third_party/boost/process/doc/posix_pseudocode.xml

<?xml version="1.0" standalone="yes"?>
<programlisting>
for (auto &amp; s : seq)
    s.<methodname alt="boost::process::extend::handler::on_setup">on_setup</methodname>(*this);

if (<methodname alt="boost::process::extend::posix_executor::error">error</methodname>())
{
    for (auto &amp; s : seq)
       s.<methodname alt="boost::process::extend::handler::on_error">on_error</methodname>(*this, <methodname alt="boost::process::extend::posix_executor::error">error</methodname>());
    return <classname alt="boost::process::child">child</classname>();
}

pid = <ulink url="http://pubs.opengroup.org/onlinepubs/009695399/functions/fork.html">fork()</ulink>
<methodname alt="boost::process::extend::handler::on_setup">on_setup</methodname>(*this);

if (pid == -1) //fork error 
{
    <methodname alt="boost::process::extend::posix_executor::set_error">set_error</methodname>(<functionname alt="boost::process::extend::get_last_error">get_last_error</functionname>());
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_fork_error">on_fork_error</methodname>(*this, <methodname alt="boost::process::extend::posix_executor::error">error</methodname>());
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_error">on_error</methodname>(*this, <methodname alt="boost::process::extend::posix_executor::error">error</methodname>());
    return <classname alt="boost::process::child">child</classname>()
}
else if (pid == 0) //child process
{
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_exec_setup">on_exec_setup</methodname>(*this);
    <ulink url="http://pubs.opengroup.org/onlinepubs/009695399/functions/exec.html">execve</ulink>(exe, cmd_line, env);
    auto ec = <functionname alt="boost::process::extend::get_last_error">get_last_error</functionname>();
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_exec_error">on_exec_error</methodname>(*this);

    <emphasis>unspecified();</emphasis>//here the error is send to the father process interally

    <ulink url="http://en.cppreference.com/w/cpp/utility/program/exit">std::exit</ulink>(<ulink url="http://en.cppreference.com/w/c/program/EXIT_status">EXIT_FAILURE</ulink>);
    return <classname alt="boost::process::child">child</classname>(); //for C++ compliance
}

<classname alt="boost::process::child">child</classname> c(pid, exit_code);

<emphasis>unspecified();</emphasis>//here, we read the the error from the child process

if (<methodname alt="boost::process::extend::posix_executor::error">error</methodname>())
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_error">on_error</methodname>(*this, <methodname alt="boost::process::extend::posix_executor::error">error</methodname>());
else
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_error">on_success</methodname>(*this);

//now we check again, because a on_success handler might've errored.
if (<methodname alt="boost::process::extend::posix_executor::error">error</methodname>())
{
    for (auto &amp; s : seq)
        s.<methodname alt="boost::process::extend::handler::on_error">on_error</methodname>(*this, <methodname alt="boost::process::extend::posix_executor::error">error</methodname>());
    return <classname alt="boost::process::child">child</classname>();
}
else
    return c;
</programlisting>