }