[llvm-dev] Race condition in raw_ostream

[Viacheslav Nikolaev via llvm-dev]

This code from raw_ostream.h is really racy:

  raw_ostream &operator<<(StringRef Str) {
    // Inline fast path, particularly for strings with a known length.
    size_t Size = Str.size();

    // Make sure we can use the fast path.
    if (Size > (size_t)(OutBufEnd - OutBufCur))
      return write(Str.data(), Size);

    if (Size) {
      memcpy(OutBufCur, Str.data(), Size);
      OutBufCur += Size;
    }
    return *this;
  }


Of course, one might wonder why someone would need to output to a stream
from multiple threads at the same time.

But imagine someone might get logs to dbgs() or errs() running the backend
for a target in multiple threads.
Is there any known practice to avoid such a problem?
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