Add ability to experiment between sync and non sync mount item pool

Summary:
After we have unified the implementation of `MountItemPool` between rendercore and litho, we are left with one single difference. Litho used synchronized pools, while rendercore didn't. For the sake of simplicity, we are going to test using non-synchronized pools in Litho as well.

This behavior is only needed for *MountSpecs* as Primitives/Mountables already rely on the render core default.

Reviewed By: zielinskimz

Differential Revision: D48731650

fbshipit-source-id: f8e7635aaa4e16cc585e5ce8db6d47c58c003b8e

litho-core/src/main/java/com/facebook/litho/SpecGeneratedComponent.java

@@ -39,6 +39,7 @@
 import com.facebook.litho.annotations.OnAttached;
 import com.facebook.litho.annotations.OnCreateTreeProp;
 import com.facebook.litho.annotations.OnDetached;
+import com.facebook.litho.config.ComponentsConfiguration;
 import com.facebook.litho.debug.LithoDebugEventAttributes;
 import com.facebook.rendercore.ContentAllocator;
 import com.facebook.rendercore.MountItemsPool;
@@ -776,7 +777,10 @@ public boolean canPreallocate() {
    */
   @Override
   public MountItemsPool.ItemPool onCreateMountContentPool() {
-    return new MountItemsPool.DefaultItemPool(getPoolableContentType(), poolSize(), true);
+    return new MountItemsPool.DefaultItemPool(
+        getPoolableContentType(),
+        poolSize(),
+        ComponentsConfiguration.getDefaultComponentsConfiguration().useSyncMountPools());
   }
 
   @ThreadSafe

litho-core/src/main/java/com/facebook/litho/config/ComponentsConfiguration.java

@@ -324,10 +324,16 @@ public static ComponentsConfiguration.Builder getDefaultComponentsConfigurationB
 
   private final boolean mNestedPreallocationEnabled;
 
+  private final boolean mUseSyncMountPools;
+
   public boolean isNestedPreallocationEnabled() {
     return mNestedPreallocationEnabled;
   }
 
+  public boolean useSyncMountPools() {
+    return mUseSyncMountPools;
+  }
+
   public boolean getUseCancelableLayoutFutures() {
     return mUseCancelableLayoutFutures;
   }
@@ -358,6 +364,7 @@ private ComponentsConfiguration(ComponentsConfiguration.Builder builder) {
     mShouldDisableBgFgOutputs = builder.mShouldDisableBgFgOutputs;
     mUseIncrementalMountGapWorker = builder.mUseIncrementalMountGapWorker;
     mNestedPreallocationEnabled = builder.mNestedPreallocationEnabled;
+    mUseSyncMountPools = builder.mUseSyncItemPools;
   }
 
   public boolean shouldReuseOutputs() {
@@ -396,6 +403,8 @@ public static class Builder {
     boolean mUseIncrementalMountGapWorker = IncrementalMountExtensionConfigs.useGapWorker;
     boolean mNestedPreallocationEnabled = false;
 
+    boolean mUseSyncItemPools = true;
+
     protected Builder() {}
 
     public Builder useCancelableLayoutFutures(boolean enable) {
@@ -438,6 +447,11 @@ public Builder useIncrementalMountGapWorker(boolean enabled) {
       return this;
     }
 
+    public Builder useSyncItemPools(boolean enabled) {
+      mUseSyncItemPools = enabled;
+      return this;
+    }
+
     /**
      * If true, uses the root ComponentTree's mount content allows the usage of the preallocation
      * handler to perform preallocation for nested trees.