Generalize pthread TLS to any trivial type (#27009)

* Avoid copy constructor

```
src/core/lib/gpr/log_linux.cc:78:33: error: copying variable of type 'grpc_core::PthreadTlsImpl<long>' invokes deleted constructor
  static GPR_THREAD_LOCAL(long) tid = 0;
                                ^     ~
./src/core/lib/gpr/tls.h:64:3: note: 'PthreadTlsImpl' has been explicitly marked deleted here
  PthreadTlsImpl(const PthreadTlsImpl&) = delete;
  ^
1 error generated.
```

* Generalize pthread TLS to any trivial type

Use multiple pthread keys for types larger than a machine word.

Implement generic timer TLS optimization on all platforms.

CMakeLists.txt

@@ -718,7 +718,6 @@ if(gRPC_BUILD_TESTS)
   add_dependencies(buildtests_c timeout_encoding_test)
   add_dependencies(buildtests_c timer_heap_test)
   add_dependencies(buildtests_c timer_list_test)
-  add_dependencies(buildtests_c tls_test)
   add_dependencies(buildtests_c transport_security_common_api_test)
   add_dependencies(buildtests_c transport_security_test)
   if(_gRPC_PLATFORM_LINUX OR _gRPC_PLATFORM_MAC OR _gRPC_PLATFORM_POSIX)
@@ -1001,6 +1000,7 @@ if(gRPC_BUILD_TESTS)
   add_dependencies(buildtests_cxx time_util_test)
   add_dependencies(buildtests_cxx timer_test)
   add_dependencies(buildtests_cxx tls_security_connector_test)
+  add_dependencies(buildtests_cxx tls_test)
   add_dependencies(buildtests_cxx too_many_pings_test)
   add_dependencies(buildtests_cxx transport_stream_receiver_test)
   add_dependencies(buildtests_cxx try_join_test)
@@ -7537,33 +7537,6 @@ target_link_libraries(timer_list_test
 )
 
 
-endif()
-if(gRPC_BUILD_TESTS)
-
-add_executable(tls_test
-  test/core/gpr/tls_test.cc
-)
-
-target_include_directories(tls_test
-  PRIVATE
-    ${CMAKE_CURRENT_SOURCE_DIR}
-    ${CMAKE_CURRENT_SOURCE_DIR}/include
-    ${_gRPC_ADDRESS_SORTING_INCLUDE_DIR}
-    ${_gRPC_RE2_INCLUDE_DIR}
-    ${_gRPC_SSL_INCLUDE_DIR}
-    ${_gRPC_UPB_GENERATED_DIR}
-    ${_gRPC_UPB_GRPC_GENERATED_DIR}
-    ${_gRPC_UPB_INCLUDE_DIR}
-    ${_gRPC_XXHASH_INCLUDE_DIR}
-    ${_gRPC_ZLIB_INCLUDE_DIR}
-)
-
-target_link_libraries(tls_test
-  ${_gRPC_ALLTARGETS_LIBRARIES}
-  grpc_test_util
-)
-
-
 endif()
 if(gRPC_BUILD_TESTS)
 
@@ -15836,6 +15809,41 @@ target_link_libraries(tls_security_connector_test
 )
 
 
+endif()
+if(gRPC_BUILD_TESTS)
+
+add_executable(tls_test
+  test/core/gpr/tls_test.cc
+  third_party/googletest/googletest/src/gtest-all.cc
+  third_party/googletest/googlemock/src/gmock-all.cc
+)
+
+target_include_directories(tls_test
+  PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+    ${_gRPC_ADDRESS_SORTING_INCLUDE_DIR}
+    ${_gRPC_RE2_INCLUDE_DIR}
+    ${_gRPC_SSL_INCLUDE_DIR}
+    ${_gRPC_UPB_GENERATED_DIR}
+    ${_gRPC_UPB_GRPC_GENERATED_DIR}
+    ${_gRPC_UPB_INCLUDE_DIR}
+    ${_gRPC_XXHASH_INCLUDE_DIR}
+    ${_gRPC_ZLIB_INCLUDE_DIR}
+    third_party/googletest/googletest/include
+    third_party/googletest/googletest
+    third_party/googletest/googlemock/include
+    third_party/googletest/googlemock
+    ${_gRPC_PROTO_GENS_DIR}
+)
+
+target_link_libraries(tls_test
+  ${_gRPC_PROTOBUF_LIBRARIES}
+  ${_gRPC_ALLTARGETS_LIBRARIES}
+  grpc_test_util
+)
+
+
 endif()
 if(gRPC_BUILD_TESTS)
 

