[libc-commits] [libc] [libc] Apply scheduler attributes on thread creation (PR #225674)

[Pavel Labath via libc-commits]

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@@ -150,9 +151,29 @@ cleanup_thread_resources(ThreadAttributes *attrib) {
     free_stack(attrib->stack, attrib->stacksize, attrib->guardsize);
 }
 
+// Enum values used for controlling thread startup.
+enum class ClearTidState : FutexWordType {
+  EXITED = 0, // Set by the kernel when the thread exits.
+  WAITING,    // Waiting for additional initialization.
+  RUNNING,    // Initialization complete or not needed.
+  ABORT,      // Initialization failed.
+};
+
 static int start_thread(void *arg) {
   auto *start_args = reinterpret_cast<StartArgs *>(arg);
   auto *attrib = start_args->thread_attrib;
+  auto *clear_tid = static_cast<Futex *>(attrib->platform_data);
+
+  // If explicit scheduling parameters were requested, wait for the parent to
+  // apply them via setschedparam. If setschedparam fails, the parent signals
+  // ABORT, and the child exits immediately without running user code.
+  clear_tid->wait(static_cast<FutexWordType>(ClearTidState::WAITING),
+                  cpp::nullopt, /*is_shared=*/false);
+  if (clear_tid->load(cpp::MemoryOrder::ACQUIRE) ==
+      static_cast<FutexWordType>(ClearTidState::ABORT)) {
+    LIBC_NAMESPACE::syscall_impl<long>(SYS_exit, 0);
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labath wrote:

Done.

https://github.com/llvm/llvm-project/pull/225674