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// Copyright 2012 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include <string.h>
#include "v8.h"
#include "zone-inl.h"
namespace v8 {
namespace internal {
// Segments represent chunks of memory: They have starting address
// (encoded in the this pointer) and a size in bytes. Segments are
// chained together forming a LIFO structure with the newest segment
// available as segment_head_. Segments are allocated using malloc()
// and de-allocated using free().
class Segment {
public:
void Initialize(Segment* next, int size) {
next_ = next;
size_ = size;
}
Segment* next() const { return next_; }
void clear_next() { next_ = NULL; }
int size() const { return size_; }
int capacity() const { return size_ - sizeof(Segment); }
Address start() const { return address(sizeof(Segment)); }
Address end() const { return address(size_); }
private:
// Computes the address of the nth byte in this segment.
Address address(int n) const {
return Address(this) + n;
}
Segment* next_;
int size_;
};
Zone::Zone(Isolate* isolate)
: zone_excess_limit_(256 * MB),
segment_bytes_allocated_(0),
position_(0),
limit_(0),
scope_nesting_(0),
segment_head_(NULL),
isolate_(isolate) {
}
unsigned Zone::allocation_size_ = 0;
ZoneScope::~ZoneScope() {
if (ShouldDeleteOnExit()) zone_->DeleteAll();
zone_->scope_nesting_--;
}
// Creates a new segment, sets it size, and pushes it to the front
// of the segment chain. Returns the new segment.
Segment* Zone::NewSegment(int size) {
Segment* result = reinterpret_cast<Segment*>(Malloced::New(size));
adjust_segment_bytes_allocated(size);
if (result != NULL) {
result->Initialize(segment_head_, size);
segment_head_ = result;
}
return result;
}
// Deletes the given segment. Does not touch the segment chain.
void Zone::DeleteSegment(Segment* segment, int size) {
adjust_segment_bytes_allocated(-size);
Malloced::Delete(segment);
}
void Zone::DeleteAll() {
#ifdef DEBUG
// Constant byte value used for zapping dead memory in debug mode.
static const unsigned char kZapDeadByte = 0xcd;
#endif
// Find a segment with a suitable size to keep around.
Segment* keep = segment_head_;
while (keep != NULL && keep->size() > kMaximumKeptSegmentSize) {
keep = keep->next();
}
// Traverse the chained list of segments, zapping (in debug mode)
// and freeing every segment except the one we wish to keep.
Segment* current = segment_head_;
while (current != NULL) {
Segment* next = current->next();
if (current == keep) {
// Unlink the segment we wish to keep from the list.
current->clear_next();
} else {
int size = current->size();
#ifdef DEBUG
// Zap the entire current segment (including the header).
memset(current, kZapDeadByte, size);
#endif
DeleteSegment(current, size);
}
current = next;
}
// If we have found a segment we want to keep, we must recompute the
// variables 'position' and 'limit' to prepare for future allocate
// attempts. Otherwise, we must clear the position and limit to
// force a new segment to be allocated on demand.
if (keep != NULL) {
Address start = keep->start();
position_ = RoundUp(start, kAlignment);
limit_ = keep->end();
#ifdef DEBUG
// Zap the contents of the kept segment (but not the header).
memset(start, kZapDeadByte, keep->capacity());
#endif
} else {
position_ = limit_ = 0;
}
// Update the head segment to be the kept segment (if any).
segment_head_ = keep;
}
void Zone::DeleteKeptSegment() {
if (segment_head_ != NULL) {
DeleteSegment(segment_head_, segment_head_->size());
segment_head_ = NULL;
}
}
Address Zone::NewExpand(int size) {
// Make sure the requested size is already properly aligned and that
// there isn't enough room in the Zone to satisfy the request.
ASSERT(size == RoundDown(size, kAlignment));
ASSERT(size > limit_ - position_);
// Compute the new segment size. We use a 'high water mark'
// strategy, where we increase the segment size every time we expand
// except that we employ a maximum segment size when we delete. This
// is to avoid excessive malloc() and free() overhead.
Segment* head = segment_head_;
int old_size = (head == NULL) ? 0 : head->size();
static const int kSegmentOverhead = sizeof(Segment) + kAlignment;
int new_size_no_overhead = size + (old_size << 1);
int new_size = kSegmentOverhead + new_size_no_overhead;
// Guard against integer overflow.
if (new_size_no_overhead < size || new_size < kSegmentOverhead) {
V8::FatalProcessOutOfMemory("Zone");
return NULL;
}
if (new_size < kMinimumSegmentSize) {
new_size = kMinimumSegmentSize;
} else if (new_size > kMaximumSegmentSize) {
// Limit the size of new segments to avoid growing the segment size
// exponentially, thus putting pressure on contiguous virtual address space.
// All the while making sure to allocate a segment large enough to hold the
// requested size.
new_size = Max(kSegmentOverhead + size, kMaximumSegmentSize);
}
Segment* segment = NewSegment(new_size);
if (segment == NULL) {
V8::FatalProcessOutOfMemory("Zone");
return NULL;
}
// Recompute 'top' and 'limit' based on the new segment.
Address result = RoundUp(segment->start(), kAlignment);
position_ = result + size;
// Check for address overflow.
if (position_ < result) {
V8::FatalProcessOutOfMemory("Zone");
return NULL;
}
limit_ = segment->end();
ASSERT(position_ <= limit_);
return result;
}
} } // namespace v8::internal
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