1 files changed, 26 insertions, 2 deletions
diff --git a/library/cpp/yt/system/thread_id.cpp b/library/cpp/yt/system/thread_id.cpp
index a1971dd0dd8..978c735df25 100644
--- a/library/cpp/yt/system/thread_id.cpp
+++ b/library/cpp/yt/system/thread_id.cpp
@@ -2,19 +2,43 @@
 
 #include <util/system/thread.h>
 
+#ifdef _unix_
+#include <library/cpp/yt/misc/static_initializer.h>
+
+#include <pthread.h>
+#endif
+
 namespace NYT {
 
 ////////////////////////////////////////////////////////////////////////////////
 
+YT_DEFINE_THREAD_LOCAL(TSystemThreadId, CachedSystemThreadId, InvalidSystemThreadId);
+
 YT_DEFINE_THREAD_LOCAL(TSequentialThreadId, CachedSequentialThreadId, InvalidSequentialThreadId);
 std::atomic<TSequentialThreadId> SequentialThreadIdGenerator = InvalidSequentialThreadId;
 
-TSystemThreadId GetSystemThreadId()
+namespace NDetail {
+
+TSystemThreadId GetSystemThreadIdImpl()
 {
     static_assert(std::is_same_v<TSystemThreadId, ::TThread::TId>);
     return ::TThread::CurrentThreadNumericId();
 }
 
+} // namespace NDetail
+
+#ifdef _unix_
+// The kernel tid is stable for the lifetime of a thread, so we cache it to
+// avoid the |gettid| syscall on each call. After a |fork|, however, the
+// surviving (calling) thread of the child gets a fresh kernel tid, so the
+// cache must be invalidated there.
+YT_STATIC_INITIALIZER(
+    ::pthread_atfork(
+        /*prepare*/ nullptr,
+        /*parent*/  nullptr,
+        /*child*/   [] { CachedSystemThreadId() = InvalidSystemThreadId; }));
+#endif
+
 ////////////////////////////////////////////////////////////////////////////////
 
-} // namespace NYT::NThreading
+} // namespace NYT