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diff --git a/impl/src/main/java/io/perfmark/impl/Generator.java b/impl/src/main/java/io/perfmark/impl/Generator.java
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+/*
+ * Copyright 2019 Google LLC
+ *
+ * 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 io.perfmark.impl;
+
+/**
+ * A Generator keeps track of what generation the PerfMark library is on. A generation is a way to
+ * group PerfMark recorded tasks and links together. This allows dynamically enabling and disabling
+ * PerfMark. Each time the library is enabled, a new generation is started and associated with all
+ * the recorded data.
+ *
+ * <p>This class is not threadsafe.  Synchronization is handled externally.
+ *
+ * <p>Normal users are not expected to use this class.
+ */
+public abstract class Generator {
+  /**
+   * This field is here as a hack. This class is a shared dependency of both {@link
+   * SecretPerfMarkImpl} and {@link Storage}. The impl needs to record the first time an event
+   * occurs, but doesn't call Storage#clinit until PerfMark is enabled. This leads to the timings
+   * being off in the trace event viewer, since the "start" time is since it was enabled, rather
+   * than when the first PerfMark call happens.
+   */
+  static final long INIT_NANO_TIME = System.nanoTime();
+
+  /**
+   * This field is also here as a hack, capturing the time the program stated.
+   */
+  static final long INIT_CURRENT_TIME_MILLIS = System.currentTimeMillis();
+
+  /**
+   * The number of reserved bits at the bottom of the generation. All generations should be
+   * left-shifted by this amount.
+   */
+  public static final int GEN_OFFSET = 8;
+  /**
+   * Represents a failure to enable PerfMark library. This can be used by subclasses to indicate a
+   * previous failure to set the generation. It can also be used to indicate the generation count
+   * has overflowed.
+   */
+  public static final long FAILURE = -2L << GEN_OFFSET;
+
+  protected Generator() {}
+
+  /**
+   * Sets the current generation count. This should be eventually noticeable for callers of {@link
+   * #getGeneration()}. An odd number means the library is enabled, while an even number means the
+   * library is disabled.
+   *
+   * @param generation the generation id, shifted left by {@link #GEN_OFFSET}.
+   */
+  public abstract void setGeneration(long generation);
+
+  /**
+   * Gets the current generation, shifted left by {@link #GEN_OFFSET}. An odd number means the
+   * library is enabled, while an even number means the library is disabled.
+   *
+   * @return the current generation or {@link #FAILURE}.
+   */
+  public abstract long getGeneration();
+
+  /**
+   * Returns the approximate cost to change the generation.
+   *
+   * @return an approximate number of nanoseconds needed to change the generator value.
+   */
+  public long costOfSetNanos() {
+    return 1000000;
+  }
+
+  /**
+   * Returns the approximate cost to read the generation.
+   *
+   * @return an approximate number of nanoseconds needed to read the generator value.
+   */
+  public long costOfGetNanos() {
+    return 10;
+  }
+}