Thread.dump_to_file time

[Alan Bateman]

On 05/09/2023 12:26, Dr Heinz M. Kabutz wrote:
>
> Hi,
>
> I was wondering about the cost of generating the thread dumps with 
> jcmd Thread.dump_to_file and how this would affect the practicality of 
> finding issues in thread dumps. I thus spun up more and more virtual 
> threads to see how long it would take to call jcmd Thread.dump_to_file.
>
> No surprise that the time is linear. Also no surprise that json is 
> slower to generate than plain.
>
> What did surprise me was how much slower it was to generate these on 
> my MacBookPro vs my server. The machines are roughly the same speed, 
> and my MBP has a very fast SSD. I'm not sure why it would be so slow, 
> but the MBP is approximately 3x slower for generating the dumps:
>
>
The Linux vs. macOS difference is surprising but maybe Andrew's guess 
explains it.

As regards the time then some of it maybe related to the formatter, can 
you try the change below and see if it changes the times?

We have prototyped APIs in this area that would allow 
filtering/de-duplication/processing by in-process tools and agents, 
probably something we will get back to at some point.

-Alan

--- a/src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java
+++ b/src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java
@@ -160,7 +160,7 @@ private static void dumpThread(Thread thread, 
PrintStream ps) {
          String suffix = thread.isVirtual() ? " virtual" : "";
          ps.format("#%d \"%s\"%s%n", thread.threadId(), 
thread.getName(), suffix);
          for (StackTraceElement ste : thread.getStackTrace()) {
-            ps.format("      %s%n", ste);
+            ps.println("      " + ste);
          }
          ps.println();
      }
@@ -263,7 +263,7 @@ private static void dumpThreadToJson(Thread thread, 
PrintStream out, boolean mor
          int i = 0;
          StackTraceElement[] stackTrace = thread.getStackTrace();
          while (i < stackTrace.length) {
-            out.format("              \"%s\"", 
escape(stackTrace[i].toString()));
+            out.println("              \"" + 
escape(stackTrace[i].toString()) + "\"");
              i++;
              if (i < stackTrace.length) {
                  out.println(",");