GitRepo: Guard fake repository odb wrapping

In the current libgit2 implementation, a fake repository wrapped
around an existing odb is being registered as owner the same way
as a normal repository object. Therefore, one has to guard both
the creation and destruction of the fake repository against all
other git operations that might access the internal cache during
this transfer of ownership.

1 files changed, 19 insertions, 13 deletions

diff --git a/src/buildtool/file_system/git_cas.cpp b/src/buildtool/file_system/git_cas.cpp
index 2a4a7142..1f8525fe 100644
--- a/src/buildtool/file_system/git_cas.cpp
+++ b/src/buildtool/file_system/git_cas.cpp
@@ -81,12 +81,15 @@ auto GitCAS::ReadObject(std::string const& id, bool is_hex_id) const noexcept
     }
 
     git_odb_object* obj = nullptr;
-    if (git_odb_read(&obj, odb_.get(), &oid.value()) != 0) {
-        Logger::Log(LogLevel::Error,
-                    "reading git object {} from database failed with:\n{}",
-                    is_hex_id ? id : ToHexString(id),
-                    GitLastError());
-        return std::nullopt;
+    {
+        std::shared_lock lock{mutex_};
+        if (git_odb_read(&obj, odb_.get(), &oid.value()) != 0) {
+            Logger::Log(LogLevel::Error,
+                        "reading git object {} from database failed with:\n{}",
+                        is_hex_id ? id : ToHexString(id),
+                        GitLastError());
+            return std::nullopt;
+        }
     }
 
     std::string data(static_cast<char const*>(git_odb_object_data(obj)),
@@ -111,13 +114,16 @@ auto GitCAS::ReadHeader(std::string const& id, bool is_hex_id) const noexcept
 
     std::size_t size{};
     git_object_t type{};
-    if (git_odb_read_header(&size, &type, odb_.get(), &oid.value()) != 0) {
-        Logger::Log(LogLevel::Error,
-                    "reading git object header {} from database failed "
-                    "with:\n{}",
-                    is_hex_id ? id : ToHexString(id),
-                    GitLastError());
-        return std::nullopt;
+    {
+        std::shared_lock lock{mutex_};
+        if (git_odb_read_header(&size, &type, odb_.get(), &oid.value()) != 0) {
+            Logger::Log(LogLevel::Error,
+                        "reading git object header {} from database failed "
+                        "with:\n{}",
+                        is_hex_id ? id : ToHexString(id),
+                        GitLastError());
+            return std::nullopt;
+        }
     }
 
     if (auto obj_type = GitTypeToObjectType(type)) {