Subj : Re: Is std::cerr thread safe
To   : comp.programming.threads
From : Sean Kelly
Date : Wed Jul 20 2005 01:04 pm

The STL is guaranteed to be thread-safe, but thread safety in this case
just means that it won't crash horribly if you use it in a
multi-threaded program.  In my experience, writing to std::cerr from
multiple threads works just fine, but the elements may be intermixed if
writes are simultaneous.  A fairly cheap way around this is to do every
write into a stringstream and then dump it en masse into the error
stream:

std::ostringstream ostr;
ostr << "error: " << errno << '\n';
std::cerr << ostr.rdbuf();

The preferable alternative would be to wrap writes in a critical
section or create your own error stream that does something like using
thread local storage for its buffer and only flushes when explicitly
instructed to do so.


Sean

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