--- old/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java	2020-03-16 16:47:41.102992994 +0800
+++ new/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java	2020-03-16 16:47:40.922993812 +0800
@@ -164,33 +164,57 @@
         return null;
     }
 
+    private static String add_option(String cmd, String opt) {
+       if (cmd.isEmpty()) {
+           return opt;
+       }
+       return cmd + "," + opt;
+    }
+
     private static void histo(String pid, String options)
         throws AttachNotSupportedException, IOException,
                UnsupportedEncodingException {
         String liveopt = "-all";
         String filename = null;
+        String parallelthreadnum = null;
         String subopts[] = options.split(",");
+        boolean set_all = false;
+        boolean set_live = false;
+        String cmdline = "";
 
         for (int i = 0; i < subopts.length; i++) {
             String subopt = subopts[i];
             if (subopt.equals("") || subopt.equals("all")) {
-                // pass
+                cmdline = add_option(cmdline, "-all");
+                set_all = true;
             } else if (subopt.equals("live")) {
-                liveopt = "-live";
+                // Add '-' for compatibility.
+                cmdline = add_option(cmdline, "-live");
+                set_live = true;
             } else if (subopt.startsWith("file=")) {
                 filename = parseFileName(subopt);
                 if (filename == null) {
                     usage(1); // invalid options or no filename
                 }
+                cmdline = add_option(cmdline, filename);
+            } else if (subopt.startsWith("parallelThreadNum=")) {
+               parallelthreadnum = subopt.substring(19);
+               if (parallelthreadnum == null) {
+                    usage(1);
+               }
+               // Add "parallelThreadsNum=<>" for later check
+               cmdline = add_option(cmdline, subopt);
             } else {
                 usage(1);
             }
         }
+        if (set_live && set_all) {
+            usage(1);
+        }
 
         System.out.flush();
-
         // inspectHeap is not the same as jcmd GC.class_histogram
-        executeCommandForPid(pid, "inspectheap", liveopt, filename);
+        executeCommandForPid(pid, "inspectheap", cmdline);
     }
 
     private static void dump(String pid, String options)
@@ -287,6 +311,10 @@
         System.err.println("      live         count only live objects");
         System.err.println("      all          count all objects in the heap (default if one of \"live\" or \"all\" is not specified)");
         System.err.println("      file=<file>  dump data to <file>");
+        System.err.println("      parallelThreadNum=<number>  parallel threads number for heap iteration:");
+        System.err.println("                                  parallelThreadNum=0 default behavior, use predefined number of threads");
+        System.err.println("                                  parallelThreadNum=1 disable parallel heap iteration");
+        System.err.println("                                  parallelThreadNum=<N> use N threads for parallel heap iteration");
         System.err.println("");
         System.err.println("    Example: jmap -histo:live,file=/tmp/histo.data <pid>");
         System.exit(exit);