1 #ifndef DALI_INTEGRATION_LOCKLESS_BUFFER_H
2 #define DALI_INTEGRATION_LOCKLESS_BUFFER_H
5 * Copyright (c) 2019 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.
22 #include <cstdint> // uint32_t, uint8_t
26 #include <dali/public-api/common/vector-wrapper.h>
27 #include <dali/public-api/common/dali-common.h>
36 * The LocklessBuffer class implements double buffering eligible for multi-(two) threaded use,
37 * where it's possible to read from one thread and write from another
38 * without requiring a mutex lock to avoid performance hit.
39 * It's intended to be used for reading bitmap data in render thread
40 * while still possible to write data in another thread.
42 * Ideally Write() and Read() calls should be alternating, otherwise written data might be thrown away.
44 * The buffers are swapped in the reading thread, just before reading begins.
45 * In case the other thread is writing at that moment, buffers are not swapped and previously available data is read.
46 * Similarly if Write() is called before a Read() has finished the previous write buffer is overwritten.
48 class DALI_CORE_API LocklessBuffer
54 * @param[in] size The size of buffers in bytes.
56 LocklessBuffer( uint32_t size );
64 * Write data to buffer.
65 * @param[in] src data source
66 * @param[in] size size of data in bytes
68 void Write( const uint8_t *src, uint32_t size );
71 * Try to swap buffers and read data.
72 * @note returned value only valid until Read() is called again or object is destroyed
73 * @return current read buffer contents
75 const uint8_t* Read();
78 * @return the buffer size in bytes
80 uint32_t GetSize() const;
84 * Atomically set state.
85 * We're always writing to one buffer and reading from the other.
86 * Write() sets WRITING bit when started and unsets it when finished.
90 R0W1 = 0, ///< Read from buffer 0 write to buffer 1
91 R1W0 = 1, ///< Read from buffer 1 write to buffer 0
92 WRITING = 2, ///< Currently writing to buffer
93 UPDATED = 4, ///< Swapping buffer required; there is new data available
94 WRITE_BUFFER_MASK = 1, ///< indicates which buffer to write to
95 WRITING_MASK = 2, ///< indicates whether currently writing
96 UPDATED_MASK = 4 ///< indicates whether new data is available
100 LocklessBuffer(); ///< undefined default constructor, need to give size on construction
101 LocklessBuffer( const LocklessBuffer& ); ///< undefined copy constructor
102 LocklessBuffer& operator=( const LocklessBuffer& ); ///< undefined assignment operator
105 uint8_t* mBuffer[2]; ///< bitmap buffers
106 BufferState volatile mState; ///< readbuffer number and whether we're currently writing into writebuffer or not
107 uint32_t mSize; ///< size of buffers
114 #endif // DALI_INTEGRATION_LOCKLESS_BUFFER_H