Auto-detect Android and use an Android-friendly IdGenerator instance. (…

…#3176)

* Auto-detect Android and use an Android-friendly IdGenerator instance.

* simplify the random initialization

* Make the AndroidFriendlyRandomIdGenerator even simpler by just keeping a single Random instance

sdk/trace/src/main/java/io/opentelemetry/sdk/trace/AndroidFriendlyRandomIdGenerator.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.trace;
+
+import io.opentelemetry.api.trace.SpanId;
+import io.opentelemetry.api.trace.TraceId;
+import java.util.Random;
+
+/**
+ * {@link IdGenerator} instance that doesn't use {@link java.util.concurrent.ThreadLocalRandom},
+ * which is broken on most versions of Android (it uses the same seed everytime it starts up).
+ */
+enum AndroidFriendlyRandomIdGenerator implements IdGenerator {
+  INSTANCE;
+
+  private static final Random random = new Random();
+
+  private static final long INVALID_ID = 0;
+
+  @Override
+  public String generateSpanId() {
+    long id;
+    do {
+      id = random.nextLong();
+    } while (id == INVALID_ID);
+    return SpanId.fromLong(id);
+  }
+
+  @Override
+  public String generateTraceId() {
+    long idHi;
+    long idLo;
+    do {
+      idHi = random.nextLong();
+      idLo = random.nextLong();
+    } while (idHi == INVALID_ID && idLo == INVALID_ID);
+    return TraceId.fromLongs(idHi, idLo);
+  }
+}

sdk/trace/src/main/java/io/opentelemetry/sdk/trace/IdGenerator.java

@@ -21,6 +21,10 @@ public interface IdGenerator {
    * randomness but may change in the future.
    */
   static IdGenerator random() {
+    // note: check borrowed from OkHttp's check for Android.
+    if ("Dalvik".equals(System.getProperty("java.vm.name"))) {
+      return AndroidFriendlyRandomIdGenerator.INSTANCE;
+    }
     return RandomIdGenerator.INSTANCE;
   }
 

sdk/trace/src/test/java/io/opentelemetry/sdk/trace/RandomIdGeneratorTest.java

@@ -19,11 +19,25 @@ void defaults() {
 
     // Can't assert values but can assert they're valid, try a lot as a sort of fuzz check.
     for (int i = 0; i < 1000; i++) {
-      CharSequence traceId = generator.generateTraceId();
-      assertThat(traceId.toString()).isNotEqualTo(TraceId.getInvalid());
+      String traceId = generator.generateTraceId();
+      assertThat(traceId).isNotEqualTo(TraceId.getInvalid());
 
-      CharSequence spanId = generator.generateSpanId();
-      assertThat(spanId.toString()).isNotEqualTo(SpanId.getInvalid());
+      String spanId = generator.generateSpanId();
+      assertThat(spanId).isNotEqualTo(SpanId.getInvalid());
+    }
+  }
+
+  @Test
+  void androidVersion() {
+    IdGenerator generator = AndroidFriendlyRandomIdGenerator.INSTANCE;
+
+    // Can't assert values but can assert they're valid, try a lot as a sort of fuzz check.
+    for (int i = 0; i < 1000; i++) {
+      String traceId = generator.generateTraceId();
+      assertThat(traceId).isNotEqualTo(TraceId.getInvalid());
+
+      String spanId = generator.generateSpanId();
+      assertThat(spanId).isNotEqualTo(SpanId.getInvalid());
     }
   }
 }