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#ifndef PurgeableVector_h
#define PurgeableVector_h
#include "platform/PlatformExport.h"
#include "wtf/Forward.h"
#include "wtf/Noncopyable.h"
#include "wtf/Vector.h"
namespace blink {
class WebDiscardableMemory;
} // namespace blink
namespace WebCore {
// A simple vector implementation that supports purgeable memory. The vector is
// already locked at construction and locking uses an internal counter which
// means that N calls to lock() must be followed by N+1 calls to unlock() to
// actually make the vector purgeable.
class PLATFORM_EXPORT PurgeableVector {
WTF_MAKE_NONCOPYABLE(PurgeableVector);
public:
enum PurgeableOption {
NotPurgeable,
Purgeable,
};
// Clients who know in advance that they will call unlock() should construct
// the instance with the Purgeable option so that the instance uses
// discardable memory from the start and unlock() doesn't cause a memcpy().
PurgeableVector(PurgeableOption = Purgeable);
~PurgeableVector();
// WARNING: This causes a memcpy() if the instance was constructed with the
// Purgeable hint or had its internal vector moved to discardable memory
// after a call to unlock().
void adopt(Vector<char>& other);
void append(const char* data, size_t length);
void grow(size_t);
void clear();
// The instance must be locked before calling this.
char* data();
size_t size() const;
// Returns whether the memory is still resident.
bool lock();
// WARNING: Calling unlock() on an instance that wasn't created with the
// Purgeable option does an extra memcpy().
void unlock();
bool isLocked() const;
// Note that this method should be used carefully since it may not use
// exponential growth internally. This means that repeated/invalid uses of
// it can result in O(N^2) append(). If you don't exactly know what you are
// doing then you should probably not call this method.
void reserveCapacity(size_t capacity);
private:
enum PurgeableAllocationStrategy {
UseExactCapacity,
UseExponentialGrowth,
};
// Copies data from the discardable buffer to the vector and clears the
// discardable buffer.
void moveDataFromDiscardableToVector();
void clearDiscardable();
bool reservePurgeableCapacity(size_t capacity, PurgeableAllocationStrategy);
size_t adjustPurgeableCapacity(size_t capacity) const;
// Vector used when the instance is constructed without the purgeability
// hint or when discardable memory allocation fails.
// Note that there can't be data both in |m_vector| and
// |m_discardable|, i.e. only one of them is used at a given time.
Vector<char> m_vector;
OwnPtr<blink::WebDiscardableMemory> m_discardable;
size_t m_discardableCapacity;
size_t m_discardableSize;
bool m_isPurgeable;
int m_locksCount;
};
} // namespace WebCore
#endif // PurgeableVector_h