diff --git a/Mixpanel/AutomaticEvents.swift b/Mixpanel/AutomaticEvents.swift
index 666ca830b..e8b35a489 100644
--- a/Mixpanel/AutomaticEvents.swift
+++ b/Mixpanel/AutomaticEvents.swift
@@ -49,7 +49,7 @@ class AutomaticEvents: NSObject, SKPaymentTransactionObserver, SKProductsRequest
     var hasAddedObserver = false
     var automaticPushTracking = true
     var firstAppOpen = false
-    let awaitingTransactionsWriteLock = DispatchQueue(label: "com.mixpanel.awaiting_transactions_writeLock")
+    let awaitingTransactionsWriteLock = DispatchQueue(label: "com.mixpanel.awaiting_transactions_writeLock", qos: .utility)
 
     func initializeEvents() {
         let firstOpenKey = "MPFirstOpen"
diff --git a/Mixpanel/Flush.swift b/Mixpanel/Flush.swift
index dbcfa680b..8f219ac13 100644
--- a/Mixpanel/Flush.swift
+++ b/Mixpanel/Flush.swift
@@ -43,7 +43,7 @@ class Flush: AppLifecycle {
 
     required init(basePathIdentifier: String) {
         self.flushRequest = FlushRequest(basePathIdentifier: basePathIdentifier)
-        flushIntervalReadWriteLock = DispatchQueue(label: "com.mixpanel.flush_interval.lock", attributes: .concurrent)
+        flushIntervalReadWriteLock = DispatchQueue(label: "com.mixpanel.flush_interval.lock", qos: .utility, attributes: .concurrent)
     }
 
     func flushEventsQueue(_ eventsQueue: Queue, automaticEventsEnabled: Bool?) -> Queue? {
diff --git a/Mixpanel/Mixpanel.swift b/Mixpanel/Mixpanel.swift
index 1c2a9f86b..ff1e5adec 100644
--- a/Mixpanel/Mixpanel.swift
+++ b/Mixpanel/Mixpanel.swift
@@ -132,10 +132,12 @@ class MixpanelManager {
     static let sharedInstance = MixpanelManager()
     private var instances: [String: MixpanelInstance]
     private var mainInstance: MixpanelInstance?
+    private let readWriteLock: ReadWriteLock
 
     init() {
         instances = [String: MixpanelInstance]()
         Logger.addLogging(PrintLogging())
+        readWriteLock = ReadWriteLock(label: "com.mixpanel.instance.manager.lock")
     }
 
     #if !os(OSX) && !WATCH_OS
@@ -152,7 +154,9 @@ class MixpanelManager {
                                         automaticPushTracking: automaticPushTracking,
                                         optOutTrackingByDefault: optOutTrackingByDefault)
         mainInstance = instance
-        instances[instanceName] = instance
+        readWriteLock.write {
+            instances[instanceName] = instance
+        }
 
         return instance
     }
@@ -166,14 +170,20 @@ class MixpanelManager {
                                         name: instanceName,
                                         optOutTrackingByDefault: optOutTrackingByDefault)
         mainInstance = instance
-        instances[instanceName] = instance
+        readWriteLock.write {
+            instances[instanceName] = instance
+        }
 
         return instance
     }
     #endif // os(OSX)
 
     func getInstance(name instanceName: String) -> MixpanelInstance? {
-        guard let instance = instances[instanceName] else {
+        var instance: MixpanelInstance? = nil
+        readWriteLock.read {
+            instance = instances[instanceName]
+        }
+        if instance == nil {
             Logger.warn(message: "no such instance: \(instanceName)")
             return nil
         }
@@ -185,17 +195,23 @@ class MixpanelManager {
     }
 
     func setMainInstance(name instanceName: String) {
-        guard let instance = instances[instanceName] else {
+        var instance: MixpanelInstance? = nil
+        readWriteLock.read {
+            instance = instances[instanceName]
+        }
+        if instance == nil {
             return
         }
         mainInstance = instance
     }
 
     func removeInstance(name instanceName: String) {
-        if instances[instanceName] === mainInstance {
-            mainInstance = nil
+        readWriteLock.write {
+            if instances[instanceName] === mainInstance {
+                mainInstance = nil
+            }
+            instances[instanceName] = nil
         }
-        instances[instanceName] = nil
     }
 
