我正在实现一个TCP客户端，该客户端可以读取和发送文件和字符串，并且我将Boost用作主库。我想继续读取或发送文件，同时继续发送字符串，在这种情况下，这是要发送到服务器的命令。为此，我考虑过使用线程池以不使客户端过载。我的问题是，当池中的线程结束时，我可以使用 future 来使用回调吗？万一我不能，还有其他解决办法吗？
我正在做这样的事情，其中pool_是boost:asio:thread_pool
void send_file(std::string const& file_path){
boost::asio::post(pool_, [this, &file_path] {
handle_send_file(file_path);
});
// DO SOMETHING WHEN handle_send_file ENDS
}
void handle_send_file(std::string const& file_path) {
boost::array<char, 1024> buf{};
boost::system::error_code error;
std::ifstream source_file(file_path, std::ios_base::binary | std::ios_base::ate);
if(!source_file) {
std::cout << "[ERROR] Failed to open " << file_path << std::endl;
//TODO gestire errore
}
size_t file_size = source_file.tellg();
source_file.seekg(0);
std::string file_size_readable = file_size_to_readable(file_size);
// First send file name and file size in bytes to server
boost::asio::streambuf request;
std::ostream request_stream(&request);
request_stream << file_path << "\n"
<< file_size << "\n\n"; // Consider sending readable version, does it change anything?
// Send the request
boost::asio::write(*socket_, request, error);
if(error){
std::cout << "[ERROR] Send request error:" << error << std::endl;
//TODO lanciare un'eccezione? Qua dovrò controllare se il server funziona o no
}
if(DEBUG) {
std::cout << "[DEBUG] " << file_path << " size is: " << file_size_readable << std::endl;
std::cout << "[DEBUG] Start sending file content" << std::endl;
}
long bytes_sent = 0;
float percent = 0;
print_percentage(percent);
while(!source_file.eof()) {
source_file.read(buf.c_array(), (std::streamsize)buf.size());
int bytes_read_from_file = source_file.gcount(); //int is fine because i read at most buf's size, 1024 in this case
if(bytes_read_from_file<=0) {
std::cout << "[ERROR] Read file error" << std::endl;
break;
//TODO gestire questo errore
}
percent = std::ceil((100.0 * bytes_sent) / file_size);
print_percentage(percent);
boost::asio::write(*socket_, boost::asio::buffer(buf.c_array(), source_file.gcount()),
boost::asio::transfer_all(), error);
if(error) {
std::cout << "[ERROR] Send file error:" << error << std::endl;
//TODO lanciare un'eccezione?
}
bytes_sent += bytes_read_from_file;
}
std::cout << "\n" << "[INFO] File " << file_path << " sent successfully!" << std::endl;
}
最佳答案
发布到池的操作结束，而线程没有结束。这就是池化线程的全部目的。
void send_file(std::string const& file_path){
post(pool_, [this, &file_path] {
handle_send_file(file_path);
});
// DO SOMETHING WHEN handle_send_file ENDS
}
file_path，因为该参数很快就会超出范围，并且handle_send_file调用将在另一个线程中的未指定时间运行。那是比赛条件和悬而未决的引用。 Undefined Behaviour结果。然后
// DO SOMETHING WHEN handle_send_file ENDS
handle_send_file没有序列关系的线上。实际上，它可能会在该操作有机会开始之前运行。简化
这是一个简化的版本:
#include <boost/array.hpp>
#include <boost/asio.hpp>
#include <fstream>
#include <iostream>
namespace asio = boost::asio;
using asio::ip::tcp;
static asio::thread_pool pool_;
struct X {
std::unique_ptr<tcp::socket> socket_;
explicit X(unsigned short port) : socket_(new tcp::socket{ pool_ }) {
socket_->connect({ {}, port });
}
asio::thread_pool pool_;
std::unique_ptr<tcp::socket> socket_{ new tcp::socket{ pool_ } };
void send_file(std::string file_path) {
post(pool_, [=, this] {
send_file_implementation(file_path);
// DO SOMETHING WHEN send_file_implementation ENDS
});
}
// throws system_error exception
void send_file_implementation(std::string file_path) {
std::ifstream source_file(file_path,
std::ios_base::binary | std::ios_base::ate);
size_t file_size = source_file.tellg();
source_file.seekg(0);
write(*socket_,
asio::buffer(file_path + "\n" + std::to_string(file_size) + "\n\n"));
boost::array<char, 1024> buf{};
while (source_file.read(buf.c_array(), buf.size()) ||
source_file.gcount() > 0)
{
int n = source_file.gcount();
if (n <= 0) {
using namespace boost::system;
throw system_error(errc::io_error, system_category());
}
write(*socket_, asio::buffer(buf), asio::transfer_exactly(n));
}
}
};
X的多个实例，因此您有单独的socket_连接)。最后要做一些事情，只需将代码放在我移动注释的位置:
// DO SOMETHING WHEN send_file_implementation ENDS
std::future<void> send_file(std::string file_path) {
std::packaged_task<void()> task([=, this] {
send_file_implementation(file_path);
});
return post(pool_, std::move(task));
}
post 神奇地¹返回打包任务的 future 。打包的任务将使用(void)返回值或引发的异常来设置内部 promise 。实际操作中查看: Live On Coliru
int main() {
// send two files simultaneously to different connections
X clientA(6868);
X clientB(6969);
std::future<void> futures[] = {
clientA.send_file("main.cpp"),
clientB.send_file("main.cpp"),
};
for (auto& fut : futures) try {
fut.get();
std::cout << "Everything completed without error\n";
} catch(std::exception const& e) {
std::cout << "Error occurred: " << e.what() << "\n";
};
pool_.join();
}
nc -l -p 6868 | head& nc -l -p 6969 | md5sum&
./a.out
wait
Everything completed without error
Everything completed without error
main.cpp
1907
#include <boost/array.hpp>
#include <boost/asio.hpp>
#include <fstream>
#include <iostream>
#include <future>
namespace asio = boost::asio;
using asio::ip::tcp;
7ecb71992bcbc22bda44d78ad3e2a5ef -
¹不是魔术:请参阅https://www.boost.org/doc/libs/1_66_0/doc/html/boost_asio/reference/async_result.html