YARN-11534. Code improvements

Change-Id: Idce41dfff72f0f209683a75b5743672446288f91

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/LinuxContainerExecutor.java

@@ -791,7 +791,7 @@ public boolean signalContainer(ContainerSignalContext ctx)
 
       // In ContainerExecutionException -1 is the default value for the exit code.
       // If it remained unset, we can treat the signalling as interrupted.
-      if (retCode == -1) {
+      if (retCode == ContainerExecutionException.getDefaultExitCode()) {
         throw new InterruptedIOException("Signalling container " + pid + " with "
             + signal + " is interrupted; output: " + e.getOutput() + " and exitCode: "
             + retCode);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/runtime/ContainerExecutionException.java

@@ -87,5 +87,9 @@ public String getOutput() {
   public String getErrorOutput() {
     return errorOutput;
   }
+
+  public static int getDefaultExitCode() {
+    return EXIT_CODE_UNSET;
+  }
 
 }