1 /**

     2  * Relational pipes

     3  * Copyright © 2021 František Kučera (Frantovo.cz, GlobalCode.info)

     4  *

     5  * This program is free software: you can redistribute it and/or modify

     6  * it under the terms of the GNU General Public License as published by

     7  * the Free Software Foundation, version 3 of the License.

     8  *

     9  * This program is distributed in the hope that it will be useful,

    10  * but WITHOUT ANY WARRANTY; without even the implied warranty of

    11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

    12  * GNU General Public License for more details.

    13  *

    14  * You should have received a copy of the GNU General Public License

    15  * along with this program. If not, see <http://www.gnu.org/licenses/>.

    16  */

    17 #pragma once

    18 

    19 #include <string>

    20 #include <exception>

    21 #include <cstring>

    22 

    23 #include "AbstractParser.h"

    24 

    25 namespace relpipe {

    26 namespace in {

    27 namespace asn1 {

    28 namespace lib {

    29 

    30 class TransactionalBuffer {

    31 private:

    32 	char* buffer;

    33 	size_t bufferSize;

    34 	bool hasData = false;

    35 	size_t writePosition = 0;

    36 	// size_t writePositionCommited = 0; // TODO: transactions also on the writing side?

    37 	size_t readPosition = 0;

    38 	size_t readPositionCommited = 0;

    39 

    40 	size_t availableForReading() {

    41 		if (readPosition < writePosition) return writePosition - readPosition;

    42 		else if (readPosition > writePosition) return bufferSize - readPosition + writePosition;

    43 		else if (hasData) return bufferSize;

    44 		else return 0;

    45 	}

    46 

    47 	size_t availableForWriting() {

    48 		if (readPositionCommited < writePosition) return bufferSize - writePosition + readPositionCommited;

    49 		else if (readPositionCommited > writePosition) return readPositionCommited - writePosition;

    50 		else if (hasData) return 0;

    51 		else return bufferSize;

    52 	}

    53 

    54 public:

    55 

    56 		/**

    57 	 * Is thrown from read() and peak() methods if there are not enough data.

    58 	 * Interrupts current update() cycle and causes rollback.

    59 	 */

    60 	class ReadBufferUnderflowException {

    61 		// TODO: common super-class for exceptions, hidden implementation

    62 	};

    63 

    64 	/**

    65 	 * Is thrown from write() method of the buffer when there is not enough space.

    66 	 * Interrupts whole process.

    67 	 */

    68 	class WriteBufferOverflowException {

    69 	};

    70 

    71 	TransactionalBuffer(size_t initialSize = 4096) : bufferSize(initialSize) {

    72 		// TODO: initial size + resize + hard upper limit

    73 		buffer = (char*) malloc(bufferSize);

    74 	}

    75 

    76 	virtual ~TransactionalBuffer() {

    77 		free(buffer);

    78 	}

    79 

    80 	void write(const char* inputBuffer, const size_t length) {

    81 		if (length == 0) return;

    82 		if (length > availableForWriting()) throw WriteBufferOverflowException(); // TODO: optional resize

    83 

    84 		hasData = true;

    85 

    86 		const size_t a = std::min(length, bufferSize - writePosition);

    87 		const size_t b = length - a;

    88 

    89 		// TODO: map buffer twice in the memory in order to create a continuous area and avoid the second memcpy()?

    90 		memcpy(buffer + writePosition, inputBuffer, a);

    91 		memcpy(buffer, inputBuffer + a, b);

    92 

    93 		writePosition = (writePosition + length) % bufferSize;

    94 	}

    95 

    96 	void read(char* outputBuffer, const size_t length) {

    97 		if (length == 0) return;

    98 

    99 		peek(outputBuffer, length);

   100 		readPosition = (readPosition + length) % bufferSize;

   101 		hasData = readPosition != writePosition;

   102 	}

   103 

   104 	void peek(char* outputBuffer, const size_t length) {

   105 		if (length == 0) return;

   106 		if (length > availableForReading()) throw ReadBufferUnderflowException();

   107 

   108 		const size_t a = std::min(length, bufferSize - readPosition);

   109 		const size_t b = length - a;

   110 

   111 		memcpy(outputBuffer, buffer + readPosition, a);

   112 		memcpy(outputBuffer + a, buffer, b);

   113 	}

   114 

   115 	void commitRead() {

   116 		readPositionCommited = readPosition;

   117 	}

   118 

   119 	void rollbackRead() {

   120 		readPosition = readPositionCommited;

   121 	}

   122 };

   123 

   124 

   125 }

   126 }

   127 }

   128 }