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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - std::async with default policy moves their arguments twice if std::thread cannot be created"
href="https://llvm.org/bugs/show_bug.cgi?id=28285">28285</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>std::async with default policy moves their arguments twice if std::thread cannot be created
</td>
</tr>
<tr>
<th>Product</th>
<td>libc++
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kariya_mitsuru@hotmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>In the libc++'s current implementation of std::async with default policy (i.e.
async | deferred),
first, the argument function is launched in the context of a new thread
asynchronously (async).
If it was failed, the function is launched in the context of the current thread
later (deffered).
But if the first launch was failed (ex. std::thread creation trows an
exception), std::async's
arguments was already moved.
So, the arguments have no valid values when second launch is executing.
The sample code below simulates std::thread creation failure.
============================== sample code ==============================
#include <iostream>
#include <future>
#include <string>
#include <system_error>
struct S {
S() : b(false) {}
// to simulate thread creation failure, it throws
resource_unavailable_try_again when 'o' is first move target
S(S&& o) : b(true) {
if (!o.b) {
o.b = true;
throw
std::system_error(std::make_error_code(std::errc::resource_unavailable_try_again));
}
}
S(const S&) = delete;
S& operator=(const S&) = delete;
S&& operator=(S&&) = delete;
bool b;
};
int main()
{
auto f = std::async([](std::string&& s, S&&){ std::cout << "s = '" << s <<
'\'' << std::endl; }, std::string{"str"}, S{});
f.get();
}
============================== sample code ==============================
============================== output ==============================
s = ''
============================== output ==============================
cf. <a href="http://melpon.org/wandbox/permlink/IZDRW8D7i0wifN91">http://melpon.org/wandbox/permlink/IZDRW8D7i0wifN91</a>
I think that it should output "s = 'str'" or should output nothing,
whether exception is thrown or not.</pre>
</div>
</p>
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