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// Copyright 2018-2022 Emil Dotchevski and Reverge Studios, Inc.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// This is a simple program that demonstrates the use of LEAF to transport error
// objects between threads, using exception handling. See capture_in_result.cpp
// for the version that does not use exception handling.
#include <boost/leaf.hpp>
#include <vector>
#include <string>
#include <future>
#include <iterator>
#include <iostream>
#include <algorithm>
#include <thread>
namespace leaf = boost::leaf;
// Define several error types.
struct e_thread_id { std::thread::id value; };
struct e_failure_info1 { std::string value; };
struct e_failure_info2 { int value; };
// A type that represents a successfully returned result from a task.
struct task_result { };
// This is our task function. It produces objects of type task_result, but it
// may fail.
task_result task()
{
bool succeed = (rand()%4) != 0; //...at random.
if( succeed )
return { };
else
leaf::throw_exception(
e_thread_id{std::this_thread::get_id()},
e_failure_info1{"info"},
e_failure_info2{42} );
};
int main()
{
int const task_count = 42;
// The error_handlers are used in this thread (see leaf::try_catch below).
// The arguments passed to individual lambdas are transported from the
// worker thread to the main thread automatically.
auto error_handlers = std::make_tuple(
[]( e_failure_info1 const & v1, e_failure_info2 const & v2, e_thread_id const & tid )
{
std::cerr << "Error in thread " << tid.value << "! failure_info1: " << v1.value << ", failure_info2: " << v2.value << std::endl;
},
[]( leaf::diagnostic_info const & unmatched )
{
std::cerr <<
"Unknown failure detected" << std::endl <<
"Cryptic diagnostic information follows" << std::endl <<
unmatched;
} );
// Container to collect the generated std::future objects.
std::vector<std::future<task_result>> fut;
// Launch the tasks, but rather than launching the task function directly,
// we launch a wrapper function which calls leaf::capture, passing a context
// object that will hold the error objects reported from the task in case it
// throws. The error types the context is able to hold statically are
// automatically deduced from the type of the error_handlers tuple.
std::generate_n( std::back_inserter(fut), task_count,
[&]
{
return std::async(
std::launch::async,
[&]
{
return leaf::capture(leaf::make_shared_context(error_handlers), &task);
} );
} );
// Wait on the futures, get the task results, handle errors.
for( auto & f : fut )
{
f.wait();
leaf::try_catch(
[&]
{
task_result r = f.get();
// Success! Use r to access task_result.
std::cout << "Success!" << std::endl;
(void) r; // Presumably we'll somehow use the task_result.
},
error_handlers );
}
}
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