build_autogenerated.yaml

@@ -4151,15 +4151,6 @@ targets:
   deps:
   - grpc_test_util
   uses_polling: false
-- name: tls_test
-  build: test
-  language: c
-  headers: []
-  src:
-  - test/core/gpr/tls_test.cc
-  deps:
-  - grpc_test_util
-  uses_polling: false
 - name: transport_security_common_api_test
   build: test
   language: c
@@ -7440,6 +7431,16 @@ targets:
   - test/core/security/tls_security_connector_test.cc
   deps:
   - grpc_test_util
+- name: tls_test
+  gtest: true
+  build: test
+  language: c++
+  headers: []
+  src:
+  - test/core/gpr/tls_test.cc
+  deps:
+  - grpc_test_util
+  uses_polling: false
 - name: too_many_pings_test
   gtest: true
   build: test

src/core/lib/gpr/log_linux.cc

@@ -75,7 +75,7 @@ void gpr_default_log(gpr_log_func_args* args) {
   time_t timer;
   gpr_timespec now = gpr_now(GPR_CLOCK_REALTIME);
   struct tm tm;
-  static GPR_THREAD_LOCAL(long) tid = 0;
+  static GPR_THREAD_LOCAL(long) tid(0);
   if (tid == 0) tid = sys_gettid();
 
   timer = static_cast<time_t>(now.tv_sec);

src/core/lib/gpr/tls.h

@@ -35,15 +35,10 @@ namespace grpc_core {
 // This class is never instantiated. It exists to statically ensure that all
 // TLS usage is compatible with the most restrictive implementation, allowing
 // developers to write correct code regardless of the platform they develop on.
-template <typename T, typename = typename std::enable_if<(
-                          std::is_trivially_destructible<T>::value &&
-                          sizeof(T) <= sizeof(void*) &&
-                          alignof(void*) % alignof(T) == 0)>::type>
+template <typename T>
 class TlsTypeConstrainer {
-  static_assert(std::is_trivially_destructible<T>::value &&
-                    sizeof(T) <= sizeof(void*) &&
-                    alignof(void*) % alignof(T) == 0,
-                "unsupported type for TLS");
+  static_assert(std::is_trivial<T>::value,
+                "TLS support is limited to trivial types");
 
  public:
   using Type = T;
@@ -55,6 +50,8 @@ class TlsTypeConstrainer {
 
 #include <grpc/support/log.h> /* for GPR_ASSERT */
 #include <pthread.h>
+#include <array>
+#include <cstring>
 
 namespace grpc_core {
 
@@ -91,50 +88,51 @@ class PthreadTlsImpl : TlsTypeConstrainer<T> {
   //
   // https://google.github.io/styleguide/cppguide.html#Static_and_Global_Variables
   PthreadTlsImpl()
-      : key_([]() {
-          pthread_key_t key;
-          GPR_ASSERT(0 == pthread_key_create(&key, nullptr));
-          return key;
+      : keys_([]() {
+          typename std::remove_const<decltype(PthreadTlsImpl::keys_)>::type
+              keys;
+          for (pthread_key_t& key : keys) {
+            GPR_ASSERT(0 == pthread_key_create(&key, nullptr));
+          }
+          return keys;
         }()) {}
   PthreadTlsImpl(T t) : PthreadTlsImpl() { *this = t; }
-  ~PthreadTlsImpl() { GPR_ASSERT(0 == pthread_key_delete(key_)); }
-
-  operator T() const { return Cast<T>(pthread_getspecific(key_)); }
-
-  T operator=(T t) {
-    GPR_ASSERT(0 == pthread_setspecific(key_, Cast<T>(t)));
-    return t;
+  ~PthreadTlsImpl() {
+    for (pthread_key_t key : keys_) {
+      GPR_ASSERT(0 == pthread_key_delete(key));
+    }
   }
 
- private:
-  // TODO(C++17): Replace these helpers with constexpr if statements inline.
-  template <typename V>
-  static typename std::enable_if<std::is_pointer<V>::value, V>::type Cast(
-      void* object) {
-    return static_cast<V>(object);
-  }
-
-  template <typename V>
-  static typename std::enable_if<
-      !std::is_pointer<V>::value && std::is_integral<V>::value, V>::type
-  Cast(void* object) {
-    return reinterpret_cast<uintptr_t>(object);
-  }
-
-  template <typename V>
-  static void* Cast(
-      typename std::enable_if<std::is_pointer<V>::value, V>::type t) {
+  operator T() const {
+    T t;
+    char* dst = reinterpret_cast<char*>(&t);
+    for (pthread_key_t key : keys_) {
+      uintptr_t src = uintptr_t(pthread_getspecific(key));
+      size_t remaining = reinterpret_cast<char*>(&t + 1) - dst;
+      size_t step = std::min(sizeof(src), remaining);
+      memcpy(dst, &src, step);
+      dst += step;
+    }
     return t;
   }
 
