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Java example source code file (stubs.cpp)

This example Java source code file (stubs.cpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

bufferblob, codecache, codeentryalignment, codestrings, mutexlockerex, null, stub, stubqueue\:\:queues_do, stubqueue\:\:register_queue, stubqueue\:\:remove_all, stubqueue\:\:remove_first, stubqueue\:\:request, stubqueue\:\:stub_containing, stubqueuelimit

The stubs.cpp Java example source code

/*
 * Copyright (c) 1997, 2013, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "code/codeBlob.hpp"
#include "code/stubs.hpp"
#include "memory/allocation.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/mutexLocker.hpp"


// Implementation of StubQueue
//
// Standard wrap-around queue implementation; the queue dimensions
// are specified by the _queue_begin & _queue_end indices. The queue
// can be in two states (transparent to the outside):
//
// a) contiguous state: all queue entries in one block (or empty)
//
// Queue: |...|XXXXXXX|...............|
//        ^0  ^begin  ^end            ^size = limit
//            |_______|
//            one block
//
// b) non-contiguous state: queue entries in two blocks
//
// Queue: |XXX|.......|XXXXXXX|.......|
//        ^0  ^end    ^begin  ^limit  ^size
//        |___|       |_______|
//         1st block  2nd block
//
// In the non-contiguous state, the wrap-around point is
// indicated via the _buffer_limit index since the last
// queue entry may not fill up the queue completely in
// which case we need to know where the 2nd block's end
// is to do the proper wrap-around. When removing the
// last entry of the 2nd block, _buffer_limit is reset
// to _buffer_size.
//
// CAUTION: DO NOT MESS WITH THIS CODE IF YOU CANNOT PROVE
// ITS CORRECTNESS! THIS CODE IS MORE SUBTLE THAN IT LOOKS!


StubQueue::StubQueue(StubInterface* stub_interface, int buffer_size,
                     Mutex* lock, const char* name) : _mutex(lock) {
  intptr_t size = round_to(buffer_size, 2*BytesPerWord);
  BufferBlob* blob = BufferBlob::create(name, size);
  if( blob == NULL) {
    vm_exit_out_of_memory(size, OOM_MALLOC_ERROR, err_msg("CodeCache: no room for %s", name));
  }
  _stub_interface  = stub_interface;
  _buffer_size     = blob->content_size();
  _buffer_limit    = blob->content_size();
  _stub_buffer     = blob->content_begin();
  _queue_begin     = 0;
  _queue_end       = 0;
  _number_of_stubs = 0;
  register_queue(this);
}


StubQueue::~StubQueue() {
  // Note: Currently StubQueues are never destroyed so nothing needs to be done here.
  //       If we want to implement the destructor, we need to release the BufferBlob
  //       allocated in the constructor (i.e., we need to keep it around or look it
  //       up via CodeCache::find_blob(...).
  Unimplemented();
}


Stub* StubQueue::stub_containing(address pc) const {
  if (contains(pc)) {
    for (Stub* s = first(); s != NULL; s = next(s)) {
      if (stub_contains(s, pc)) return s;
    }
  }
  return NULL;
}


Stub* StubQueue::request_committed(int code_size) {
  Stub* s = request(code_size);
  CodeStrings strings;
  if (s != NULL) commit(code_size, strings);
  return s;
}


Stub* StubQueue::request(int requested_code_size) {
  assert(requested_code_size > 0, "requested_code_size must be > 0");
  if (_mutex != NULL) _mutex->lock();
  Stub* s = current_stub();
  int requested_size = round_to(stub_code_size_to_size(requested_code_size), CodeEntryAlignment);
  if (requested_size <= available_space()) {
    if (is_contiguous()) {
      // Queue: |...|XXXXXXX|.............|
      //        ^0  ^begin  ^end          ^size = limit
      assert(_buffer_limit == _buffer_size, "buffer must be fully usable");
      if (_queue_end + requested_size <= _buffer_size) {
        // code fits in at the end => nothing to do
        CodeStrings strings;
        stub_initialize(s, requested_size, strings);
        return s;
      } else {
        // stub doesn't fit in at the queue end
        // => reduce buffer limit & wrap around
        assert(!is_empty(), "just checkin'");
        _buffer_limit = _queue_end;
        _queue_end = 0;
      }
    }
  }
  if (requested_size <= available_space()) {
    assert(!is_contiguous(), "just checkin'");
    assert(_buffer_limit <= _buffer_size, "queue invariant broken");
    // Queue: |XXX|.......|XXXXXXX|.......|
    //        ^0  ^end    ^begin  ^limit  ^size
    s = current_stub();
    CodeStrings strings;
    stub_initialize(s, requested_size, strings);
    return s;
  }
  // Not enough space left
  if (_mutex != NULL) _mutex->unlock();
  return NULL;
}


