Index: lib/asan/asan_fuchsia.cc
===================================================================
--- lib/asan/asan_fuchsia.cc
+++ lib/asan/asan_fuchsia.cc
@@ -178,7 +178,7 @@
   SetCurrentThread(thread);
 
   // In lieu of AsanThread::ThreadStart.
-  asanThreadRegistry().StartThread(thread->tid(), os_id, /*workerthread*/ false,
+  asanThreadRegistry().StartThread(thread->tid(), os_id, ThreadType::Regular,
                                    nullptr);
 }
 
Index: lib/asan/asan_mac.cc
===================================================================
--- lib/asan/asan_mac.cc
+++ lib/asan/asan_mac.cc
@@ -181,8 +181,8 @@
     t = AsanThread::Create(/* start_routine */ nullptr, /* arg */ nullptr,
                            parent_tid, stack, /* detached */ true);
     t->Init();
-    asanThreadRegistry().StartThread(t->tid(), GetTid(),
-                                     /* workerthread */ true, 0);
+    asanThreadRegistry().StartThread(t->tid(), GetTid(), ThreadType::Worker,
+                                     nullptr);
     SetCurrentThread(t);
   }
 }
Index: lib/asan/asan_rtems.cc
===================================================================
--- lib/asan/asan_rtems.cc
+++ lib/asan/asan_rtems.cc
@@ -183,8 +183,8 @@
   // Determine whether we are starting or restarting the thread.
   if (status == ThreadStatusCreated)
     // In lieu of AsanThread::ThreadStart.
-    asanThreadRegistry().StartThread(thread->tid(), os_id,
-                                     /*workerthread*/ false, nullptr);
+    asanThreadRegistry().StartThread(thread->tid(), os_id, ThreadType::Regular,
+                                     nullptr);
   else {
     // In a thread restart, a thread may resume execution at an
     // arbitrary function entry point, with its stack and TLS state
Index: lib/asan/asan_thread.cc
===================================================================
--- lib/asan/asan_thread.cc
+++ lib/asan/asan_thread.cc
@@ -245,8 +245,7 @@
 thread_return_t AsanThread::ThreadStart(
     tid_t os_id, atomic_uintptr_t *signal_thread_is_registered) {
   Init();
-  asanThreadRegistry().StartThread(tid(), os_id, /*workerthread*/ false,
-                                   nullptr);
+  asanThreadRegistry().StartThread(tid(), os_id, ThreadType::Regular, nullptr);
   if (signal_thread_is_registered)
     atomic_store(signal_thread_is_registered, 1, memory_order_release);
 
Index: lib/lsan/lsan_thread.h
===================================================================
--- lib/lsan/lsan_thread.h
+++ lib/lsan/lsan_thread.h
@@ -44,7 +44,8 @@
 
 void InitializeThreadRegistry();
 
-void ThreadStart(u32 tid, tid_t os_id, bool workerthread = false);
+void ThreadStart(u32 tid, tid_t os_id,
+                 ThreadType thread_type = ThreadType::Regular);
 void ThreadFinish();
 u32 ThreadCreate(u32 tid, uptr uid, bool detached);
 void ThreadJoin(u32 tid);
Index: lib/lsan/lsan_thread.cc
===================================================================
--- lib/lsan/lsan_thread.cc
+++ lib/lsan/lsan_thread.cc
@@ -76,7 +76,7 @@
                                        /* arg */ nullptr);
 }
 
-void ThreadStart(u32 tid, tid_t os_id, bool workerthread) {
+void ThreadStart(u32 tid, tid_t os_id, ThreadType thread_type) {
   OnStartedArgs args;
   uptr stack_size = 0;
   uptr tls_size = 0;
@@ -86,7 +86,7 @@
   args.tls_end = args.tls_begin + tls_size;
   GetAllocatorCacheRange(&args.cache_begin, &args.cache_end);
   args.dtls = DTLS_Get();
-  thread_registry->StartThread(tid, os_id, workerthread, &args);
+  thread_registry->StartThread(tid, os_id, thread_type, &args);
 }
 
 void ThreadFinish() {
Index: lib/sanitizer_common/sanitizer_thread_registry.h
===================================================================
--- lib/sanitizer_common/sanitizer_thread_registry.h
+++ lib/sanitizer_common/sanitizer_thread_registry.h
@@ -28,6 +28,11 @@
   ThreadStatusDead       // Joined, but some info is still available.
 };
 
+enum class ThreadType {
+  Regular, // Normal thread
+  Worker,  // macOS Grand Central Dispatch (GCD) worker thread
+};
+
 // Generic thread context. Specific sanitizer tools may inherit from it.
 // If thread is dead, context may optionally be reused for a new thread.
 class ThreadContextBase {
@@ -44,7 +49,7 @@
 