-  template <typename V>
-  static void* Cast(typename std::enable_if<!std::is_pointer<V>::value &&
-                                                std::is_integral<V>::value,
-                                            V>::type t) {
-    return reinterpret_cast<void*>(uintptr_t(t));
+  T operator=(T t) {
+    char* src = reinterpret_cast<char*>(&t);
+    for (pthread_key_t key : keys_) {
+      uintptr_t dst;
+      size_t remaining = reinterpret_cast<char*>(&t + 1) - src;
+      size_t step = std::min(sizeof(dst), remaining);
+      memcpy(&dst, src, step);
+      GPR_ASSERT(0 == pthread_setspecific(key, reinterpret_cast<void*>(dst)));
+      src += step;
+    }
+    return t;
   }
 
-  const pthread_key_t key_;
+ private:
+  const std::array<pthread_key_t,
+                   (sizeof(T) + sizeof(void*) - 1) / sizeof(void*)>
+      keys_;
 };
 
 }  // namespace grpc_core

src/core/lib/iomgr/timer_generic.cc

@@ -212,19 +212,11 @@ static void validate_non_pending_timer(grpc_timer* t) {
 
 #endif
 
-#if GPR_ARCH_64
-/* NOTE: TODO(sreek) - Currently the thread local storage support in grpc is
-   for intptr_t which means on 32-bit machines it is not wide enough to hold
-   grpc_millis which is 64-bit. Adding thread local support for 64 bit values
-   is a lot of work for very little gain. So we are currently restricting this
-   optimization to only 64 bit machines */
-
 /* Thread local variable that stores the deadline of the next timer the thread
  * has last-seen. This is an optimization to prevent the thread from checking
  * shared_mutables.min_timer (which requires acquiring shared_mutables.mu lock,
  * an expensive operation) */
 static GPR_THREAD_LOCAL(grpc_millis) g_last_seen_min_timer;
-#endif
 
 struct shared_mutables {
   /* The deadline of the next timer due across all timer shards */
@@ -269,10 +261,7 @@ static void timer_list_init() {
   gpr_mu_init(&g_shared_mutables.mu);
   g_shared_mutables.min_timer = grpc_core::ExecCtx::Get()->Now();
 
-#if GPR_ARCH_64
-
   g_last_seen_min_timer = 0;
-#endif
 
   for (i = 0; i < g_num_shards; i++) {
     timer_shard* shard = &g_shards[i];
@@ -301,11 +290,6 @@ static void timer_list_shutdown() {
     grpc_timer_heap_destroy(&shard->heap);
   }
   gpr_mu_destroy(&g_shared_mutables.mu);
-
-#if GPR_ARCH_64
-
-#endif
-
   gpr_free(g_shards);
   gpr_free(g_shard_queue);
   g_shared_mutables.initialized = false;
@@ -452,10 +436,8 @@ static void timer_init(grpc_timer* timer, grpc_millis deadline,
 }
 
 static void timer_consume_kick(void) {
-#if GPR_ARCH_64
   /* Force re-evaluation of last seen min */
   g_last_seen_min_timer = 0;
-#endif
 }
 
 static void timer_cancel(grpc_timer* timer) {
@@ -592,7 +574,6 @@ static grpc_timer_check_result run_some_expired_timers(
   // safe since we know that both are pointer types and 64-bit wide
   grpc_millis min_timer = static_cast<grpc_millis>(
       gpr_atm_no_barrier_load((gpr_atm*)(&g_shared_mutables.min_timer)));
-  g_last_seen_min_timer = min_timer;
 #else
   // On 32-bit systems, gpr_atm_no_barrier_load does not work on 64-bit types
   // (like grpc_millis). So all reads and writes to g_shared_mutables.min_timer
@@ -601,6 +582,8 @@ static grpc_timer_check_result run_some_expired_timers(
   grpc_millis min_timer = g_shared_mutables.min_timer;
   gpr_mu_unlock(&g_shared_mutables.mu);
 #endif
+  g_last_seen_min_timer = min_timer;
+
   if (now < min_timer) {
     if (next != nullptr) *next = GPR_MIN(*next, min_timer);
     return GRPC_TIMERS_CHECKED_AND_EMPTY;
@@ -676,20 +659,9 @@ static grpc_timer_check_result timer_check(grpc_millis* next) {
   // prelude
   grpc_millis now = grpc_core::ExecCtx::Get()->Now();
 
