parsebyparts.cpp 5.03 KB
Newer Older
Milo Yip's avatar
Milo Yip committed
1 2 3
// Example of parsing JSON to document by parts.

// Using C++11 threads
4 5
// Temporarily disable for clang (older version) due to incompatibility with libstdc++
#if (__cplusplus >= 201103L || (defined(_MSC_VER) && _MSC_VER >= 1700)) && !defined(__clang__)
Milo Yip's avatar
Milo Yip committed
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

#include "rapidjson/document.h"
#include "rapidjson/error/en.h"
#include "rapidjson/writer.h"
#include "rapidjson/ostreamwrapper.h"
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <thread>

using namespace rapidjson;

template<unsigned parseFlags = kParseDefaultFlags>
class AsyncDocumentParser {
public:
21 22 23
    AsyncDocumentParser(Document& d)
        : stream_(*this)
        , d_(d)
24
        , parseThread_()
25 26 27 28
        , mutex_()
        , notEmpty_()
        , finish_()
        , completed_()
29 30 31 32
    {
        // Create and execute thread after all member variables are initialized.
        parseThread_ = std::thread(&AsyncDocumentParser::Parse, this);
    }
Milo Yip's avatar
Milo Yip committed
33 34 35 36 37 38 39 40 41

    ~AsyncDocumentParser() {
        if (!parseThread_.joinable())
            return;

        {        
            std::unique_lock<std::mutex> lock(mutex_);

            // Wait until the buffer is read up (or parsing is completed)
42
            while (!stream_.Empty() && !completed_)
Milo Yip's avatar
Milo Yip committed
43 44 45 46
                finish_.wait(lock);

            // Automatically append '\0' as the terminator in the stream.
            static const char terminator[] = "";
47 48
            stream_.src_ = terminator;
            stream_.end_ = terminator + 1;
Milo Yip's avatar
Milo Yip committed
49 50 51 52 53 54 55 56 57 58
            notEmpty_.notify_one(); // unblock the AsyncStringStream
        }

        parseThread_.join();
    }

    void ParsePart(const char* buffer, size_t length) {
        std::unique_lock<std::mutex> lock(mutex_);
        
        // Wait until the buffer is read up (or parsing is completed)
59
        while (!stream_.Empty() && !completed_)
Milo Yip's avatar
Milo Yip committed
60 61 62 63 64 65 66
            finish_.wait(lock);

        // Stop further parsing if the parsing process is completed.
        if (completed_)
            return;

        // Set the buffer to stream and unblock the AsyncStringStream
67 68
        stream_.src_ = buffer;
        stream_.end_ = buffer + length;
Milo Yip's avatar
Milo Yip committed
69 70 71 72 73
        notEmpty_.notify_one();
    }

private:
    void Parse() {
74
        d_.ParseStream<parseFlags>(stream_);
Milo Yip's avatar
Milo Yip committed
75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129

        // The stream may not be fully read, notify finish anyway to unblock ParsePart()
        std::unique_lock<std::mutex> lock(mutex_);
        completed_ = true;      // Parsing process is completed
        finish_.notify_one();   // Unblock ParsePart() or destructor if they are waiting.
    }

    struct AsyncStringStream {
        typedef char Ch;

        AsyncStringStream(AsyncDocumentParser& parser) : parser_(parser), src_(), end_(), count_() {}

        char Peek() const {
            std::unique_lock<std::mutex> lock(parser_.mutex_);

            // If nothing in stream, block to wait.
            while (Empty())
                parser_.notEmpty_.wait(lock);

            return *src_;
        }

        char Take() {
            std::unique_lock<std::mutex> lock(parser_.mutex_);

            // If nothing in stream, block to wait.
            while (Empty())
                parser_.notEmpty_.wait(lock);

            count_++;
            char c = *src_++;

            // If all stream is read up, notify that the stream is finish.
            if (Empty())
                parser_.finish_.notify_one();

            return c;
        }

        size_t Tell() const { return count_; }

        // Not implemented
        char* PutBegin() { return 0; }
        void Put(char) {}
        void Flush() {}
        size_t PutEnd(char*) { return 0; }

        bool Empty() const { return src_ == end_; }

        AsyncDocumentParser& parser_;
        const char* src_;     //!< Current read position.
        const char* end_;     //!< End of buffer
        size_t count_;        //!< Number of characters taken so far.
    };

130
    AsyncStringStream stream_;
Milo Yip's avatar
Milo Yip committed
131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176
    Document& d_;
    std::thread parseThread_;
    std::mutex mutex_;
    std::condition_variable notEmpty_;
    std::condition_variable finish_;
    bool completed_;
};

int main() {
    Document d;

    {
        AsyncDocumentParser<> parser(d);

        const char json1[] = " { \"hello\" : \"world\", \"t\" : tr";
        //const char json1[] = " { \"hello\" : \"world\", \"t\" : trX"; // Fot test parsing error
        const char json2[] = "ue, \"f\" : false, \"n\": null, \"i\":123, \"pi\": 3.14";
        const char json3[] = "16, \"a\":[1, 2, 3, 4] } ";

        parser.ParsePart(json1, sizeof(json1) - 1);
        parser.ParsePart(json2, sizeof(json2) - 1);
        parser.ParsePart(json3, sizeof(json3) - 1);
    }

    if (d.HasParseError()) {
        std::cout << "Error at offset " << d.GetErrorOffset() << ": " << GetParseError_En(d.GetParseError()) << std::endl;
        return EXIT_FAILURE;
    }
    
    // Stringify the JSON to cout
    OStreamWrapper os(std::cout);
    Writer<OStreamWrapper> writer(os);
    d.Accept(writer);
    std::cout << std::endl;

    return EXIT_SUCCESS;
}

#else // Not supporting C++11 

#include <iostream>
int main() {
    std::cout << "This example requires C++11 compiler" << std::endl;
}

#endif