memcheck: fix race in libgit2...

...caused by incorrectly setting and resetting the library internal
state and the misuse of pthreads in libgit2.

Normally, git_libgit2_init and git_libgit2_shutdown should span the
life of a worker thread in order to be safely used. However, due to
an incorrect implementation of libgit2's threadstate with pthreads,
on unix systems there is a race condition.

Until the use of pthread_key_t is corrected in libgit2, we need to
apply a workaround by always ensuring that the main thread is the
first thread reaching the GitContext constructor.

1 files changed, 1 insertions, 3 deletions

diff --git a/src/buildtool/file_system/git_cas.hpp b/src/buildtool/file_system/git_cas.hpp
index f95cb403..3ef8b6d8 100644
--- a/src/buildtool/file_system/git_cas.hpp
+++ b/src/buildtool/file_system/git_cas.hpp
@@ -34,7 +34,7 @@ class GitCAS {
     static auto Open(std::filesystem::path const& repo_path) noexcept
         -> GitCASPtr;
 
-    GitCAS() noexcept = default;
+    GitCAS() noexcept;
     ~GitCAS() noexcept = default;
 
     // prohibit moves and copies
@@ -62,8 +62,6 @@ class GitCAS {
         -> std::optional<std::pair<std::size_t, ObjectType>>;
 
   private:
-    // IMPORTANT: the GitContext needs to be initialized before any git object!
-    GitContext git_context_{};  // maintains a Git context while CAS is alive
     std::unique_ptr<git_odb, decltype(&odb_closer)> odb_{nullptr, odb_closer};
     // git folder path of repo
     std::filesystem::path git_path_{};