1// Copyright 2012 the V8 project authors. All rights reserved.
2// Redistribution and use in source and binary forms, with or without
3// modification, are permitted provided that the following conditions are
4// met:
5//
6//     * Redistributions of source code must retain the above copyright
7//       notice, this list of conditions and the following disclaimer.
8//     * Redistributions in binary form must reproduce the above
9//       copyright notice, this list of conditions and the following
10//       disclaimer in the documentation and/or other materials provided
11//       with the distribution.
12//     * Neither the name of Google Inc. nor the names of its
13//       contributors may be used to endorse or promote products derived
14//       from this software without specific prior written permission.
15//
16// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
28#include <string.h>
29
30#include "v8.h"
31#include "zone-inl.h"
32
33namespace v8 {
34namespace internal {
35
36
37// Segments represent chunks of memory: They have starting address
38// (encoded in the this pointer) and a size in bytes. Segments are
39// chained together forming a LIFO structure with the newest segment
40// available as segment_head_. Segments are allocated using malloc()
41// and de-allocated using free().
42
43class Segment {
44 public:
45  void Initialize(Segment* next, int size) {
46    next_ = next;
47    size_ = size;
48  }
49
50  Segment* next() const { return next_; }
51  void clear_next() { next_ = NULL; }
52
53  int size() const { return size_; }
54  int capacity() const { return size_ - sizeof(Segment); }
55
56  Address start() const { return address(sizeof(Segment)); }
57  Address end() const { return address(size_); }
58
59 private:
60  // Computes the address of the nth byte in this segment.
61  Address address(int n) const {
62    return Address(this) + n;
63  }
64
65  Segment* next_;
66  int size_;
67};
68
69
70Zone::Zone()
71    : zone_excess_limit_(256 * MB),
72      segment_bytes_allocated_(0),
73      position_(0),
74      limit_(0),
75      scope_nesting_(0),
76      segment_head_(NULL) {
77}
78unsigned Zone::allocation_size_ = 0;
79
80ZoneScope::~ZoneScope() {
81  ASSERT_EQ(Isolate::Current(), isolate_);
82  if (ShouldDeleteOnExit()) isolate_->zone()->DeleteAll();
83  isolate_->zone()->scope_nesting_--;
84}
85
86
87// Creates a new segment, sets it size, and pushes it to the front
88// of the segment chain. Returns the new segment.
89Segment* Zone::NewSegment(int size) {
90  Segment* result = reinterpret_cast<Segment*>(Malloced::New(size));
91  adjust_segment_bytes_allocated(size);
92  if (result != NULL) {
93    result->Initialize(segment_head_, size);
94    segment_head_ = result;
95  }
96  return result;
97}
98
99
100// Deletes the given segment. Does not touch the segment chain.
101void Zone::DeleteSegment(Segment* segment, int size) {
102  adjust_segment_bytes_allocated(-size);
103  Malloced::Delete(segment);
104}
105
106
107void Zone::DeleteAll() {
108#ifdef DEBUG
109  // Constant byte value used for zapping dead memory in debug mode.
110  static const unsigned char kZapDeadByte = 0xcd;
111#endif
112
113  // Find a segment with a suitable size to keep around.
114  Segment* keep = segment_head_;
115  while (keep != NULL && keep->size() > kMaximumKeptSegmentSize) {
116    keep = keep->next();
117  }
118
119  // Traverse the chained list of segments, zapping (in debug mode)
120  // and freeing every segment except the one we wish to keep.
121  Segment* current = segment_head_;
122  while (current != NULL) {
123    Segment* next = current->next();
124    if (current == keep) {
125      // Unlink the segment we wish to keep from the list.
126      current->clear_next();
127    } else {
128      int size = current->size();
129#ifdef DEBUG
130      // Zap the entire current segment (including the header).
131      memset(current, kZapDeadByte, size);
132#endif
133      DeleteSegment(current, size);
134    }
135    current = next;
136  }
137
138  // If we have found a segment we want to keep, we must recompute the
139  // variables 'position' and 'limit' to prepare for future allocate
140  // attempts. Otherwise, we must clear the position and limit to
141  // force a new segment to be allocated on demand.
142  if (keep != NULL) {
143    Address start = keep->start();
144    position_ = RoundUp(start, kAlignment);
145    limit_ = keep->end();
146#ifdef DEBUG
147    // Zap the contents of the kept segment (but not the header).
148    memset(start, kZapDeadByte, keep->capacity());
149#endif
150  } else {
151    position_ = limit_ = 0;
152  }
153
154  // Update the head segment to be the kept segment (if any).
155  segment_head_ = keep;
156}
157
158
159void Zone::DeleteKeptSegment() {
160  if (segment_head_ != NULL) {
161    DeleteSegment(segment_head_, segment_head_->size());
162    segment_head_ = NULL;
163  }
164}
165
166
167Address Zone::NewExpand(int size) {
168  // Make sure the requested size is already properly aligned and that
169  // there isn't enough room in the Zone to satisfy the request.
170  ASSERT(size == RoundDown(size, kAlignment));
171  ASSERT(size > limit_ - position_);
172
173  // Compute the new segment size. We use a 'high water mark'
174  // strategy, where we increase the segment size every time we expand
175  // except that we employ a maximum segment size when we delete. This
176  // is to avoid excessive malloc() and free() overhead.
177  Segment* head = segment_head_;
178  int old_size = (head == NULL) ? 0 : head->size();
179  static const int kSegmentOverhead = sizeof(Segment) + kAlignment;
180  int new_size_no_overhead = size + (old_size << 1);
181  int new_size = kSegmentOverhead + new_size_no_overhead;
182  // Guard against integer overflow.
183  if (new_size_no_overhead < size || new_size < kSegmentOverhead) {
184    V8::FatalProcessOutOfMemory("Zone");
185    return NULL;
186  }
187  if (new_size < kMinimumSegmentSize) {
188    new_size = kMinimumSegmentSize;
189  } else if (new_size > kMaximumSegmentSize) {
190    // Limit the size of new segments to avoid growing the segment size
191    // exponentially, thus putting pressure on contiguous virtual address space.
192    // All the while making sure to allocate a segment large enough to hold the
193    // requested size.
194    new_size = Max(kSegmentOverhead + size, kMaximumSegmentSize);
195  }
196  Segment* segment = NewSegment(new_size);
197  if (segment == NULL) {
198    V8::FatalProcessOutOfMemory("Zone");
199    return NULL;
200  }
201
202  // Recompute 'top' and 'limit' based on the new segment.
203  Address result = RoundUp(segment->start(), kAlignment);
204  position_ = result + size;
205  // Check for address overflow.
206  if (position_ < result) {
207    V8::FatalProcessOutOfMemory("Zone");
208    return NULL;
209  }
210  limit_ = segment->end();
211  ASSERT(position_ <= limit_);
212  return result;
213}
214
215
216} }  // namespace v8::internal
217