import quincy beta 17.1.0

[ceph.git] / ceph / src / boost / libs / leaf / examples / capture_in_result.cpp

diff --git a/ceph/src/boost/libs/leaf/examples/capture_in_result.cpp b/ceph/src/boost/libs/leaf/examples/capture_in_result.cpp
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+++ b/ceph/src/boost/libs/leaf/examples/capture_in_result.cpp
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+// Copyright (c) 2018-2020 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, without using exception handling. See capture_eh.cpp
+// for the version that uses exception handling.
+
+#include <boost/leaf/capture.hpp>
+#include <boost/leaf/handle_errors.hpp>
+#include <boost/leaf/result.hpp>
+#include <vector>
+#include <string>
+#include <future>
+#include <iterator>
+#include <iostream>
+#include <algorithm>
+
+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...
+leaf::result<task_result> task()
+{
+    bool succeed = (rand()%4) != 0; //...at random.
+    if( succeed )
+        return { };
+    else
+        return leaf::new_error(
+            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_handle_all 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<leaf::result<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 of an error. 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_handle_all(
+            [&]() -> leaf::result<void>
+            {
+                BOOST_LEAF_AUTO(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.
+                return { };
+            },
+            error_handlers );
+    }
+}
+
+////////////////////////////////////////
+
+#ifdef BOOST_LEAF_NO_EXCEPTIONS
+
+namespace boost
+{
+    BOOST_LEAF_NORETURN void throw_exception( std::exception const & e )
+    {
+        std::cerr << "Terminating due to a C++ exception under BOOST_LEAF_NO_EXCEPTIONS: " << e.what();
+        std::terminate();
+    }
+
+    struct source_location;
+    BOOST_LEAF_NORETURN void throw_exception( std::exception const & e, boost::source_location const & )
+    {
+        throw_exception(e);
+    }
+}
+
+#endif