   ThreadStatus status;
   bool detached;
-  bool workerthread;
+  ThreadType thread_type;
 
   u32 parent_tid;
   ThreadContextBase *next;  // For storing thread contexts in a list.
@@ -56,7 +61,7 @@
   void SetDead();
   void SetJoined(void *arg);
   void SetFinished();
-  void SetStarted(tid_t _os_id, bool _workerthread, void *arg);
+  void SetStarted(tid_t _os_id, ThreadType _thread_type, void *arg);
   void SetCreated(uptr _user_id, u64 _unique_id, bool _detached,
                   u32 _parent_tid, void *arg);
   void Reset();
@@ -120,7 +125,7 @@
   void DetachThread(u32 tid, void *arg);
   void JoinThread(u32 tid, void *arg);
   void FinishThread(u32 tid);
-  void StartThread(u32 tid, tid_t os_id, bool workerthread, void *arg);
+  void StartThread(u32 tid, tid_t os_id, ThreadType thread_type, void *arg);
   void SetThreadUserId(u32 tid, uptr user_id);
 
  private:
Index: lib/sanitizer_common/sanitizer_thread_registry.cc
===================================================================
--- lib/sanitizer_common/sanitizer_thread_registry.cc
+++ lib/sanitizer_common/sanitizer_thread_registry.cc
@@ -17,8 +17,8 @@
 
 ThreadContextBase::ThreadContextBase(u32 tid)
     : tid(tid), unique_id(0), reuse_count(), os_id(0), user_id(0),
-      status(ThreadStatusInvalid),
-      detached(false), workerthread(false), parent_tid(0), next(0) {
+      status(ThreadStatusInvalid), detached(false),
+      thread_type(ThreadType::Regular), parent_tid(0), next(0) {
   name[0] = '\0';
   atomic_store(&thread_destroyed, 0, memory_order_release);
 }
@@ -70,11 +70,11 @@
   OnFinished();
 }
 
-void ThreadContextBase::SetStarted(tid_t _os_id, bool _workerthread,
+void ThreadContextBase::SetStarted(tid_t _os_id, ThreadType _thread_type,
                                    void *arg) {
   status = ThreadStatusRunning;
   os_id = _os_id;
-  workerthread = _workerthread;
+  thread_type = _thread_type;
   OnStarted(arg);
 }
 
@@ -302,7 +302,7 @@
   tctx->SetDestroyed();
 }
 
-void ThreadRegistry::StartThread(u32 tid, tid_t os_id, bool workerthread,
+void ThreadRegistry::StartThread(u32 tid, tid_t os_id, ThreadType thread_type,
                                  void *arg) {
   BlockingMutexLock l(&mtx_);
   running_threads_++;
@@ -310,7 +310,7 @@
   ThreadContextBase *tctx = threads_[tid];
   CHECK_NE(tctx, 0);
   CHECK_EQ(ThreadStatusCreated, tctx->status);
-  tctx->SetStarted(os_id, workerthread, arg);
+  tctx->SetStarted(os_id, thread_type, arg);
 }
 
 void ThreadRegistry::QuarantinePush(ThreadContextBase *tctx) {
Index: lib/tsan/go/tsan_go.cc
===================================================================
--- lib/tsan/go/tsan_go.cc
+++ lib/tsan/go/tsan_go.cc
@@ -213,7 +213,7 @@
   ThreadState *thr = AllocGoroutine();
   *pthr = thr;
   int goid = ThreadCreate(parent, (uptr)pc, 0, true);
-  ThreadStart(thr, goid, 0, /*workerthread*/ false);
+  ThreadStart(thr, goid, 0, ThreadType::Regular);
 }
 
 void __tsan_go_end(ThreadState *thr) {
Index: lib/tsan/rtl/tsan_interceptors.cc
===================================================================
--- lib/tsan/rtl/tsan_interceptors.cc
+++ lib/tsan/rtl/tsan_interceptors.cc
@@ -958,7 +958,7 @@
       internal_sched_yield();
     Processor *proc = ProcCreate();
     ProcWire(proc, thr);
-    ThreadStart(thr, tid, GetTid(), /*workerthread*/ false);
+    ThreadStart(thr, tid, GetTid(), ThreadType::Regular);
     atomic_store(&p->tid, 0, memory_order_release);
   }
   void *res = callback(param);
Index: lib/tsan/rtl/tsan_platform_mac.cc
===================================================================
--- lib/tsan/rtl/tsan_platform_mac.cc
+++ lib/tsan/rtl/tsan_platform_mac.cc
@@ -212,7 +212,7 @@
       ThreadState *parent_thread_state = nullptr;  // No parent.
       int tid = ThreadCreate(parent_thread_state, 0, (uptr)thread, true);
       CHECK_NE(tid, 0);
-      ThreadStart(thr, tid, GetTid(), /*workerthread*/ true);
+      ThreadStart(thr, tid, GetTid(), ThreadType::Worker);
     }
   } else if (event == PTHREAD_INTROSPECTION_THREAD_TERMINATE) {
     if (thread == pthread_self()) {
Index: lib/tsan/rtl/tsan_report.h
===================================================================
--- lib/tsan/rtl/tsan_report.h
+++ lib/tsan/rtl/tsan_report.h
@@ -13,6 +13,7 @@
 #define TSAN_REPORT_H
 
