gaodayue commented on a change in pull request #6402: Thread-safe QueryMetrics
URL: https://github.com/apache/incubator-druid/pull/6402#discussion_r227245253
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File path:
processing/src/main/java/org/apache/druid/query/DefaultQueryMetrics.java
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@@ -24,50 +24,89 @@
import com.google.common.collect.ImmutableMap;
import org.apache.druid.collections.bitmap.BitmapFactory;
import org.apache.druid.java.util.common.StringUtils;
+import org.apache.druid.java.util.emitter.EmittingLogger;
import org.apache.druid.java.util.emitter.service.ServiceEmitter;
import org.apache.druid.java.util.emitter.service.ServiceMetricEvent;
import org.apache.druid.query.filter.Filter;
import org.joda.time.Interval;
+import javax.annotation.concurrent.GuardedBy;
+import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeUnit;
/**
- * DefaultQueryMetrics is unsafe for use from multiple threads. It fails with
RuntimeException on access not from the
- * thread where it was constructed. To "transfer" DefaultQueryMetrics from one
thread to another {@link #ownerThread}
- * field should be updated.
+ * A basic thread-safe implementation of the {@link QueryMetrics} interface.
+ *
+ * <p><b>Note for inheritence:</b> Subclass should override {@link
#makeCopy()} method to return
+ * an instance of that subclass. See {@link
org.apache.druid.query.groupby.DefaultGroupByQueryMetrics}
+ * for an example.
*/
public class DefaultQueryMetrics<QueryType extends Query<?>> implements
QueryMetrics<QueryType>
{
- protected final ObjectMapper jsonMapper;
- protected final ServiceMetricEvent.Builder builder = new
ServiceMetricEvent.Builder();
- protected final Map<String, Number> metrics = new HashMap<>();
+ private static final EmittingLogger log = new
EmittingLogger(DefaultQueryMetrics.class);
- /** Non final to give subclasses ability to reassign it. */
- protected Thread ownerThread = Thread.currentThread();
+ protected final ObjectMapper jsonMapper;
+ protected final Object lock = new Object();
+ @GuardedBy("lock") private final Map<String, String> singleValueDims = new
HashMap<>();
+ @GuardedBy("lock") private final Map<String, String[]> multiValueDims = new
HashMap<>();
+ @GuardedBy("lock") private final Map<String, Number> metrics = new
HashMap<>();
public DefaultQueryMetrics(ObjectMapper jsonMapper)
{
this.jsonMapper = jsonMapper;
}
- protected void checkModifiedFromOwnerThread()
+ // copy constructor, used by makeCopy()
+ public DefaultQueryMetrics(DefaultQueryMetrics that)
{
- if (Thread.currentThread() != ownerThread) {
- throw new IllegalStateException(
- "DefaultQueryMetrics must not be modified from multiple threads. If
it is needed to gather dimension or "
- + "metric information from multiple threads or from an async thread,
this information should explicitly be "
- + "passed between threads (e. g. using Futures), or this
DefaultQueryMetrics's ownerThread should be "
- + "reassigned explicitly");
- }
+ this.jsonMapper = that.jsonMapper;
+ this.singleValueDims.putAll(that.singleValueDims);
+ this.multiValueDims.putAll(that.multiValueDims);
+ this.metrics.putAll(that.metrics);
}
protected void setDimension(String dimension, String value)
{
- checkModifiedFromOwnerThread();
- builder.setDimension(dimension, value);
+ synchronized (lock) {
+ String oldValue = singleValueDims.put(dimension, value);
+ if (oldValue != null && !oldValue.equals(value)) {
Review comment:
I don't think there are cases for setting the same dimensions from multiple
threads. But the overhead to prohibit such usages is a bit high for me. You
needs to maintain the owner thread for each dimension. And I think the checks
in reportMetric and emit are sufficient to catch most bugs.
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