C++ studying of parallel + multithreading (c++11) following https://www.youtube.com/watch?v=_z-RS0rXg9s with some differences. Compile with "g++ -std=c++11 SimpleDownloader.cpp -lpthread -lcurl"

SimpleDownloaders_future.cpp

/** Downloader app following https://www.youtube.com/watch?v=_z-RS0rXg9s but 
 * use libcurl (C API) with some adjusted API usage. 
 *
 * Compile with
 * g++ -std=c++11 -DNO_PROXY SimpleDownloader.cpp -lpthread -lcurl
 * */

#include <iostream>
#include <fstream>
#include <string>
#include <curl/curl.h>
#include <cstdlib>
#include <cstring>
#include <thread>
#include <vector>
#include <mutex>
#include <future>

struct MemoryHolder
{
    char *mem;
    size_t size;
    std::string filename; 
    unsigned line;
};

static const std::string ROOT_URL = "http://iki.fi/bisqwit/ctu85/";

static unsigned ln = 1;
static std::string Color(int n, const std::string& s)
{
    return "\33[" + std::to_string(n) + 'm' + s + "\33[m";
}
static std::string Line(int l)
{
    int m = l - ln;
    ln = l;

    return "\r" + (m < 0 ? "\33[" + std::to_string(-m) + 'A': std::string(m, '\n'));
}
static std::string ClearLine(int l)
{
    return "\33[2K";
}

static std::mutex PrintLock;

static int ProgressFunction(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow)
{
    // scope mutex lock
    std::lock_guard<std::mutex> lock(PrintLock);

    MemoryHolder mHolder = *(MemoryHolder*)clientp;
    std::cout << Line(mHolder.line) << ClearLine(mHolder.line) << Color(93, mHolder.filename + ": ") << dlnow << " of " << dltotal
    << " bytes received (" << int(dltotal ? dlnow * 100.0/dltotal : 0) << "%)" << std::flush;

    return 0;    
}

static size_t WriteFunction(char *contents, std::size_t size, std::size_t nmemb, void *userp)
{
    size_t realsize = size * nmemb;
    MemoryHolder *mholder = (MemoryHolder*)userp;

    // memory chunk needs to be allocated first
    // this will ensure it will before we call realloc()
    if (mholder->mem == nullptr)
        mholder->mem = (char*)std::malloc(1);

    char *ptr = (char*)std::realloc(mholder->mem, mholder->size + realsize + 1);
    if (!ptr)
    {
        // out of memory
        std::cout << Line(mholder->line) << ClearLine(mholder->line) << Color(31, "Not enough memory") << std::flush;
        // return number of bytes that handled which we didn't handle any
        return 0;
    }

    // set new memory location that has been re-allocated
    mholder->mem = ptr;
    std::memcpy(&(mholder->mem[mholder->size]), contents, realsize);
    mholder->size += realsize;
    // set null-terminated character
    mholder->mem[mholder->size] = 0;

    return realsize;
}

static std::size_t Download(const std::string& url, const std::string& filename, const unsigned line)
{
    CURL *curl = curl_easy_init();
    if (!curl)
    {
        std::cout << Line(line) << ClearLine(line) << Color(31, "Error initialize libcurl") << std::flush;
        return 0;
    }

    MemoryHolder mHolder {};
    mHolder.filename = filename;
    mHolder.line = line;

    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, true);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, false);

#ifndef NO_PROXY
    curl_easy_setopt(curl, CURLOPT_PROXY, "http://127.0.0.1:1080");
    curl_easy_setopt(curl, CURLOPT_PROXYTYPE, CURLPROXY_SOCKS5);
    curl_easy_setopt(curl, CURLOPT_HTTPPROXYTUNNEL, 1L);
#endif

    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, ProgressFunction);
    curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, (void*)&mHolder);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteFunction);

    // send in pre-initialized MemoryHolder for this particular download id
    // note: we need to know number of downloads before downloading
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void*)&mHolder);

