diff --git a/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/AttachmentCancelClickListener.kt b/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/AttachmentCancelClickListener.kt
index 0a1c612243..cab7c620a7 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/AttachmentCancelClickListener.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/AttachmentCancelClickListener.kt
@@ -5,6 +5,8 @@
 package org.thoughtcrime.securesms.conversation.clicklisteners
 
 import android.view.View
+import kotlinx.collections.immutable.toPersistentList
+import org.signal.core.util.concurrent.SignalExecutors
 import org.signal.core.util.logging.Log
 import org.thoughtcrime.securesms.attachments.DatabaseAttachment
 import org.thoughtcrime.securesms.dependencies.AppDependencies
@@ -14,27 +16,37 @@ import org.thoughtcrime.securesms.jobs.AttachmentUploadJob
 import org.thoughtcrime.securesms.mms.Slide
 import org.thoughtcrime.securesms.mms.SlidesClickedListener
 
+/**
+ * Cancels all attachments passed through to the callback.
+ *
+ * Creates a persistent copy of the handed list of slides to prevent off-thread
+ * manipulation.
+ */
 internal class AttachmentCancelClickListener : SlidesClickedListener {
-  override fun onClick(v: View, slides: List<Slide>) {
-    Log.i(TAG, "Canceling compression/upload/download jobs for ${slides.size} items")
-    val jobManager = AppDependencies.jobManager
-    var cancelCount = 0
-    for (slide in slides) {
-      val attachmentId = (slide.asAttachment() as DatabaseAttachment).attachmentId
-      val jobsToCancel = jobManager.find {
-        when (it.factoryKey) {
-          AttachmentDownloadJob.KEY -> AttachmentDownloadJob.jobSpecMatchesAttachmentId(it, attachmentId)
-          AttachmentCompressionJob.KEY -> AttachmentCompressionJob.jobSpecMatchesAttachmentId(it, attachmentId)
-          AttachmentUploadJob.KEY -> AttachmentUploadJob.jobSpecMatchesAttachmentId(it, attachmentId)
-          else -> false
+  override fun onClick(unused: View, slides: List<Slide>) {
+    val toCancel = slides.toPersistentList()
+
+    Log.i(TAG, "Canceling compression/upload/download jobs for ${toCancel.size} items")
+
+    SignalExecutors.BOUNDED_IO.execute {
+      var cancelCount = 0
+      for (slide in toCancel) {
+        val attachmentId = (slide.asAttachment() as DatabaseAttachment).attachmentId
+        val jobsToCancel = AppDependencies.jobManager.find {
+          when (it.factoryKey) {
+            AttachmentDownloadJob.KEY -> AttachmentDownloadJob.jobSpecMatchesAttachmentId(it, attachmentId)
+            AttachmentCompressionJob.KEY -> AttachmentCompressionJob.jobSpecMatchesAttachmentId(it, attachmentId)
+            AttachmentUploadJob.KEY -> AttachmentUploadJob.jobSpecMatchesAttachmentId(it, attachmentId)
+            else -> false
+          }
+        }
+        jobsToCancel.forEach {
+          AppDependencies.jobManager.cancel(it.id)
+          cancelCount++
         }
       }
-      jobsToCancel.forEach {
-        jobManager.cancel(it.id)
-        cancelCount++
-      }
+      Log.i(TAG, "Canceled $cancelCount jobs.")
     }
-    Log.i(TAG, "Canceled $cancelCount jobs.")
   }
 
   companion object {
diff --git a/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/ResendClickListener.kt b/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/ResendClickListener.kt
index 60dede9140..c00b7f4fde 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/ResendClickListener.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/conversation/clicklisteners/ResendClickListener.kt
@@ -6,6 +6,7 @@
 package org.thoughtcrime.securesms.conversation.clicklisteners
 
 import android.view.View
+import org.signal.core.util.concurrent.SignalExecutors
 import org.signal.core.util.logging.Log
 import org.thoughtcrime.securesms.database.model.MessageRecord
 import org.thoughtcrime.securesms.mms.Slide
@@ -19,7 +20,9 @@ class ResendClickListener(private val messageRecord: MessageRecord) : SlidesClic
       return
     }
 
-    MessageSender.resend(v.context, messageRecord)
+    SignalExecutors.BOUNDED.execute {
+      MessageSender.resend(v.context, messageRecord)
+    }
   }
 
   companion object {
diff --git a/app/src/main/java/org/thoughtcrime/securesms/jobmanager/JobManager.java b/app/src/main/java/org/thoughtcrime/securesms/jobmanager/JobManager.java
index 3be335af51..cdc1ab318d 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/jobmanager/JobManager.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/jobmanager/JobManager.java
@@ -288,6 +288,7 @@ public class JobManager implements ConstraintObserver.Notifier {
    * Search through the list of pending jobs and find all that match a given predicate. Note that there will always be races here, and the result you get back
    * may not be valid anymore by the time you get it. Use with caution.
    */
+  @WorkerThread
   public @NonNull List<JobSpec> find(@NonNull Predicate<JobSpec> predicate) {
     waitUntilInitialized();
     return jobController.findJobs(predicate);
diff --git a/app/src/main/java/org/thoughtcrime/securesms/sms/MessageSender.java b/app/src/main/java/org/thoughtcrime/securesms/sms/MessageSender.java
index c76c30cdf3..8789ce585a 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/sms/MessageSender.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/sms/MessageSender.java
@@ -478,6 +478,7 @@ public class MessageSender {
     onMessageSent();
   }
 
+  @WorkerThread
   public static void resend(Context context, MessageRecord messageRecord) {
     long       messageId   = messageRecord.getId();
     boolean    forceSms    = messageRecord.isForcedSms();
@@ -517,6 +518,7 @@ public class MessageSender {
     return outgoingMessage;
   }
 
+  @WorkerThread
   private static void sendMessageInternal(Context context,
                                           Recipient recipient,
                                           SendType sendType,
@@ -534,6 +536,7 @@ public class MessageSender {
     }
   }
 
+  @WorkerThread
   private static void sendMediaPush(Context context, Recipient recipient, long messageId, @NonNull Collection<String> uploadJobIds) {
     JobManager jobManager = AppDependencies.getJobManager();
 
@@ -545,6 +548,7 @@ public class MessageSender {
     }
   }
 
+  @WorkerThread
   private static void sendGroupPush(@NonNull Context context, @NonNull Recipient recipient, long messageId, @NonNull Set<RecipientId> filterRecipientIds, @NonNull Collection<String> uploadJobIds) {
     JobManager jobManager = AppDependencies.getJobManager();
 
@@ -556,6 +560,7 @@ public class MessageSender {
     }
   }
 
+  @WorkerThread
   private static void sendDistributionList(@NonNull Context context, @NonNull Recipient recipient, long messageId, @NonNull Set<RecipientId> filterRecipientIds, @NonNull Collection<String> uploadJobIds) {
     JobManager jobManager = AppDependencies.getJobManager();