[libcxx-commits] [PATCH] D122612: [libcxx] [test] Fix back-to-back use of get_temp_file_name() on Windows

[Martin Storsjö via Phabricator via libcxx-commits]

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On non-Windows platforms, get_temp_file_name() uses `mkstemp()`,
which picks a unique name and creates a file atomically. The
Windows implementation uses `_mktemp_s()`, which doesn't create the
file. The documentation of `_mktemp_s()` also says that by design,
the function uses the same pattern within a process, as long as that
file doesn't exist.

Thus previously, two consecutive calls to `get_temp_file_name()`
on Windows returned the same file name.

By creating the file (with a plain `fopen(, "w")` we mark the file
name as taken for later calls. As this isn't atomic, this could
lead to duplicates if there'd be multiple calls to
`get_temp_file_name()` in multiple threads in the same test process
in parallel, but that's probably not done in these tests.
(`_mktemp_s` does guard against clashes between parallel processes
though, so there's no risk of clashes between multiple tests
executing in paralle.)

This fixes the test failures on Windows observed in D122257 <https://reviews.llvm.org/D122257>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122612

Files:
  libcxx/test/support/platform_support.h


Index: libcxx/test/support/platform_support.h
===================================================================
--- libcxx/test/support/platform_support.h
+++ libcxx/test/support/platform_support.h
@@ -55,6 +55,9 @@
 #if defined(_WIN32)
     char Name[] = "libcxx.XXXXXX";
     if (_mktemp_s(Name, sizeof(Name)) != 0) abort();
+    FILE *File = fopen(Name, "wb");
+    if (File)
+        fclose(File);
     return Name;
 #else
     std::string Name;


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