void StubQueue::commit(int committed_code_size, CodeStrings& strings) {
  assert(committed_code_size > 0, "committed_code_size must be > 0");
  int committed_size = round_to(stub_code_size_to_size(committed_code_size), CodeEntryAlignment);
  Stub* s = current_stub();
  assert(committed_size <= stub_size(s), "committed size must not exceed requested size");
  stub_initialize(s, committed_size, strings);
  _queue_end += committed_size;
  _number_of_stubs++;
  if (_mutex != NULL) _mutex->unlock();
  debug_only(stub_verify(s);)
}


void StubQueue::remove_first() {
  if (number_of_stubs() == 0) return;
  Stub* s = first();
  debug_only(stub_verify(s);)
  stub_finalize(s);
  _queue_begin += stub_size(s);
  assert(_queue_begin <= _buffer_limit, "sanity check");
  if (_queue_begin == _queue_end) {
    // buffer empty
    // => reset queue indices
    _queue_begin  = 0;
    _queue_end    = 0;
    _buffer_limit = _buffer_size;
  } else if (_queue_begin == _buffer_limit) {
    // buffer limit reached
    // => reset buffer limit & wrap around
    _buffer_limit = _buffer_size;
    _queue_begin = 0;
  }
  _number_of_stubs--;
}


void StubQueue::remove_first(int n) {
  int i = MIN2(n, number_of_stubs());
  while (i-- > 0) remove_first();
}


void StubQueue::remove_all(){
  debug_only(verify();)
  remove_first(number_of_stubs());
  assert(number_of_stubs() == 0, "sanity check");
}


enum { StubQueueLimit = 10 };  // there are only a few in the world
static StubQueue* registered_stub_queues[StubQueueLimit];

void StubQueue::register_queue(StubQueue* sq) {
  for (int i = 0; i < StubQueueLimit; i++) {
    if (registered_stub_queues[i] == NULL) {
      registered_stub_queues[i] = sq;
      return;
    }
  }
  ShouldNotReachHere();
}


void StubQueue::queues_do(void f(StubQueue* sq)) {
  for (int i = 0; i < StubQueueLimit; i++) {
    if (registered_stub_queues[i] != NULL) {
      f(registered_stub_queues[i]);
    }
  }
}


void StubQueue::stubs_do(void f(Stub* s)) {
  debug_only(verify();)
  MutexLockerEx lock(_mutex);
  for (Stub* s = first(); s != NULL; s = next(s)) f(s);
}


void StubQueue::verify() {
  // verify only if initialized
  if (_stub_buffer == NULL) return;
  MutexLockerEx lock(_mutex);
  // verify index boundaries
  guarantee(0 <= _buffer_size, "buffer size must be positive");
  guarantee(0 <= _buffer_limit && _buffer_limit <= _buffer_size , "_buffer_limit out of bounds");
  guarantee(0 <= _queue_begin  && _queue_begin  <  _buffer_limit, "_queue_begin out of bounds");
  guarantee(0 <= _queue_end    && _queue_end    <= _buffer_limit, "_queue_end   out of bounds");
  // verify alignment
  guarantee(_buffer_size  % CodeEntryAlignment == 0, "_buffer_size  not aligned");
  guarantee(_buffer_limit % CodeEntryAlignment == 0, "_buffer_limit not aligned");
  guarantee(_queue_begin  % CodeEntryAlignment == 0, "_queue_begin  not aligned");
  guarantee(_queue_end    % CodeEntryAlignment == 0, "_queue_end    not aligned");
  // verify buffer limit/size relationship
  if (is_contiguous()) {
    guarantee(_buffer_limit == _buffer_size, "_buffer_limit must equal _buffer_size");
  }
  // verify contents
  int n = 0;
  for (Stub* s = first(); s != NULL; s = next(s)) {
    stub_verify(s);
    n++;
  }
  guarantee(n == number_of_stubs(), "number of stubs inconsistent");
  guarantee(_queue_begin != _queue_end || n == 0, "buffer indices must be the same");
}


void StubQueue::print() {
  MutexLockerEx lock(_mutex);
  for (Stub* s = first(); s != NULL; s = next(s)) {
    stub_print(s);
  }
}

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