From bb1272d26d30060b205b2effe3b7f35a410134a5 Mon Sep 17 00:00:00 2001
From: Jaroslav Tulach <jaroslav.tulach@enso.org>
Date: Sat, 3 Feb 2024 07:44:31 +0100
Subject: [PATCH] Removing Thread.sleep from Serialization manager code

---
 .../runtime/SerializationPool.java            | 64 ++++++-------------
 1 file changed, 20 insertions(+), 44 deletions(-)

diff --git a/engine/runtime/src/main/java/org/enso/interpreter/runtime/SerializationPool.java b/engine/runtime/src/main/java/org/enso/interpreter/runtime/SerializationPool.java
index e01e755781b2..d71635785c4a 100644
--- a/engine/runtime/src/main/java/org/enso/interpreter/runtime/SerializationPool.java
+++ b/engine/runtime/src/main/java/org/enso/interpreter/runtime/SerializationPool.java
@@ -4,23 +4,14 @@
 import java.util.concurrent.Callable;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
-import java.util.concurrent.LinkedBlockingDeque;
-import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import org.enso.pkg.QualifiedName;
 
 final class SerializationPool {
-  /** The maximum number of serialization threads allowed. */
-  private static final int maximumThreadCount = 2;
-
-  /** The number of threads at compiler start. */
-  private static final int startingThreadCount = maximumThreadCount;
-
-  /** The thread keep-alive time in seconds. */
-  private static final long threadKeepalive = 3;
-
   /** The debug logging level. */
   private static final Level debugLogLevel = Level.FINE;
 
@@ -43,27 +34,13 @@ final class SerializationPool {
       new ConcurrentHashMap<>();
 
   /** The thread pool that handles serialization. */
-  private final ThreadPoolExecutor pool;
+  private final ExecutorService pool;
 
   SerializationPool(TruffleCompilerContext context) {
     this.context = context;
-    this.pool =
-        new ThreadPoolExecutor(
-            startingThreadCount,
-            maximumThreadCount,
-            threadKeepalive,
-            TimeUnit.SECONDS,
-            new LinkedBlockingDeque<Runnable>(),
-            context::createSystemThread);
+    this.pool = Executors.newSingleThreadExecutor(context::createSystemThread);
   }
 
-  /*
-  <E, M > Future<Boolean> doSerialize(Cache<E, M> cache, E entry, boolean useGlobalCacheLocations) {
-    context.saveCache(cache, entry, useGlobalCacheLocations);
-    return null;
-  }
-  */
-
   void prestartAllCoreThreads() {}
 
   /**
@@ -85,10 +62,11 @@ void shutdown(boolean waitForPendingJobCompletion) throws InterruptedException {
     if (!pool.isShutdown()) {
       if (waitForPendingJobCompletion && this.hasJobsRemaining()) {
         int waitingCount;
+        int jobCount;
         synchronized (isWaitingForSerialization) {
           waitingCount = isWaitingForSerialization.size();
+          jobCount = waitingCount + isSerializing.size();
         }
-        var jobCount = waitingCount + isSerializing.size();
         context.logSerializationManager(
             debugLogLevel, "Waiting for #{0} serialization jobs to complete.", jobCount);
 
@@ -97,7 +75,9 @@ void shutdown(boolean waitForPendingJobCompletion) throws InterruptedException {
         int counter = 0;
         while (this.hasJobsRemaining() && counter < maxCount) {
           counter += 1;
-          Thread.sleep(1 * 1000);
+          synchronized (isWaitingForSerialization) {
+            isWaitingForSerialization.wait(1000);
+          }
         }
       }
 
@@ -112,21 +92,10 @@ void shutdown(boolean waitForPendingJobCompletion) throws InterruptedException {
       }
 
       pool.shutdownNow();
-      Thread.sleep(100);
       context.logSerializationManager(debugLogLevel, "Serialization manager has been shut down.");
     }
   }
 
-  /**
-   * Checks if the provided module is in the process of being serialized.
-   *
-   * @param key the module to check
-   * @return `true` if `module` is currently being serialized, `false` otherwise
-   */
-  boolean isSerializing(QualifiedName key) {
-    return isSerializing.containsKey(key);
-  }
-
   boolean isWaitingForSerialization(QualifiedName key) {
     synchronized (isWaitingForSerialization) {
       return isWaitingForSerialization.containsKey(key);
@@ -143,6 +112,7 @@ boolean abort(QualifiedName key) {
     synchronized (isWaitingForSerialization) {
       if (isWaitingForSerialization(key)) {
         var prev = isWaitingForSerialization.remove(key);
+        isWaitingForSerialization.notifyAll();
         if (prev != null) {
           return prev.cancel(false);
         } else {
@@ -157,8 +127,9 @@ boolean abort(QualifiedName key) {
   void startSerializing(QualifiedName name) {
     synchronized (isWaitingForSerialization) {
       isWaitingForSerialization.remove(name);
+      isSerializing.put(name, true);
+      isWaitingForSerialization.notifyAll();
     }
-    isSerializing.put(name, true);
   }
 
   /**
@@ -167,7 +138,10 @@ void startSerializing(QualifiedName name) {
    * @param name the name of the module to set as having finished serialization
    */
   void finishSerializing(QualifiedName name) {
-    isSerializing.remove(name);
+    synchronized (isWaitingForSerialization) {
+      isSerializing.remove(name);
+      isWaitingForSerialization.notifyAll();
+    }
   }
 
   Future<scala.Boolean> submitTask(
@@ -190,8 +164,10 @@ Future<scala.Boolean> submitTask(
   }
 
   void waitWhileSerializing(QualifiedName name) throws InterruptedException {
-    while (isSerializing.containsKey(name)) {
-      Thread.sleep(100);
+    synchronized (isWaitingForSerialization) {
+      while (isSerializing.containsKey(name)) {
+        isWaitingForSerialization.wait(100);
+      }
     }
   }
 }