4 files changed, 24 insertions, 11 deletions
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 4dd3adda46ed..93039bf23f13 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -277,7 +277,7 @@ double NominalCPUFrequency() {
 #if defined(_WIN32)
 
 pid_t GetTID() {
-  return GetCurrentThreadId();
+  return pid_t{GetCurrentThreadId()};
 }
 
 #elif defined(__linux__)
diff --git a/absl/base/internal/sysinfo.h b/absl/base/internal/sysinfo.h
index b864a59741f1..93356d80d1c9 100644
--- a/absl/base/internal/sysinfo.h
+++ b/absl/base/internal/sysinfo.h
@@ -26,10 +26,10 @@
 
 #ifndef _WIN32
 #include <sys/types.h>
-#else
-#include <intsafe.h>
 #endif
 
+#include <cstdint>
+
 #include "absl/base/port.h"
 
 namespace absl {
@@ -51,9 +51,10 @@ int NumCPUs();
 // On Linux, you may send a signal to the resulting ID with kill().  However,
 // it is recommended for portability that you use pthread_kill() instead.
 #ifdef _WIN32
-// On Windows, process id and thread id are of the same type according to
-// the return types of GetProcessId() and GetThreadId() are both DWORD.
-using pid_t = DWORD;
+// On Windows, process id and thread id are of the same type according to the
+// return types of GetProcessId() and GetThreadId() are both DWORD, an unsigned
+// 32-bit type.
+using pid_t = uint32_t;
 #endif
 pid_t GetTID();
 
diff --git a/absl/base/internal/thread_identity.cc b/absl/base/internal/thread_identity.cc
index 91273a6b1a17..0ea159c58628 100644
--- a/absl/base/internal/thread_identity.cc
+++ b/absl/base/internal/thread_identity.cc
@@ -55,7 +55,12 @@ void AllocateThreadIdentityKey(ThreadIdentityReclaimerFunction reclaimer) {
 #ifdef __GNUC__
 __attribute__((visibility("protected")))
 #endif  // __GNUC__
-  ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity* thread_identity_ptr;
+#if ABSL_PER_THREAD_TLS
+// Prefer __thread to thread_local as benchmarks indicate it is a bit faster.
+ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity* thread_identity_ptr = nullptr;
+#elif defined(ABSL_HAVE_THREAD_LOCAL)
+thread_local ThreadIdentity* thread_identity_ptr = nullptr;
+#endif  // ABSL_PER_THREAD_TLS
 #endif  // TLS or CPP11
 
 void SetCurrentThreadIdentity(
@@ -69,8 +74,8 @@ void SetCurrentThreadIdentity(
   absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
                   reclaimer);
 
-#ifdef __EMSCRIPTEN__
-  // Emscripten PThread implementation does not support signals.
+#if defined(__EMSCRIPTEN__) || defined(__MINGW32__)
+  // Emscripten and MinGW pthread implementations does not support signals.
   // See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
   // for more information.
   pthread_setspecific(thread_identity_pthread_key,
@@ -89,7 +94,7 @@ void SetCurrentThreadIdentity(
   pthread_setspecific(thread_identity_pthread_key,
                       reinterpret_cast<void*>(identity));
   pthread_sigmask(SIG_SETMASK, &curr_signals, nullptr);
-#endif  // !__EMSCRIPTEN__
+#endif  // !__EMSCRIPTEN__ && !__MINGW32__
 
 #elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS
   // NOTE: Not async-safe.  But can be open-coded.
diff --git a/absl/base/internal/thread_identity.h b/absl/base/internal/thread_identity.h
index b34674a62d4b..7cbce9cc8e02 100644
--- a/absl/base/internal/thread_identity.h
+++ b/absl/base/internal/thread_identity.h
@@ -224,7 +224,14 @@ void ClearCurrentThreadIdentity();
 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
     ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
 
-extern ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity* thread_identity_ptr;
+#if ABSL_PER_THREAD_TLS
+ABSL_CONST_INIT extern ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity*
+    thread_identity_ptr;
+#elif defined(ABSL_HAVE_THREAD_LOCAL)
+ABSL_CONST_INIT extern thread_local ThreadIdentity* thread_identity_ptr;
+#else
+#error Thread-local storage not detected on this platform
+#endif
 
 inline ThreadIdentity* CurrentThreadIdentityIfPresent() {
   return thread_identity_ptr;