feat Enabled read/write lock for GitHubSanityCachedValue

src/main/java/org/kohsuke/github/GitHubSanityCachedValue.java

@@ -3,6 +3,8 @@
 import org.kohsuke.github.function.SupplierThrows;
 
 import java.time.Instant;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.function.Function;
 
 /**
@@ -12,7 +14,10 @@ class GitHubSanityCachedValue<T> {
 
     private long lastQueriedAtEpochSeconds = 0;
     private T lastResult = null;
-    private final Object lock = new Object();
+    // Allow concurrent readers while a refresh is not needed.
+    private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
+    private final Lock readLock = lock.readLock();
+    private final Lock writeLock = lock.writeLock();
 
     /**
      * Gets the value from the cache or calls the supplier if the cache is empty or out of date.
@@ -26,13 +31,27 @@ class GitHubSanityCachedValue<T> {
      *             the exception thrown by the supplier if it fails.
      */
     <E extends Throwable> T get(Function<T, Boolean> isExpired, SupplierThrows<T, E> query) throws E {
-        synchronized (lock) {
-            if (Instant.now().getEpochSecond() > lastQueriedAtEpochSeconds || isExpired.apply(lastResult)) {
+        readLock.lock();
+        try {
+            boolean expired = Instant.now().getEpochSecond() > lastQueriedAtEpochSeconds || isExpired.apply(lastResult);
+            if (!expired) {
+                return lastResult;
+            }
+        } finally {
+            readLock.unlock();
+        }
+
+        writeLock.lock();
+        try {
+            boolean stillExpired = Instant.now().getEpochSecond() > lastQueriedAtEpochSeconds || isExpired.apply(lastResult);
+            if (stillExpired) {
                 lastResult = query.get();
                 lastQueriedAtEpochSeconds = Instant.now().getEpochSecond();
             }
+            return lastResult;
+        } finally {
+            writeLock.unlock();
         }
-        return lastResult;
     }
 
     /**

src/test/java/org/kohsuke/github/GitHubSanityCachedValueTest.java

@@ -0,0 +1,107 @@
+package org.kohsuke.github;
+
+import org.junit.Test;
+
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+public class GitHubSanityCachedValueTest {
+
+    @Test
+    public void cachesWithinSameSecond() throws Exception {
+        alignToStartOfSecond();
+        GitHubSanityCachedValue<String> cachedValue = new GitHubSanityCachedValue<>();
+        AtomicInteger calls = new AtomicInteger();
+
+        String first = cachedValue.get(() -> {
+            calls.incrementAndGet();
+            return "value";
+        });
+        String second = cachedValue.get(() -> {
+            calls.incrementAndGet();
+            return "value";
+        });
+
+        assertThat(first, equalTo("value"));
+        assertThat(second, equalTo("value"));
+        assertThat(calls.get(), equalTo(1));
+    }
+
+    @Test
+    public void refreshesAfterOneSecond() throws Exception {
+        GitHubSanityCachedValue<String> cachedValue = new GitHubSanityCachedValue<>();
+        AtomicInteger calls = new AtomicInteger();
+
+        String first = cachedValue.get(() -> {
+            calls.incrementAndGet();
+            return "value";
+        });
+
+        Thread.sleep(1100);
+
+        String second = cachedValue.get(() -> {
+            calls.incrementAndGet();
+            return "value";
+        });
+
+        assertThat(first, equalTo("value"));
+        assertThat(second, equalTo("value"));
+        assertThat(calls.get(), equalTo(2));
+    }
+
+    @Test
+    public void concurrentCallersOnlyRefreshOnce() throws Exception {
+        alignToStartOfSecond();
+        GitHubSanityCachedValue<String> cachedValue = new GitHubSanityCachedValue<>();
+        AtomicInteger calls = new AtomicInteger();
+        List<String> results = Collections.synchronizedList(new ArrayList<>());
+        CountDownLatch ready = new CountDownLatch(5);
+        CountDownLatch start = new CountDownLatch(1);
+        CountDownLatch finished = new CountDownLatch(5);
+
+        for (int i = 0; i < 5; i++) {
+            Thread thread = new Thread(() -> {
+                try {
+                    ready.countDown();
+                    start.await();
+                    String value = cachedValue.get((result) -> result == null, () -> {
+                        calls.incrementAndGet();
+                        return "value";
+                    });
+                    results.add(value);
+                } catch (Exception ignored) {
+                    results.add(null);
+                } finally {
+                    finished.countDown();
+                }
+            });
+            thread.start();
+        }
+
+        ready.await();
+        start.countDown();
+        finished.await();
+
+        assertThat(calls.get(), equalTo(1));
+        assertThat(results.size(), equalTo(5));
+        for (String result : results) {
+            assertThat(result, notNullValue());
+            assertThat(result, equalTo("value"));
+        }
+    }
+
+    private static void alignToStartOfSecond() {
+        while (Instant.now().getNano() > 100_000_000) {
+            Thread.yield();
+        }
+    }
+}
+