Summary

Add the options "file=" to JMap -histo to improve JMap's ability

Problem

Currently the "JMap -histo" tool doesn't support to dump result to a file directly.

Solution

Add "file=" option that let JMap -histo to dump directly to file. Please be aware that this is subset of enhancement of JMap More detail please refer to https://bugs.openjdk.java.net/browse/JDK-8214535

Specification

Diff:

--- old/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
+++ new/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
@@ -246,21 +266,27 @@
         System.err.println("        to connect to running process and print class loader statistics");
         System.err.println("    jmap -finalizerinfo <pid>");
         System.err.println("        to connect to running process and print information on objects awaiting finalization");
-        System.err.println("    jmap -histo[:live] <pid>");
+        System.err.println("    jmap -histo[:[<histo-options>]] <pid>");
         System.err.println("        to connect to running process and print histogram of java object heap");
-        System.err.println("        if the \"live\" suboption is specified, only count live objects");
         System.err.println("    jmap -dump:<dump-options> <pid>");
         System.err.println("        to connect to running process and dump java heap");
         System.err.println("    jmap -? -h --help");
         System.err.println("        to print this help message");
         System.err.println("");
         System.err.println("    dump-options:");
-        System.err.println("      live         dump only live objects; if not specified,");
-        System.err.println("                   all objects in the heap are dumped.");
+        System.err.println("      live         dump only live objects");
+        System.err.println("      all          dump all objects in the heap (default if one of \"live\" or \"all\" is not specified);
         System.err.println("      format=b     binary format");
         System.err.println("      file=<file>  dump heap to <file>");
         System.err.println("");
         System.err.println("    Example: jmap -dump:live,format=b,file=heap.bin <pid>");
+        System.err.println("");
+        System.err.println("    histo-options:");
+        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("");
+        System.err.println("    Example: jmap -histo:live,file=/tmp/histo.data <pid>");
         System.exit(exit);
    }   
}

Updated specification:

jmap -clstats <pid>
    to connect to running process and print class loader statistics
jmap -finalizerinfo <pid>
    to connect to running process and print information on objects awaiting finalization
jmap -histo[:<histo-options>] <pid>
    to connect to running process and print histogram of java object heap
jmap -dump:<dump-options> <pid>
    to connect to running process and dump java heap
jmap -? -h --help
    to print this help message

dump-options:
  live         dump only live objects; if not specified, use "all".
  all          all objects in the heap are dumped.
  format=b     binary format
  file=<file>  dump heap to <file>

Example: jmap -dump:live,format=b,file=heap.bin <pid>

histo-options:
  live         only count live objects; if not specified, use "all".
  all          count all objects in the heap
  file=<file>  dump data to <file>

Example: jmap -histo:live,file=/tmp/histo.data <pid>