Refactor interruptible suppliers into a library package.

These suppliers can exist in lib/supplier since they contain no bazel-specific logic.

PiperOrigin-RevId: 248609626

src/test/java/com/google/devtools/build/lib/supplier/MemoizingInterruptibleSupplierTest.java

diff --git a/src/test/java/com/google/devtools/build/lib/supplier/MemoizingInterruptibleSupplierTest.java b/src/test/java/com/google/devtools/build/lib/supplier/MemoizingInterruptibleSupplierTest.java
new file mode 100644
index 0000000..93967fd
--- /dev/null
+++ b/src/test/java/com/google/devtools/build/lib/supplier/MemoizingInterruptibleSupplierTest.java
@@ -0,0 +1,78 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.supplier;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.testing.GcFinalization;
+import java.lang.ref.WeakReference;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests for {@link MemoizingInterruptibleSupplier}. */
+@RunWith(JUnit4.class)
+public final class MemoizingInterruptibleSupplierTest {
+
+  private int callCount = 0;
+  private String returnVal = "";
+  private CallCounter callCounter = new CallCounter();
+
+  private final class CallCounter {
+    public String call() {
+      ++callCount;
+      return returnVal;
+    }
+  }
+
+  @Test
+  public void returnsCorrectResult() throws Exception {
+    MemoizingInterruptibleSupplier<String> supplier =
+        MemoizingInterruptibleSupplier.of(callCounter::call);
+    returnVal = "abc";
+
+    String result = supplier.get();
+
+    assertThat(result).isEqualTo("abc");
+  }
+
+  @Test
+  public void onlyCallsDelegateOnce() throws Exception {
+    MemoizingInterruptibleSupplier<String> supplier =
+        MemoizingInterruptibleSupplier.of(callCounter::call);
+
+    supplier.get();
+    supplier.get();
+
+    assertThat(callCount).isEqualTo(1);
+  }
+
+  @Test
+  public void freesReferenceToDelegeteAfterGet() throws Exception {
+    MemoizingInterruptibleSupplier<String> supplier =
+        MemoizingInterruptibleSupplier.of(callCounter::call);
+    WeakReference<Object> ref = new WeakReference<>(callCounter);
+    callCounter = null;
+
+    supplier.get();
+
+    GcFinalization.awaitClear(ref);
+  }
+
+  @Test
+  public void of_returnsSameInstanceIfAlreadyMemoizing() {
+    InterruptibleSupplier<String> supplier = MemoizingInterruptibleSupplier.of(callCounter::call);
+    assertThat(MemoizingInterruptibleSupplier.of(supplier)).isSameInstanceAs(supplier);
+  }
+}