 }
diff --git a/Mixpanel/MixpanelInstance.swift b/Mixpanel/MixpanelInstance.swift
index ae05154f1..9376bde4c 100644
--- a/Mixpanel/MixpanelInstance.swift
+++ b/Mixpanel/MixpanelInstance.swift
@@ -281,7 +281,7 @@ open class MixpanelInstance: CustomDebugStringConvertible, FlushDelegate, AEDele
             self.apiToken = apiToken
         }
         self.name = name
-        self.readWriteLock = ReadWriteLock(label: "globalLock")
+        self.readWriteLock = ReadWriteLock(label: "com.mixpanel.globallock")
         flushInstance = Flush(basePathIdentifier: name)
         #if DECIDE
             decideInstance = Decide(basePathIdentifier: name, lock: self.readWriteLock)
@@ -356,16 +356,16 @@ open class MixpanelInstance: CustomDebugStringConvertible, FlushDelegate, AEDele
             self.apiToken = apiToken
         }
         self.name = name
-        self.readWriteLock = ReadWriteLock(label: "globalLock")
+        self.readWriteLock = ReadWriteLock(label: "com.mixpanel.globallock")
         flushInstance = Flush(basePathIdentifier: name)
         let label = "com.mixpanel.\(self.apiToken)"
-        trackingQueue = DispatchQueue(label: label)
+        trackingQueue = DispatchQueue(label: label, qos: .utility)
         sessionMetadata = SessionMetadata(trackingQueue: trackingQueue)
         trackInstance = Track(apiToken: self.apiToken,
                               lock: self.readWriteLock,
                               metadata: sessionMetadata)
         flushInstance.delegate = self
-        networkQueue = DispatchQueue(label: label)
+        networkQueue = DispatchQueue(label: label, qos: .utility)
         distinctId = defaultDistinctId()
         people = People(apiToken: self.apiToken,
                         serialQueue: trackingQueue,
diff --git a/Mixpanel/ObjectIdentityProvider.swift b/Mixpanel/ObjectIdentityProvider.swift
index 97477eaf2..aad63bd2d 100644
--- a/Mixpanel/ObjectIdentityProvider.swift
+++ b/Mixpanel/ObjectIdentityProvider.swift
@@ -33,7 +33,7 @@ class ObjectIdentityProvider {
 }
 
 class SequenceGenerator {
-    private var queue = DispatchQueue(label: "com.mixpanel.sequence.generator")
+    private var queue = DispatchQueue(label: "com.mixpanel.sequence.generator", qos: .utility)
     private(set) var value: Int32 = 0
     
     init() {
diff --git a/Mixpanel/ReadWriteLock.swift b/Mixpanel/ReadWriteLock.swift
index db363328a..e3a45713d 100644
--- a/Mixpanel/ReadWriteLock.swift
+++ b/Mixpanel/ReadWriteLock.swift
@@ -11,7 +11,7 @@ class ReadWriteLock {
     let concurentQueue: DispatchQueue
 
     init(label: String) {
-        self.concurentQueue = DispatchQueue(label: label, attributes: .concurrent)
+        self.concurentQueue = DispatchQueue(label: label, qos: .utility, attributes: .concurrent)
     }
 
     func read(closure: () -> ()) {
diff --git a/Mixpanel/TweakPersistency.swift b/Mixpanel/TweakPersistency.swift
index 7874d3389..df5c3f39e 100644
--- a/Mixpanel/TweakPersistency.swift
+++ b/Mixpanel/TweakPersistency.swift
@@ -69,7 +69,7 @@ private final class TweakDiskPersistency {
 			.appendingPathExtension("db")
 	}
 
-	private let queue = DispatchQueue(label: "org.khanacademy.swift_tweaks.disk_persistency", attributes: [])
+	private let queue = DispatchQueue(label: "org.khanacademy.swift_tweaks.disk_persistency", qos: .utility, attributes: [])
 
 	init(identifier: String) {
 		self.fileURL = TweakDiskPersistency.fileURLForIdentifier(identifier)
diff --git a/Mixpanel/WebSocketWrapper.swift b/Mixpanel/WebSocketWrapper.swift
index 70e01ef7f..4601e1f39 100644
--- a/Mixpanel/WebSocketWrapper.swift
+++ b/Mixpanel/WebSocketWrapper.swift
@@ -47,7 +47,7 @@ class WebSocketWrapper: WebSocketDelegate {
         open = false
         connected = false
         session = [String: Any]()
-        sessionObjectLock = DispatchQueue(label: "com.mixpanel.session_object_lock", attributes: .concurrent)
+        sessionObjectLock = DispatchQueue(label: "com.mixpanel.session_object_lock", qos: .utility, attributes: .concurrent)
         self.url = url
         self.connectCallback = connectCallback
         self.disconnectCallback = disconnectCallback
diff --git a/MixpanelDemo/MixpanelDemoTests/MixpanelDemoTests.swift b/MixpanelDemo/MixpanelDemoTests/MixpanelDemoTests.swift
index ac018a351..8f0c0c80c 100644
--- a/MixpanelDemo/MixpanelDemoTests/MixpanelDemoTests.swift
+++ b/MixpanelDemo/MixpanelDemoTests/MixpanelDemoTests.swift
@@ -858,7 +858,7 @@ class MixpanelDemoTests: MixpanelBaseTests {
     func testReadWriteLock() {
         var array = [Int]()
         let lock = ReadWriteLock(label: "test")
-        let queue = DispatchQueue(label: "concurrent", attributes: .concurrent)
+        let queue = DispatchQueue(label: "concurrent", qos: .utility, attributes: .concurrent)
         for _ in 0..<10 {
             queue.async {
                 lock.write {