Implement a better GetTID on Apple platforms, and a better fallback too.
The fallback isn't totally portable, even within POSIX, but we can special case any future platforms where it's not just like this change does for Apple.
PiperOrigin-RevId: 535324103
Change-Id: Ib628925c4946b6c112373678fe37e9bb44259090
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 8429fb9..ed20335 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -414,82 +414,24 @@
return tid;
}
+#elif defined(__APPLE__)
+
+pid_t GetTID() {
+ uint64_t tid;
+ // `nullptr` here implies this thread. This only fails if the specified
+ // thread is invalid or the pointer-to-tid is null, so we needn't worry about
+ // it.
+ pthread_threadid_np(nullptr, &tid);
+ return static_cast<pid_t>(tid);
+}
+
#else
-// Fallback implementation of GetTID using pthread_getspecific.
-ABSL_CONST_INIT static once_flag tid_once;
-ABSL_CONST_INIT static pthread_key_t tid_key;
-ABSL_CONST_INIT static absl::base_internal::SpinLock tid_lock(
- absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
-
-// We set a bit per thread in this array to indicate that an ID is in
-// use. ID 0 is unused because it is the default value returned by
-// pthread_getspecific().
-ABSL_CONST_INIT static std::vector<uint32_t> *tid_array
- ABSL_GUARDED_BY(tid_lock) = nullptr;
-static constexpr int kBitsPerWord = 32; // tid_array is uint32_t.
-
-// Returns the TID to tid_array.
-static void FreeTID(void *v) {
- intptr_t tid = reinterpret_cast<intptr_t>(v);
- intptr_t word = tid / kBitsPerWord;
- uint32_t mask = ~(1u << (tid % kBitsPerWord));
- absl::base_internal::SpinLockHolder lock(&tid_lock);
- assert(0 <= word && static_cast<size_t>(word) < tid_array->size());
- (*tid_array)[static_cast<size_t>(word)] &= mask;
-}
-
-static void InitGetTID() {
- if (pthread_key_create(&tid_key, FreeTID) != 0) {
- // The logging system calls GetTID() so it can't be used here.
- perror("pthread_key_create failed");
- abort();
- }
-
- // Initialize tid_array.
- absl::base_internal::SpinLockHolder lock(&tid_lock);
- tid_array = new std::vector<uint32_t>(1);
- (*tid_array)[0] = 1; // ID 0 is never-allocated.
-}
-
-// Return a per-thread small integer ID from pthread's thread-specific data.
+// Fallback implementation of `GetTID` using `pthread_self`.
pid_t GetTID() {
- absl::call_once(tid_once, InitGetTID);
-
- intptr_t tid = reinterpret_cast<intptr_t>(pthread_getspecific(tid_key));
- if (tid != 0) {
- return static_cast<pid_t>(tid);
- }
-
- int bit; // tid_array[word] = 1u << bit;
- size_t word;
- {
- // Search for the first unused ID.
- absl::base_internal::SpinLockHolder lock(&tid_lock);
- // First search for a word in the array that is not all ones.
- word = 0;
- while (word < tid_array->size() && ~(*tid_array)[word] == 0) {
- ++word;
- }
- if (word == tid_array->size()) {
- tid_array->push_back(0); // No space left, add kBitsPerWord more IDs.
- }
- // Search for a zero bit in the word.
- bit = 0;
- while (bit < kBitsPerWord && (((*tid_array)[word] >> bit) & 1) != 0) {
- ++bit;
- }
- tid =
- static_cast<intptr_t>((word * kBitsPerWord) + static_cast<size_t>(bit));
- (*tid_array)[word] |= 1u << bit; // Mark the TID as allocated.
- }
-
- if (pthread_setspecific(tid_key, reinterpret_cast<void *>(tid)) != 0) {
- perror("pthread_setspecific failed");
- abort();
- }
-
- return static_cast<pid_t>(tid);
+ // `pthread_t` need not be arithmetic per POSIX; platforms where it isn't
+ // should be handled above.
+ return static_cast<pid_t>(pthread_self());
}
#endif
