Allow Boehm to mark from thread-locals #106
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On UNIX this means that thread_local! will use the pthread specific API instead of LLVM's compiler's __thread implementation. This also means we must disable tests which rely on compiler supported TLS.
This introduces a thread-local rootset vector, which holds pointers to the current thread's TL values. This rootset is then specifically added to Boehm's mark list so that TL values can be traced.
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In order to support this this PR is split into two commits:
We must disable compiler-based thread local implementation. This is a shame because it's faster than the POSIX thread library impl but it places thread locals in a table in a segment in the binary which Boehm can't scan. It might be possible to fix this in the future, but for now we fallback to using the POSIX thread implementation because there exists a fix for this.
We introduce a thread-local rootset vector, which holds pointers to the current thread's TL values. This rootset is then specifically added to Boehm's mark list so that TL values can be traced.