 #include "sanitizer_common/sanitizer_symbolizer.h"
+#include "sanitizer_common/sanitizer_thread_registry.h"
 #include "sanitizer_common/sanitizer_vector.h"
 #include "tsan_defs.h"
 
@@ -91,7 +92,7 @@
   int id;
   tid_t os_id;
   bool running;
-  bool workerthread;
+  ThreadType thread_type;
   char *name;
   u32 parent_tid;
   ReportStack *stack;
Index: lib/tsan/rtl/tsan_report.cc
===================================================================
--- lib/tsan/rtl/tsan_report.cc
+++ lib/tsan/rtl/tsan_report.cc
@@ -257,7 +257,7 @@
     Printf(" '%s'", rt->name);
   char thrbuf[kThreadBufSize];
   const char *thread_status = rt->running ? "running" : "finished";
-  if (rt->workerthread) {
+  if (rt->thread_type == ThreadType::Worker) {
     Printf(" (tid=%zu, %s) is a GCD worker thread\n", rt->os_id, thread_status);
     Printf("\n");
     Printf("%s", d.Default());
Index: lib/tsan/rtl/tsan_rtl.h
===================================================================
--- lib/tsan/rtl/tsan_rtl.h
+++ lib/tsan/rtl/tsan_rtl.h
@@ -764,7 +764,8 @@
 void FuncExit(ThreadState *thr);
 
 int ThreadCreate(ThreadState *thr, uptr pc, uptr uid, bool detached);
-void ThreadStart(ThreadState *thr, int tid, tid_t os_id, bool workerthread);
+void ThreadStart(ThreadState *thr, int tid, tid_t os_id,
+                 ThreadType thread_type);
 void ThreadFinish(ThreadState *thr);
 int ThreadTid(ThreadState *thr, uptr pc, uptr uid);
 void ThreadJoin(ThreadState *thr, uptr pc, int tid);
Index: lib/tsan/rtl/tsan_rtl.cc
===================================================================
--- lib/tsan/rtl/tsan_rtl.cc
+++ lib/tsan/rtl/tsan_rtl.cc
@@ -396,7 +396,7 @@
   // Initialize thread 0.
   int tid = ThreadCreate(thr, 0, 0, true);
   CHECK_EQ(tid, 0);
-  ThreadStart(thr, tid, GetTid(), /*workerthread*/ false);
+  ThreadStart(thr, tid, GetTid(), ThreadType::Regular);
 #if TSAN_CONTAINS_UBSAN
   __ubsan::InitAsPlugin();
 #endif
Index: lib/tsan/rtl/tsan_rtl_report.cc
===================================================================
--- lib/tsan/rtl/tsan_rtl_report.cc
+++ lib/tsan/rtl/tsan_rtl_report.cc
@@ -201,7 +201,7 @@
   rt->running = (tctx->status == ThreadStatusRunning);
   rt->name = internal_strdup(tctx->name);
   rt->parent_tid = tctx->parent_tid;
-  rt->workerthread = tctx->workerthread;
+  rt->thread_type = tctx->thread_type;
   rt->stack = 0;
   rt->stack = SymbolizeStackId(tctx->creation_stack_id);
   if (rt->stack)
Index: lib/tsan/rtl/tsan_rtl_thread.cc
===================================================================
--- lib/tsan/rtl/tsan_rtl_thread.cc
+++ lib/tsan/rtl/tsan_rtl_thread.cc
@@ -239,7 +239,8 @@
   return tid;
 }
 
-void ThreadStart(ThreadState *thr, int tid, tid_t os_id, bool workerthread) {
+void ThreadStart(ThreadState *thr, int tid, tid_t os_id,
+                 ThreadType thread_type) {
   uptr stk_addr = 0;
   uptr stk_size = 0;
   uptr tls_addr = 0;
@@ -257,7 +258,7 @@
 
   ThreadRegistry *tr = ctx->thread_registry;
   OnStartedArgs args = { thr, stk_addr, stk_size, tls_addr, tls_size };
-  tr->StartThread(tid, os_id, workerthread, &args);
+  tr->StartThread(tid, os_id, thread_type, &args);
 
   tr->Lock();
   thr->tctx = (ThreadContext*)tr->GetThreadLocked(tid);