Core pool size

app/src/main/java/eu/faircode/email/AdapterMessage.java

@@ -7811,7 +7811,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
         };
 
         AsyncDifferConfig<TupleMessageEx> config = new AsyncDifferConfig.Builder<>(callback)
-                .setBackgroundThreadExecutor(Helper.getBackgroundExecutor(2, "differ"))
+                .setBackgroundThreadExecutor(Helper.getBackgroundExecutor(0, 2, 3, "differ"))
                 .build();
         this.differ = new AsyncPagedListDiffer<>(new AdapterListUpdateCallback(this), config);
         this.differ.addPagedListListener(new AsyncPagedListDiffer.PagedListListener<TupleMessageEx>() {

app/src/main/java/eu/faircode/email/Helper.java

@@ -281,6 +281,10 @@ public class Helper {
     }
 
     static ExecutorService getBackgroundExecutor(int threads, final String name) {
+        return getBackgroundExecutor(threads, threads, 0, name);
+    }
+
+    static ExecutorService getBackgroundExecutor(int min, int max, int keepalive, final String name) {
         ThreadFactory factory = new ThreadFactory() {
             private final AtomicInteger threadId = new AtomicInteger();
 
@@ -293,7 +297,7 @@ public class Helper {
             }
         };
 
-        if (threads == 0) {
+        if (max == 0) {
             // java.lang.OutOfMemoryError: pthread_create (1040KB stack) failed: Try again
             // 1040 KB native stack size / 32 KB thread stack size ~ 32 threads
             int processors = Runtime.getRuntime().availableProcessors(); // Modern devices: 8
@@ -304,11 +308,11 @@ public class Helper {
                     3L, TimeUnit.SECONDS,
                     new LinkedBlockingQueue<Runnable>(),
                     factory);
-        } else if (threads == 1)
+        } else if (max == 1)
             return new ThreadPoolExecutorEx(
                     name,
-                    threads, threads,
-                    0L, TimeUnit.MILLISECONDS,
+                    min, max,
+                    keepalive, TimeUnit.SECONDS,
                     new PriorityBlockingQueue<Runnable>(10, new PriorityComparator()),
                     factory) {
                 private final AtomicLong sequenceId = new AtomicLong();
@@ -327,8 +331,8 @@ public class Helper {
         else
             return new ThreadPoolExecutorEx(
                     name,
-                    threads, threads,
-                    0L, TimeUnit.MILLISECONDS,
+                    min, max,
+                    keepalive, TimeUnit.SECONDS,
                     new LinkedBlockingQueue<Runnable>(),
                     factory);
     }