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/** |
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* This file is part of the CernVM File System. |
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*/ |
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#ifndef CVMFS_RING_BUFFER_H_ |
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#define CVMFS_RING_BUFFER_H_ |
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#include <cstddef> |
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#include "util/single_copy.h" |
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/** |
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* A ring buffer that allows appending objects to the front and removing |
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* objects from the back. In the memory area, we prepend the object data with |
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* the size of the object. |
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*/ |
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class RingBuffer : SingleCopy { |
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public: |
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/** |
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* The offset in buffer_ |
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*/ |
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typedef size_t ObjectHandle_t; |
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static const ObjectHandle_t kInvalidObjectHandle; |
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explicit RingBuffer(size_t total_size); |
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~RingBuffer(); |
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/** |
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* Returns kInvalidObjectHandle if there is not enough space to insert the |
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* object. |
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*/ |
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ObjectHandle_t PushFront(const void *obj, size_t size); |
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/** |
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* Returns the handle of the remove object or kInvalidObjectHandle if the |
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* ring buffer is empty |
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*/ |
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ObjectHandle_t RemoveBack(); |
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/** |
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* The passed object handle must be valid |
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*/ |
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size_t GetObjectSize(ObjectHandle_t handle) const; |
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/** |
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* Note that we cannot just return a pointer because an object may be |
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* split between the end and the beginning of the backing memory area |
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*/ |
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void CopyObject(ObjectHandle_t handle, void *to) const; |
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/** |
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* Copies a sub range of the object |
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*/ |
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void CopySlice(ObjectHandle_t handle, size_t size, size_t offset, |
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void *to) const; |
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// All objects are prepended by a size tag, so we can store objects only |
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// up to the available space minus the size of the size tag |
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size_t GetMaxObjectSize() const { return total_size_ - sizeof(size_t); } |
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bool HasSpaceFor(size_t size) const { |
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return free_space_ >= size + sizeof(size_t); |
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} |
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size_t free_space() const { return free_space_; } |
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private: |
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/** |
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* Writes data into the ring buffer at front_, taking care of a potential |
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* buffer wrap. Assumes that the buffer has enough space. |
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*/ |
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void Put(const void *data, size_t size); |
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/** |
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* Copies data from the buffer to the memory area "to". The memory area |
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* has to be big enough. Takes care of a potential buffer wrap. |
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*/ |
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void Get(size_t from, size_t size, void *to) const; |
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/** |
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* Moves the back_ pointer forward, taking care of potential buffer wraps |
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*/ |
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void Shrink(size_t by); |
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/** |
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* Size in bytes of the memory area backing the ring buffer |
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*/ |
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const size_t total_size_; |
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/** |
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* Size in bytes of the unused space in the buffer |
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*/ |
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size_t free_space_; |
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/** |
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* Pointer to the front of the memory buffer, in [0, size_ - 1] |
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*/ |
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size_t front_; |
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/** |
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* Pointer to the back of the memory buffer, in [0, size_ - 1] |
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*/ |
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size_t back_; |
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/** |
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* The memory area backing the ring buffer |
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*/ |
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unsigned char *buffer_; |
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}; // class RingBuffer |
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#endif // CVMFS_RING_H_ |
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