RFR: 8359827: Test runtime/Thread/ThreadCountLimit.java should run exclusively [v3]

[David Holmes]

On Tue, 22 Jul 2025 12:39:42 GMT, SendaoYan <syan at openjdk.org> wrote:

> The usage of ulimit in this testcase will not cause other concurrent tests to hit the limit, but will cause this test itself do not have enough user processes to start the java.

Sorry - right I get it now. So basically with enough other activity on the machine all the 4096 process/thread capacity may have already been used up before the test can run. It isn't this test that is the "resource hog" as such. What we really want to do is more like `ulimit -u <current process/thread count> + 4096` but getting the current value is tricky.

One possible solution would be to loop so that if we get exitcode 1 then we retry with 4096*2 etc. 

      if (Platform.isLinux()) {
        // On Linux this test sometimes hits the limit for the maximum number of memory mappings,
        // which leads to various other failure modes. Run this test with a limit on how many
        // threads the process is allowed to create, so we hit that limit first. What we want is
        // for another "limit" processes to be available, but ulimit doesn't work that way and
        // if there are already many running processes we could fail to even start the JVM properly.
        // So we loop increasing the limit until we get a successful run. This is not foolproof.
        int pLimit = 4096;
        final String ULIMIT_CMD = "ulimit -u ";
        ProcessBuilder pb = ProcessTools.createTestJavaProcessBuilder(ThreadCountLimit.class.getName());
        String javaCmd = ProcessTools.getCommandLine(pb);
        for (int i = 1; i <= 10; i++) {
            // Relaunch the test with args.length > 0, and the ulimit set
            String cmd = ULIMIT_CMD + Integer.toString(pLimit * i) + " && " + javaCmd + " dummy";
            System.out.println("Trying: bash -c " + cmd);
            OutputAnalyzer oa = ProcessTools.executeCommand("bash", "-c", cmd);
            int exitValue = oa.getExitValue();
            switch (exitValue) {
              case 0: System.out.println("Success!"); return;
              case 1: System.out.println("Retry ..."); continue;
              default: oa.shouldHaveExitValue(0); // generate error report
            }
        }
        throw new Error("Failed to perform a successful run!");
      } else {
        // Not Linux so run directly.
        test();
      }

Took 5 loops to run on my system (ulimit -u 24576) when I had an unrestricted version of the test running which has about 20700 live threads.

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PR Comment: https://git.openjdk.org/jdk/pull/26401#issuecomment-3104913285