-#if GPR_ARCH_64
   /* fetch from a thread-local first: this avoids contention on a globally
      mutable cacheline in the common case */
   grpc_millis min_timer = g_last_seen_min_timer;
-#else
-  // On 32-bit systems, we currently do not have thread local support for 64-bit
-  // types. In this case, directly read from g_shared_mutables.min_timer.
-  // Also, note that on 32-bit systems, gpr_atm_no_barrier_store does not work
-  // on 64-bit types (like grpc_millis). So all reads and writes to
-  // g_shared_mutables.min_timer are done under g_shared_mutables.mu
-  gpr_mu_lock(&g_shared_mutables.mu);
-  grpc_millis min_timer = g_shared_mutables.min_timer;
-  gpr_mu_unlock(&g_shared_mutables.mu);
-#endif
 
   if (now < min_timer) {
     if (next != nullptr) {

test/core/gpr/BUILD

@@ -134,6 +134,9 @@ grpc_cc_test(
 grpc_cc_test(
     name = "tls_test",
     srcs = ["tls_test.cc"],
+    external_deps = [
+        "gtest",
+    ],
     language = "C++",
     uses_polling = False,
     deps = [

test/core/gpr/tls_test.cc

@@ -20,45 +20,47 @@
 
 #include "src/core/lib/gpr/tls.h"
 
-#include <stdio.h>
-#include <stdlib.h>
-
-#include <grpc/support/log.h>
-#include <grpc/support/sync.h>
+#include <gtest/gtest.h>
+#include <array>
 
 #include "src/core/lib/gprpp/thd.h"
 #include "test/core/util/test_config.h"
 
-#define NUM_THREADS 100
-
-static GPR_THREAD_LOCAL(intptr_t) test_var;
-
-static void thd_body(void* /*arg*/) {
-  intptr_t i;
+struct BiggerThanMachineWord {
+  size_t a, b;
+  uint8_t c;
+};
 
-  GPR_ASSERT(test_var == 0);
+static GPR_THREAD_LOCAL(BiggerThanMachineWord) test_var;
+// Fails to compile: static GPR_THREAD_LOCAL(std::unique_ptr<char>) non_trivial;
 
-  for (i = 0; i < 100000; i++) {
-    test_var = i;
-    GPR_ASSERT(test_var == i);
+namespace {
+void thd_body(void*) {
+  for (size_t i = 0; i < 100000; i++) {
+    BiggerThanMachineWord next = {i, i, uint8_t(i)};
+    test_var = next;
+    BiggerThanMachineWord read = test_var;
+    ASSERT_EQ(read.a, i);
+    ASSERT_EQ(read.b, i);
+    ASSERT_EQ(read.c, uint8_t(i)) << i;
   }
-  test_var = 0;
 }
 
-/* ------------------------------------------------- */
-
-int main(int argc, char* argv[]) {
-  grpc_core::Thread threads[NUM_THREADS];
-
-  grpc::testing::TestEnvironment env(argc, argv);
-
-  for (auto& th : threads) {
+TEST(ThreadLocal, ReadWrite) {
+  std::array<grpc_core::Thread, 100> threads;
+  for (grpc_core::Thread& th : threads) {
     th = grpc_core::Thread("grpc_tls_test", thd_body, nullptr);
     th.Start();
   }
-  for (auto& th : threads) {
+  for (grpc_core::Thread& th : threads) {
     th.Join();
   }
+}
 
-  return 0;
+}  // namespace
+
+int main(int argc, char* argv[]) {
+  grpc::testing::TestEnvironment env(argc, argv);
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
 }

tools/run_tests/generated/tests.json

@@ -2939,30 +2939,6 @@
     ],
     "uses_polling": false
   },
-  {
-    "args": [],
-    "benchmark": false,
-    "ci_platforms": [
-      "linux",
-      "mac",
-      "posix",
-      "windows"
-    ],
-    "cpu_cost": 1.0,
-    "exclude_configs": [],
-    "exclude_iomgrs": [],
-    "flaky": false,
-    "gtest": false,
-    "language": "c",
-    "name": "tls_test",
-    "platforms": [
-      "linux",
-      "mac",
-      "posix",
-      "windows"
-    ],
-    "uses_polling": false
-  },
   {
     "args": [],
     "benchmark": false,
@@ -7081,6 +7057,30 @@
     ],
     "uses_polling": true
   },
+  {
+    "args": [],
+    "benchmark": false,
+    "ci_platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "cpu_cost": 1.0,
+    "exclude_configs": [],
+    "exclude_iomgrs": [],
+    "flaky": false,
+    "gtest": true,
+    "language": "c++",
+    "name": "tls_test",
+    "platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "uses_polling": false
+  },
   {
     "args": [],
     "benchmark": false,