1 #ifndef __DALI_INTEGRATION_LOCKLESS_BUFFER_H__
2 #define __DALI_INTEGRATION_LOCKLESS_BUFFER_H__
5 * Copyright (c) 2018 Samsung Electronics Co., Ltd.
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
11 * http://www.apache.org/licenses/LICENSE-2.0
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
25 #include <dali/public-api/common/vector-wrapper.h>
26 #include <dali/public-api/common/dali-common.h>
37 * The LocklessBuffer class implements double buffering eligible for multi-(two) threaded use,
38 * where it's possible to read from one thread and write from another
39 * without requiring a mutex lock to avoid performance hit.
40 * It's intended to be used for reading bitmap data in render thread
41 * while still possible to write data in another thread.
43 * Ideally Write() and Read() calls should be alternating, otherwise written data might be thrown away.
45 * The buffers are swapped in the reading thread, just before reading begins.
46 * In case the other thread is writing at that moment, buffers are not swapped and previously available data is read.
47 * Similarly if Write() is called before a Read() has finished the previous write buffer is overwritten.
49 class DALI_CORE_API LocklessBuffer
55 * @param[in] size The size of buffers in bytes.
57 LocklessBuffer( size_t size );
65 * Write data to buffer.
66 * @param[in] src data source
67 * @param[in] size size of data in bytes
69 void Write( const unsigned char *src, size_t size );
72 * Try to swap buffers and read data.
73 * @note returned value only valid until Read() is called again or object is destroyed
74 * @return current read buffer contents
76 const unsigned char* Read();
79 * @return the buffer size in bytes
81 unsigned int GetSize() const;
85 * Atomically set state.
86 * We're always writing to one buffer and reading from the other.
87 * Write() sets WRITING bit when started and unsets it when finished.
91 R0W1 = 0, ///< Read from buffer 0 write to buffer 1
92 R1W0 = 1, ///< Read from buffer 1 write to buffer 0
93 WRITING = 2, ///< Currently writing to buffer
94 UPDATED = 4, ///< Swapping buffer required; there is new data available
95 WRITE_BUFFER_MASK = 1, ///< indicates which buffer to write to
96 WRITING_MASK = 2, ///< indicates whether currently writing
97 UPDATED_MASK = 4 ///< indicates whether new data is available
101 LocklessBuffer(); ///< undefined default constructor, need to give size on construction
102 LocklessBuffer( const LocklessBuffer& ); ///< undefined copy constructor
103 LocklessBuffer& operator=( const LocklessBuffer& ); ///< undefined assignment operator
106 unsigned char* mBuffer[2]; ///< bitmap buffers
107 volatile std::__atomic_base<BufferState> mState; ///< readbuffer number and whether we're currently writing into writebuffer or not
108 size_t mSize; ///< size of buffers
115 #endif // __DALI_INTEGRATION_LOCKLESS_H__