    // this is a blocking call
    // when the download is done, then this function call will be returned
    CURLcode res = curl_easy_perform(curl);
    if (res != CURLE_OK)
    {
        // print out error
        std::cout << Line(line) << ClearLine(line) << Color(91, filename + ": Download failed [" + curl_easy_strerror(res) + "]") << std::flush;

        // destroy MemoryHolder of this particular download
        if (mHolder.mem)
        {
            delete(mHolder.mem);
            mHolder.mem = nullptr;
        }
    }
    else
    {
        // write to file
        // good thing, we can define this just once here
        std::ofstream of(filename);
        of.write((const char*)(mHolder.mem), mHolder.size);

        // destroy MemoryHolder of this particular download
        // note: as we don't need this particular data anymore after successfully write
        delete(mHolder.mem);
        mHolder.mem = nullptr;
    }

    curl_easy_cleanup(curl);
    return mHolder.size;
}

int main(int argc, char *argv[])
{
    // initialize curl
    curl_global_init(CURL_GLOBAL_DEFAULT);

    std::vector<std::future<std::size_t>> sizes;

    unsigned line = 1;
    for (const std::string& r: {"8859-1.TXT", "8859-2.TXT", "8859-3.TXT", "8859-4.TXT", "8859-5.TXT",
                         "8859-6.TXT", "8859-7.TXT", "8859-8.TXT", "8859-9.TXT", "8859-10.TXT",
                         "8859-11.TXT", "8859-13.TXT", "8859-14.TXT", "8859-15.TXT", "8859-16.TXT"})
    {
        sizes.emplace_back(std::async(std::launch::async, [r, &line]
            {
                return Download(ROOT_URL + r, r, line++);
            }));
        std::this_thread::sleep_for(std::chrono::milliseconds(16));
    }

    std::size_t total = 0;
    for (auto& s: sizes) total += s.get();

    std::cout << Line(line) << Color(92, "Total bytes downloaded: " + std::to_string(total)) << std::endl;

    curl_global_cleanup();
    return 0;
}

SimpleDownloaders_thread.cpp

/** Downloader app following https://www.youtube.com/watch?v=_z-RS0rXg9s but 
 * use libcurl (C API) with some adjusted API usage. 
 *
 * Compile with
 * g++ -std=c++11 -DNO_PROXY SimpleDownloader.cpp -lpthread -lcurl
 * */

#include <iostream>
#include <fstream>
#include <string>
#include <curl/curl.h>
#include <cstdlib>
#include <cstring>
#include <thread>
#include <vector>
#include <mutex>
#include <atomic>

struct MemoryHolder
{
    char *mem;
    size_t size;
    std::string filename; 
    unsigned line;
};

static const std::string ROOT_URL = "http://iki.fi/bisqwit/ctu85/";

static unsigned ln = 1;
static std::string Color(int n, const std::string& s)
{
    return "\33[" + std::to_string(n) + 'm' + s + "\33[m";
}
static std::string Line(int l)
{
    int m = l - ln;
    ln = l;

    return "\r" + (m < 0 ? "\33[" + std::to_string(-m) + 'A': std::string(m, '\n'));
}
static std::string ClearLine(int l)
{
    return "\33[2K";
}

static std::mutex PrintLock;

static int ProgressFunction(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow)
{
    // scope mutex lock
    std::lock_guard<std::mutex> lock(PrintLock);

    MemoryHolder mHolder = *(MemoryHolder*)clientp;
    std::cout << Line(mHolder.line) << ClearLine(mHolder.line) << Color(93, mHolder.filename + ": ") << dlnow << " of " << dltotal
    << " bytes received (" << int(dltotal ? dlnow * 100.0/dltotal : 0) << "%)" << std::flush;

    return 0;    
}

static size_t WriteFunction(char *contents, std::size_t size, std::size_t nmemb, void *userp)
{
    size_t realsize = size * nmemb;
    MemoryHolder *mholder = (MemoryHolder*)userp;

