RFR: 8291991: Adjust the "shared class paths mismatch" message if class path logging is enabled

[Ioi Lam]

On Thu, 10 Nov 2022 03:29:25 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

> Before this fix, with `-Xshare:on` and `-Xlog:class+path=info` and if there is a class path mismatch, the following error message will be displayed:
> 
> `shared class paths mismatch (hint: enable -Xlog:class+path=info to diagnose the failure)`
> 
> After this fix, only the first part of the error message will be displayed since the "hint" is repetitive if the user has specified `-Xlog:class+path=info.`
> 
> `shared class paths mismatch`
> 
> Passed tiers 1 and 2 testing.

Changes requested by iklam (Reviewer).

src/hotspot/share/cds/filemap.cpp line 1128:

> 1126:       }
> 1127:       if (!log_is_enabled(Info, cds) && !log_is_enabled(Info, class, path)) {
> 1128:         log_warning(cds)("%s %s", mismatch_msg, hint_msg);

Usually, the message is printed inside `fail_continue()`, which goes to `log_info()`. However, in this particular case, we feel that the message is important enough that it should be printed in `log_warning()`. The current implementation is kind of awkward and makes this PR complicated. 

I think we can take this chance to clean things up. We can add an argument to `fail_continue()` to select the logging level. Something like this:


void FileMapInfo::fail_continue(const char *msg, ...) {
  va_list ap;
  va_start(ap, msg);
  fail_continue_impl(LogLevel::Info, msg, ap);
}

void FileMapInfo::fail_continue(LogLevelType level, const char *msg, ...) {
  va_list ap;
  va_start(ap, msg);
  fail_continue_impl(level, msg, ap);
}

void FileMapInfo::fail_continue_impl(LogLevelType level, const char *msg, va_list ap) {
...

-     if (log_is_enabled(Info, cds)) {
-       LogStream ls(Log(cds)::info());
-       ls.print("UseSharedSpaces: "); 
-       ls.vprint_cr(msg, ap);
-     }
+     LogMessage(cds) lm;
+     lm.vwrite(level, msg, ap);
...
}


And thus this function can be simplified as:


const char* mismatch_msg = "shared class paths mismatch";
const char* hint_msg = log_is_enabled(Info, class, path) ?
    "" : " (hint: enable -Xlog:class+path=info to diagnose the failure)";
fail_continue(LogLevel::warning, "%s%s", mismatch_msg, hint_msg);


The "UseSharedSpaces:" is also redundant since the log already contains `[cds]`. It's hard to pass that to `LogMessage` so we may as well just remove it.

-------------

PR: https://git.openjdk.org/jdk/pull/11078