Make the logging of the memory layout at startup optional

patch by Benjamin Lerer; reviewed by ekaterina Dimitrova for JAMM-58
jbellis · Jul 18, 2023 · 867d781 · 867d781
1 parent 453ffda
commit 867d781
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diff --git a/README.md b/README.md
@@ -270,6 +270,17 @@ Moreover as specified in the `Supported Java versions` section the `ContendedPad
 
 ## Debugging
 
+### Layout and JVM information
+
+The `org.github.jamm.strategies.LogInfoAtStartup` system property can be set to `true` to request Jamm to log at startup in `System.out` information about the JVM and the detected memory layout.
+
+Example of output:
+
+```
+Jamm starting with: java.version='1.8.0_144', java.vendor='Oracle Corporation', instrumentation=true, unsafe=true, Memory Layout: [objectHeaderSize=12 , arrayHeaderSize=16, objectAlignment=8, referenceSize=4, contendedPaddingWidth=128]
+```
+### Visited object tree
+
 In order to see the object tree visited when calling `MemoryMeter.measureDeep` and ensuring that it matches your
 expectations you can build the `MemoryMeter` instance using `printVisitedTree`:
 

diff --git a/src/org/github/jamm/MemoryMeter.java b/src/org/github/jamm/MemoryMeter.java
@@ -39,7 +39,7 @@ public static boolean hasUnsafe() {
     }
 
     public static boolean useStringOptimization() {
-        return StringMeter.ENABLE;
+        return StringMeter.ENABLED;
     }
 
     /**
@@ -418,7 +418,7 @@ public long measureArray(long[] array) {
      */
     public long measureStringDeep(String s) {
 
-        if (StringMeter.ENABLE) {
+        if (StringMeter.ENABLED) {
 
             if (s == null)
                 return 0L;
@@ -471,7 +471,7 @@ public long measureDeep(Object object, ByteBufferMode bbMode) {
             Object current = stack.pop();
 
             // Deal with optimizations first.
-            if (StringMeter.ENABLE && current instanceof String) {
+            if (StringMeter.ENABLED && current instanceof String) {
                 String s = (String) current;
                 long size1 = measureDeep(s, listener);
                 total += size1;

diff --git a/src/org/github/jamm/strategies/MemoryMeterStrategies.java b/src/org/github/jamm/strategies/MemoryMeterStrategies.java
@@ -79,16 +79,27 @@ private static MemoryMeterStrategies createStrategies() {
         MemoryMeterStrategy specStrategy = createSpecStrategy(mayBeIsHiddenMH);
         MemoryMeterStrategy unsafeStrategy = createUnsafeStrategy(mayBeIsHiddenMH, (MemoryLayoutBasedStrategy) specStrategy);
 
+        if (logInformationAtStartup()) {
         // Logging important information once at startup for debugging purpose
-        System.out.println("Jamm starting with: java.version='" + System.getProperty("java.version")
-                            + "', java.vendor='" + System.getProperty("java.vendor")
-                            + "', instrumentation=" + (instrumentationStrategy != null)
-                            + ", unsafe=" + (unsafeStrategy != null)
-                            + ", " + MemoryMeterStrategy.MEMORY_LAYOUT);
+            System.out.println("Jamm starting with: java.version='" + System.getProperty("java.version")
+                                + "', java.vendor='" + System.getProperty("java.vendor")
+                                + "', instrumentation=" + (instrumentationStrategy != null)
+                                + ", unsafe=" + (unsafeStrategy != null)
+                                + ", " + MemoryMeterStrategy.MEMORY_LAYOUT);
+        }
 
         return new MemoryMeterStrategies(instrumentationStrategy, instrumentationAndSpecStrategy, unsafeStrategy, specStrategy);
     }
 
+    /**
+     * Checks if layout and JDK information should be logged at startup.
+     * <p>{@code false} by default to avoid causing issues to existing applications that do not expect that message to be logged.</p>
+     * @return {@code true} if the information should be logged, {@code false} otherwise.
+     */
+    private static boolean logInformationAtStartup() {
+        return Boolean.parseBoolean(System.getProperty("org.github.jamm.strategies.LogInfoAtStartup", "false"));
+    }
+
     private static MemoryMeterStrategy createSpecStrategy(Optional<MethodHandle> mayBeIsHiddenMH) {
 
         if (mayBeIsHiddenMH.isPresent() && !VM.useEmptySlotsInSuper())

diff --git a/src/org/github/jamm/string/StringMeter.java b/src/org/github/jamm/string/StringMeter.java
@@ -23,7 +23,7 @@ public abstract class StringMeter {
     /**
      * Enable or disable string optimization through the {@code org.github.jamm.string.Optimize} String system property. {@code true} by default.
      */
-    public static final boolean ENABLE = Boolean.parseBoolean(System.getProperty("org.github.jamm.string.Optimize", "true"));
+    public static final boolean ENABLED = Boolean.parseBoolean(System.getProperty("org.github.jamm.string.Optimize", "true"));
 