    // memory chunk needs to be allocated first
    // this will ensure it will before we call realloc()
    if (mholder->mem == nullptr)
        mholder->mem = (char*)std::malloc(1);

    char *ptr = (char*)std::realloc(mholder->mem, mholder->size + realsize + 1);
    if (!ptr)
    {
        // out of memory
        std::cout << Line(mholder->line) << ClearLine(mholder->line) << Color(31, "Not enough memory") << std::flush;
        // return number of bytes that handled which we didn't handle any
        return 0;
    }

    // set new memory location that has been re-allocated
    mholder->mem = ptr;
    std::memcpy(&(mholder->mem[mholder->size]), contents, realsize);
    mholder->size += realsize;
    // set null-terminated character
    mholder->mem[mholder->size] = 0;

    return realsize;
}

static std::size_t Download(const std::string& url, const std::string& filename, const unsigned line)
{
    CURL *curl = curl_easy_init();
    if (!curl)
    {
        std::cout << Line(line) << ClearLine(line) << Color(31, "Error initialize libcurl") << std::flush;
        return 0;
    }

    MemoryHolder mHolder {};
    mHolder.filename = filename;
    mHolder.line = line;

    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, true);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, false);

#ifndef NO_PROXY
    curl_easy_setopt(curl, CURLOPT_PROXY, "http://127.0.0.1:1080");
    curl_easy_setopt(curl, CURLOPT_PROXYTYPE, CURLPROXY_SOCKS5);
    curl_easy_setopt(curl, CURLOPT_HTTPPROXYTUNNEL, 1L);
#endif

    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, ProgressFunction);
    curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, (void*)&mHolder);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteFunction);

    // send in pre-initialized MemoryHolder for this particular download id
    // note: we need to know number of downloads before downloading
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void*)&mHolder);

    // this is a blocking call
    // when the download is done, then this function call will be returned
    CURLcode res = curl_easy_perform(curl);
    if (res != CURLE_OK)
    {
        // print out error
        std::cout << Line(line) << ClearLine(line) << Color(91, filename + ": Download failed [" + curl_easy_strerror(res) + "]") << std::flush;

        // destroy MemoryHolder of this particular download
        if (mHolder.mem)
        {
            delete(mHolder.mem);
            mHolder.mem = nullptr;
        }
    }
    else
    {
        // write to file
        // good thing, we can define this just once here
        std::ofstream of(filename);
        of.write((const char*)(mHolder.mem), mHolder.size);

        // destroy MemoryHolder of this particular download
        // note: as we don't need this particular data anymore after successfully write
        delete(mHolder.mem);
        mHolder.mem = nullptr;
    }

    curl_easy_cleanup(curl);
    return mHolder.size;
}

int main(int argc, char *argv[])
{
    // initialize curl
    curl_global_init(CURL_GLOBAL_DEFAULT);

    std::vector<std::thread> downloaders;
    std::vector<std::size_t> sizes;
    std::mutex sizeLock;

    unsigned line = 1;
    for (const std::string& r: {"8859-1.TXT", "8859-2.TXT", "8859-3.TXT", "8859-4.TXT", "8859-5.TXT",
                         "8859-6.TXT", "8859-7.TXT", "8859-8.TXT", "8859-9.TXT", "8859-10.TXT",
                         "8859-11.TXT", "8859-13.TXT", "8859-14.TXT", "8859-15.TXT", "8859-16.TXT"})
    {
        downloaders.emplace_back([r, &line, &sizes, &sizeLock]
            {
                auto size = Download(ROOT_URL + r, r, line++);
                sizeLock.lock();
                sizes.push_back(size);
                sizeLock.unlock();
            });
        std::this_thread::sleep_for(std::chrono::milliseconds(16));
    }

    // it could happen that if downloading is very fast, some of threads might go through
    // but it won't happen in this case
    // for safety, we could always wait for a few first threasd to be finished right inside
    // the initialization loop above
    for (auto& t: downloaders)
    {
        t.join();
    }

    std::size_t total = 0;
    for (auto s: sizes) total += s;

    std::cout << Line(line) << Color(92, "Total bytes downloaded: " + std::to_string(total)) << std::endl;

    curl_global_cleanup();
    return 0;
}