[libc-commits] [libc] 379428c - [libc] Linux threads - store a ptr to the thread attribs in the start args.

[Siva Chandra Reddy via libc-commits]

Author: Siva Chandra Reddy
Date: 2022-07-10T05:02:45Z
New Revision: 379428c2ac42fd3bd9bd2bf39f226dd6438e72ff

URL: https://github.com/llvm/llvm-project/commit/379428c2ac42fd3bd9bd2bf39f226dd6438e72ff
DIFF: https://github.com/llvm/llvm-project/commit/379428c2ac42fd3bd9bd2bf39f226dd6438e72ff.diff

LOG: [libc] Linux threads - store a ptr to the thread attribs in the start args.

Previosly, a pointer to the thread data structure was stored in the
start args. However, the thread data structure need not have the
lifetime of the thread. On the the other hand, thread attributes are
stored on the thread stack so they live as long as the thread lives.

Added: 
    

Modified: 
    libc/src/__support/threads/linux/thread.cpp

Removed: 
    


################################################################################
diff  --git a/libc/src/__support/threads/linux/thread.cpp b/libc/src/__support/threads/linux/thread.cpp
index fd0a3f69a7bd5..30c182045eeaf 100644
--- a/libc/src/__support/threads/linux/thread.cpp
+++ b/libc/src/__support/threads/linux/thread.cpp
@@ -75,7 +75,7 @@ struct Thread;
 // If 
diff erent architecture in future requires higher alignment, then we
 // can add a platform specific alignment spec.
 struct alignas(STACK_ALIGNMENT) StartArgs {
-  Thread *thread;
+  ThreadAttributes *thread_attrib;
   ThreadRunner runner;
   void *arg;
 };
@@ -101,8 +101,7 @@ __attribute__((always_inline)) inline uintptr_t get_start_args_addr() {
 
 static void start_thread() __attribute__((noinline)) {
   auto *start_args = reinterpret_cast<StartArgs *>(get_start_args_addr());
-  auto *thread = start_args->thread;
-  auto *attrib = thread->attrib;
+  auto *attrib = start_args->thread_attrib;
   long retval;
   if (attrib->style == ThreadStyle::POSIX) {
     attrib->retval.posix_retval =
@@ -115,11 +114,11 @@ static void start_thread() __attribute__((noinline)) {
   }
 
   uint32_t joinable_state = uint32_t(DetachState::JOINABLE);
-  if (!thread->attrib->detach_state.compare_exchange_strong(
+  if (!attrib->detach_state.compare_exchange_strong(
           joinable_state, uint32_t(DetachState::EXITING))) {
     // Thread is detached so cleanup the resources.
-    if (thread->attrib->owned_stack)
-      free_stack(thread->attrib->stack, thread->attrib->stack_size);
+    if (attrib->owned_stack)
+      free_stack(attrib->stack, attrib->stack_size);
   }
 
   __llvm_libc::syscall(SYS_exit, retval);
@@ -154,9 +153,6 @@ int Thread::run(ThreadStyle style, ThreadRunner runner, void *arg, void *stack,
   adjusted_stack &= ~(uintptr_t(STACK_ALIGNMENT) - 1);
 
   auto *start_args = reinterpret_cast<StartArgs *>(adjusted_stack);
-  start_args->thread = this;
-  start_args->runner = runner;
-  start_args->arg = arg;
 
   attrib =
       reinterpret_cast<ThreadAttributes *>(adjusted_stack + sizeof(StartArgs));
@@ -167,6 +163,10 @@ int Thread::run(ThreadStyle style, ThreadRunner runner, void *arg, void *stack,
   attrib->stack_size = size;
   attrib->owned_stack = owned_stack;
 
+  start_args->thread_attrib = attrib;
+  start_args->runner = runner;
+  start_args->arg = arg;
+
   auto clear_tid = reinterpret_cast<cpp::Atomic<FutexWordType> *>(
       adjusted_stack + sizeof(StartArgs) + sizeof(ThreadAttributes));
   clear_tid->val = CLEAR_TID_VALUE;