monitor_pool.cc revision 2c26501d24d929abe096ecce44f91410290b33c0 
1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "monitor_pool.h"
18
19#include "base/logging.h"
20#include "base/mutex-inl.h"
21#include "thread-inl.h"
22#include "monitor.h"
23
24namespace art {
25
26namespace mirror {
27  class Object;
28}  // namespace mirror
29
30MonitorPool::MonitorPool()
31    : num_chunks_(0), capacity_(0), first_free_(nullptr) {
32  AllocateChunk();  // Get our first chunk.
33}
34
35// Assumes locks are held appropriately when necessary.
36// We do not need a lock in the constructor, but we need one when in CreateMonitorInPool.
37void MonitorPool::AllocateChunk() {
38  DCHECK(first_free_ == nullptr);
39
40  // Do we need to resize?
41  if (num_chunks_ == capacity_) {
42    if (capacity_ == 0U) {
43      // Initialization.
44      capacity_ = kInitialChunkStorage;
45      uintptr_t* new_backing = new uintptr_t[capacity_];
46      monitor_chunks_.StoreRelaxed(new_backing);
47    } else {
48      size_t new_capacity = 2 * capacity_;
49      uintptr_t* new_backing = new uintptr_t[new_capacity];
50      uintptr_t* old_backing = monitor_chunks_.LoadRelaxed();
51      memcpy(new_backing, old_backing, sizeof(uintptr_t) * capacity_);
52      monitor_chunks_.StoreRelaxed(new_backing);
53      capacity_ = new_capacity;
54      old_chunk_arrays_.push_back(old_backing);
55      VLOG(monitor) << "Resizing to capacity " << capacity_;
56    }
57  }
58
59  // Allocate the chunk.
60  void* chunk = malloc(kChunkSize);
61  // Check we allocated memory.
62  CHECK_NE(reinterpret_cast<uintptr_t>(nullptr), reinterpret_cast<uintptr_t>(chunk));
63  // Check it is aligned as we need it.
64  CHECK_EQ(0U, reinterpret_cast<uintptr_t>(chunk) % kMonitorAlignment);
65
66  // Add the chunk.
67  *(monitor_chunks_.LoadRelaxed() + num_chunks_) = reinterpret_cast<uintptr_t>(chunk);
68  num_chunks_++;
69
70  // Set up the free list
71  Monitor* last = reinterpret_cast<Monitor*>(reinterpret_cast<uintptr_t>(chunk) +
72                                             (kChunkCapacity - 1) * kAlignedMonitorSize);
73  last->next_free_ = nullptr;
74  // Eagerly compute id.
75  last->monitor_id_ = OffsetToMonitorId((num_chunks_ - 1) * kChunkSize +
76                                        (kChunkCapacity - 1) * kAlignedMonitorSize);
77  for (size_t i = 0; i < kChunkCapacity - 1; ++i) {
78    Monitor* before = reinterpret_cast<Monitor*>(reinterpret_cast<uintptr_t>(last) -
79                                                 kAlignedMonitorSize);
80    before->next_free_ = last;
81    // Derive monitor_id from last.
82    before->monitor_id_ = OffsetToMonitorId(MonitorIdToOffset(last->monitor_id_) -
83                                            kAlignedMonitorSize);
84
85    last = before;
86  }
87  DCHECK(last == reinterpret_cast<Monitor*>(chunk));
88  first_free_ = last;
89}
90
91Monitor* MonitorPool::CreateMonitorInPool(Thread* self, Thread* owner, mirror::Object* obj,
92                                          int32_t hash_code)
93    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
94  // We are gonna allocate, so acquire the writer lock.
95  MutexLock mu(self, *Locks::allocated_monitor_ids_lock_);
96
97  // Enough space, or need to resize?
98  if (first_free_ == nullptr) {
99    VLOG(monitor) << "Allocating a new chunk.";
100    AllocateChunk();
101  }
102
103  Monitor* mon_uninitialized = first_free_;
104  first_free_ = first_free_->next_free_;
105
106  // Pull out the id which was preinitialized.
107  MonitorId id = mon_uninitialized->monitor_id_;
108
109  // Initialize it.
110  Monitor* monitor = new(mon_uninitialized) Monitor(self, owner, obj, hash_code, id);
111
112  return monitor;
113}
114
115void MonitorPool::ReleaseMonitorToPool(Thread* self, Monitor* monitor) {
116  // Might be racy with allocation, so acquire lock.
117  MutexLock mu(self, *Locks::allocated_monitor_ids_lock_);
118
119  // Keep the monitor id. Don't trust it's not cleared.
120  MonitorId id = monitor->monitor_id_;
121
122  // Call the destructor.
123  // TODO: Exception safety?
124  monitor->~Monitor();
125
126  // Add to the head of the free list.
127  monitor->next_free_ = first_free_;
128  first_free_ = monitor;
129
130  // Rewrite monitor id.
131  monitor->monitor_id_ = id;
132}
133
134void MonitorPool::ReleaseMonitorsToPool(Thread* self, std::list<Monitor*>* monitors) {
135  for (Monitor* mon : *monitors) {
136    ReleaseMonitorToPool(self, mon);
137  }
138}
139
140}  // namespace art
141