[GitHub] kiszk commented on a change in pull request #23278: [SPARK-24920][Core] Allow sharing Netty's memory pool allocators

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kiszk commented on a change in pull request #23278: [SPARK-24920][Core] Allow sharing Netty's memory pool allocators
URL: https://github.com/apache/spark/pull/23278#discussion_r241941523
 
 

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 File path: common/network-common/src/main/java/org/apache/spark/network/util/NettyUtils.java
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 @@ -95,6 +111,38 @@ public static String getRemoteAddress(Channel channel) {
     return "<unknown remote>";
   }
 
+  /**
+   * Returns the default number of threads for both the Netty client and server thread pools.
+   * If numUsableCores is 0, we will use Runtime get an approximate number of available cores.
+   */
+  public static int defaultNumThreads(int numUsableCores) {
+    final int availableCores;
+    if (numUsableCores > 0) {
+      availableCores = numUsableCores;
+    } else {
+      availableCores = Runtime.getRuntime().availableProcessors();
+    }
+    return Math.min(availableCores, MAX_DEFAULT_NETTY_THREADS);
+  }
+
+  /**
+   * Returns the lazily created shared pooled ByteBuf allocator for the specified allowCache
+   * parameter value.
+   */
+  public static synchronized PooledByteBufAllocator getSharedPooledByteBufAllocator(
 
 Review comment:
   If you will use volatile, this code must use two `volatile` instance variables instead of one array. This is because `volatile PooledByteBufAllocator _s[]` is effective only for `_s` rather than `_s[0], _s[1], ...`.

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