src/hotspot/share/gc/shared/gcLogPrecious.cpp

/*
 * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

#include "gc/shared/gcLogPrecious.hpp"
#include "runtime/mutex.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/os.hpp"
#include "utilities/ostream.hpp"

stringStream* GCLogPrecious::_lines = nullptr;
stringStream* GCLogPrecious::_temp = nullptr;
Mutex* GCLogPrecious::_lock = nullptr;

void GCLogPrecious::initialize() {
  _lines = new (mtGC) stringStream();
  _temp = new (mtGC) stringStream();
  _lock = new Mutex(Mutex::event, /* The lowest lock rank I could find */
                    "GCLogPrecious Lock");
}

void GCLogPrecious::vwrite_inner(LogTargetHandle log, const char* format, va_list args) {
  // Generate the string in the temp buffer
  _temp->reset();
  _temp->vprint(format, args);

  // Save it in the precious lines buffer
  _lines->print_cr(" %s", _temp->base());

  // Log it to UL
  log.print("%s", _temp->base());

  // Leave _temp buffer to be used by vwrite_and_debug
}

void GCLogPrecious::vwrite(LogTargetHandle log, const char* format, va_list args) {
  MutexLocker locker(_lock, Mutex::_no_safepoint_check_flag);
  vwrite_inner(log, format, args);
}

void GCLogPrecious::vwrite_and_debug(LogTargetHandle log,
                                     const char* format,
                                     va_list args
                                     DEBUG_ONLY(COMMA const char* file)
                                     DEBUG_ONLY(COMMA int line)) {
  DEBUG_ONLY(const char* debug_message;)

  {
    MutexLocker locker(_lock, Mutex::_no_safepoint_check_flag);
    vwrite_inner(log, format, args);
    DEBUG_ONLY(debug_message = os::strdup(_temp->base()));
  }

  // report error outside lock scope, since report_vm_error will call print_on_error
  DEBUG_ONLY(report_vm_error(file, line, debug_message);)
  DEBUG_ONLY(BREAKPOINT;)
}

void GCLogPrecious::print_on_error(outputStream* st) {
  st->print_cr("GC Precious Log:");

  if (_lines == nullptr) {
    st->print_cr("<Not initialized>\n");
    return;
  }

  if (!_lock->try_lock_without_rank_check()) {
    st->print_cr("<Skipped>\n");
    return;
  }

  if (_lines->size() == 0) {
    st->print_cr("<Empty>\n");
  } else {
    st->print_cr("%s", _lines->base());
  }

  _lock->unlock();
}