Minor fixes.

Author: christianhaeubl

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/JfrChunkWriter.java

@@ -422,13 +422,13 @@ private void changeEpoch() {
          */
         @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
         private void processSamplerBuffers() {
-            SubstrateSigprofHandler.singleton().preventThreadsFromEnteringSigProfHandler();
+            SubstrateSigprofHandler.preventThreadsFromEnteringSigProfHandler();
             try {
-                SubstrateSigprofHandler.singleton().waitUntilAllThreadsExitedSignalHandler();
+                SubstrateSigprofHandler.waitUntilAllThreadsExitedSignalHandler();
                 SamplerBuffersAccess.processActiveBuffers();
                 SamplerBuffersAccess.processFullBuffers();
             } finally {
-                SubstrateSigprofHandler.singleton().allowThreadsInSigProfHandler();
+                SubstrateSigprofHandler.allowThreadsInSigProfHandler();
             }
         }
     }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/sampler/SubstrateSigprofHandler.java

@@ -214,22 +214,50 @@ public static SamplerStackWalkVisitor visitor() {
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    boolean isProfilingEnabled() {
-        return enabled;
+    public static void preventThreadsFromEnteringSigProfHandler() {
+        if (ImageSingletons.contains(SubstrateSigprofHandler.class)) {
+            singleton().preventThreadsFromEnteringSigProfHandler0();
+        }
+    }
+
+    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
+    public static void allowThreadsInSigProfHandler() {
+        if (ImageSingletons.contains(SubstrateSigprofHandler.class)) {
+            singleton().allowThreadsInSigProfHandler0();
+        }
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public void preventThreadsFromEnteringSigProfHandler() {
+    public static void waitUntilAllThreadsExitedSignalHandler() {
+        if (ImageSingletons.contains(SubstrateSigprofHandler.class)) {
+            singleton().waitUntilAllThreadsExitedSignalHandler0();
+        }
+    }
+
+    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
+    private void preventThreadsFromEnteringSigProfHandler0() {
         int value = isSignalHandlerDisabledTemporarily.incrementAndGet();
         assert value > 0;
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public void allowThreadsInSigProfHandler() {
+    private void allowThreadsInSigProfHandler0() {
         int value = isSignalHandlerDisabledTemporarily.decrementAndGet();
         assert value >= 0;
     }
 
+    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
+    private void waitUntilAllThreadsExitedSignalHandler0() {
+        while (threadsInSignalHandler.get() > 0) {
+            VMThreads.singleton().yield();
+        }
+    }
+
+    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
+    boolean isProfilingEnabled() {
+        return enabled;
+    }
+
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public SamplerBufferStack availableBuffers() {
         return availableBuffers;
@@ -240,13 +268,6 @@ public SamplerBufferStack fullBuffers() {
         return fullBuffers;
     }
 
-    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public void waitUntilAllThreadsExitedSignalHandler() {
-        while (threadsInSignalHandler.get() > 0) {
-            VMThreads.singleton().yield();
-        }
-    }
-
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     SubstrateThreadMXBean substrateThreadMXBean() {
         return threadMXBean;