     /**
      * The String shallow size stored as a constant to have it compiled directly into the measure method.

diff --git a/test/org/github/jamm/GuessTest.java b/test/org/github/jamm/GuessTest.java
@@ -38,6 +38,11 @@
 @RunWith(Parameterized.class)
 public class GuessTest {
 
+    @BeforeClass
+    public static void logInfoAtStartup() {
+        System.setProperty("org.github.jamm.strategies.LogInfoAtStartup", "true");
+    }
+
     @Parameterized.Parameters
     public static Collection<MemoryMeter.Guess> guesses() {
 

diff --git a/test/org/github/jamm/MemoryMeterTest.java b/test/org/github/jamm/MemoryMeterTest.java
@@ -7,6 +7,7 @@
 import java.util.function.Predicate;
 
 import org.junit.Assert;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
@@ -17,8 +18,13 @@
 import static org.junit.Assert.assertNotEquals;
 
 @RunWith(Parameterized.class)
-public class MemoryMeterTest
-{
+public class MemoryMeterTest {
+
+    @BeforeClass
+    public static void logInfoAtStartup() {
+        System.setProperty("org.github.jamm.strategies.LogInfoAtStartup", "true");
+    }
+
     @Parameterized.Parameters
     public static Collection<MemoryMeter.Guess> guesses() {
 

diff --git a/test/org/github/jamm/jmh/BenchmarkMeasureInstance.java b/test/org/github/jamm/jmh/BenchmarkMeasureInstance.java
@@ -28,8 +28,8 @@
 @BenchmarkMode(Mode.AverageTime)
 @State(Scope.Thread)
 @OutputTimeUnit(TimeUnit.MICROSECONDS)
-public class BenchmarkMeasureInstance
-{
+public class BenchmarkMeasureInstance {
+
     @Param({"INSTRUMENTATION", "INSTRUMENTATION_AND_SPECIFICATION", "SPECIFICATION", "UNSAFE"})
     private String guess;
 

diff --git a/test/org/github/jamm/strategies/MemoryMeterStrategiesTest.java b/test/org/github/jamm/strategies/MemoryMeterStrategiesTest.java
@@ -4,6 +4,7 @@
 import java.util.Arrays;
 import java.util.List;
 
+import org.junit.BeforeClass;
 import org.junit.Test;
 
 import org.github.jamm.MemoryMeter.Guess;
@@ -16,6 +17,11 @@
 
 public class MemoryMeterStrategiesTest {
 
+    @BeforeClass
+    public static void logInfoAtStartup() {
+        System.setProperty("org.github.jamm.strategies.LogInfoAtStartup", "true");
+    }
+
     @Test
     public void testInvalidEmptyGuessList() {
         MemoryMeterStrategies strategies = MemoryMeterStrategies.getInstance();

diff --git a/test/org/github/jamm/strategies/MemoryMeterStrategyTest.java b/test/org/github/jamm/strategies/MemoryMeterStrategyTest.java
@@ -13,6 +13,7 @@
 
 import org.junit.After;
 import org.junit.Before;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
@@ -34,6 +35,11 @@
 @RunWith(Parameterized.class)
 public class MemoryMeterStrategyTest {
 
+    @BeforeClass
+    public static void logInfoAtStartup() {
+        System.setProperty("org.github.jamm.strategies.LogInfoAtStartup", "true");
+    }
+
     private final MemoryMeter.Guess guess;
 
     private MemoryMeter tested;

diff --git a/test/org/github/jamm/string/StringMeterTest.java b/test/org/github/jamm/string/StringMeterTest.java
@@ -21,6 +21,11 @@
 @RunWith(Parameterized.class)
 public class StringMeterTest {
 
+    @BeforeClass
+    public static void logInfoAtStartup() {
+        System.setProperty("org.github.jamm.strategies.LogInfoAtStartup", "true");
+    }
+
     @BeforeClass
     public static void turnOffStringOptimization() {
         System.setProperty("org.github.jamm.string.Optimize", "false");
@@ -51,6 +56,7 @@ public void testMeasureDeepString() {
                                          "...... really ...... really .... really ... really .... longuer",
                                          "with a chinese character: 我"};
 
+        // The optimization is disabled for the MemoryMeter but not for the StringMeter which does not take into account the ENABLED field.
         MemoryMeter reference = MemoryMeter.builder().withGuessing(MemoryMeter.Guess.INSTRUMENTATION).build();
         assertFalse(MemoryMeter.useStringOptimization());
         StringMeter stringMeter = StringMeter.newInstance();