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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - std::filesystem::weakly_canonical race condition when the underlying path is removed"
href="https://bugs.llvm.org/show_bug.cgi?id=49493">49493</a>
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<th>Summary</th>
<td>std::filesystem::weakly_canonical race condition when the underlying path is removed
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>10.0
</td>
</tr>
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<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>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>xavier.roche@algolia.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<pre>Created <span class=""><a href="attachment.cgi?id=24609" name="attach_24609" title="Test aimed to reproduce the race issue">attachment 24609</a> <a href="attachment.cgi?id=24609&action=edit" title="Test aimed to reproduce the race issue">[details]</a></span>
Test aimed to reproduce the race issue
The std::filesystem::weakly_canonical function is normally able to canonize
both non-existing path(es) and existing path(es).
However, the current implementation is having issues with canonizing a path
that disappears while the function is being called, leading to randomly
returning errors (and/or raising filesystem_error).
Important Note: this MAY be an expected behavior, as the official specification
of std::filesystem::weakly_canonical does not appear to be completely clear
towards impact of filesystem volatility.
The attached sample demonstrate the issue:
-----------------------------------------
clang++ -g3 -pthread -std=c++20 filesystem_weakly_canonical-race-canonical.cpp
-o filesystem_weakly_canonical-race-canonical
./filesystem_weakly_canonical-race-canonical
Starting computing
terminate called after throwing an instance of
'std::filesystem::__cxx11::filesystem_error'
what(): filesystem error: cannot make canonical path: No such file or
directory [foo]
Aborted (core dumped)
Our understanding is that std::filesystem::weakly_canonical calls
std::filesystem::canonical under the hood, if the path segment exist:
while (PP.State != PathParser::PS_BeforeBegin) {
tmp.assign(createView(p.native().data(), &PP.RawEntry.back()));
error_code m_ec;
file_status st = __status(tmp, &m_ec);
if (!status_known(st)) {
return err.report(m_ec);
} else if (exists(st)) {
result = __canonical(tmp, ec);
break;
}
DNEParts.push_back(*PP);
--PP;
}</pre>
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