From 61aa66b558ae8f2987a238216ac01e375f195c1e Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Tue, 17 Jan 2023 01:33:44 +0800
Subject: Make ParallelSupplier a top-level class.

---
 .../keuin/kbackupfabric/util/ParallelSupplier.java | 81 ++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 src/main/java/com/keuin/kbackupfabric/util/ParallelSupplier.java

(limited to 'src/main/java/com/keuin/kbackupfabric/util/ParallelSupplier.java')

diff --git a/src/main/java/com/keuin/kbackupfabric/util/ParallelSupplier.java b/src/main/java/com/keuin/kbackupfabric/util/ParallelSupplier.java
new file mode 100644
index 0000000..bd51711
--- /dev/null
+++ b/src/main/java/com/keuin/kbackupfabric/util/ParallelSupplier.java
@@ -0,0 +1,81 @@
+package com.keuin.kbackupfabric.util;
+
+import com.keuin.kbackupfabric.backup.incremental.ObjectCollectionFactory;
+
+import java.util.HashSet;
+import java.util.Optional;
+import java.util.Queue;
+import java.util.Set;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+
+/**
+ * A single-consumer, multiple-producer model.
+ *
+ * @param <Res> type of the resource to be produced and consumed.
+ */
+public class ParallelSupplier<Res> {
+
+    private final Consumer<Res> consumer;
+    private final ConcurrentLinkedQueue<Supplier<Res>> taskList = new ConcurrentLinkedQueue<>();
+    private final int threads;
+    private final Set<ParallelWorker<Res>> workers = new HashSet<>();
+
+    public ParallelSupplier(Consumer<Res> consumer, int threads) {
+        this.consumer = consumer;
+        this.threads = threads;
+    }
+
+    public void addTask(Supplier<Res> valueSupplier) {
+        this.taskList.add(valueSupplier);
+    }
+
+    public void process() {
+        workers.clear();
+        for (int i = 0; i < threads; i++) {
+            ParallelWorker<Res> worker = new ParallelWorker<>(taskList, consumer, i);
+            workers.add(worker);
+            worker.start();
+        }
+        join(); // wait for all workers to exit before returning
+    }
+
+    private void join() {
+        while (true) {
+            int aliveCount = 0;
+            for (ParallelWorker<Res> worker : workers) {
+                try {
+                    if (worker.isAlive()) {
+                        ++aliveCount;
+                        worker.join();
+                    }
+                } catch (InterruptedException ignored) {
+                }
+            }
+            if (aliveCount == 0)
+                return;
+        }
+    }
+
+    private static class ParallelWorker<V> extends Thread {
+
+        private final Queue<Supplier<V>> taskProvider;
+        private final Consumer<V> consumer;
+
+        public ParallelWorker(Queue<Supplier<V>> taskProvider, Consumer<V> consumer, int workerId) {
+            super("PutterWorker#" + workerId);
+            this.taskProvider = taskProvider;
+            this.consumer = consumer;
+        }
+
+        @Override
+        public void run() {
+            Supplier<V> supplier;
+            while ((supplier = taskProvider.poll()) != null) {
+                // here we do not let the consumer accept null productions
+                Optional.ofNullable(supplier.get()).ifPresent(consumer);
+            }
+        }
+    }
+}
-- 
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