fix: Remove race condition in memory allocator initialization

[yurekami]

Summary

• Fixes Potential Race Condition in Memory Allocator Initialization #315: Potential Race Condition in Memory Allocator Initialization
• Removes the unsynchronized gAllocatorInited flag that caused a race condition
• Relies solely on std::call_once which provides proper thread-safety guarantees

Problem

The original code had a race condition in GlobalMemoryAllocator.cc:

static bool gAllocatorInited = false;  // Plain bool, not atomic

void *allocate(size_t size) {
  if (!gAllocatorInited) {  // Multiple threads can pass this check
    std::call_once(gInitOnce, loadMemoryAllocatorLib);
    gAllocatorInited = true;  // Can be reordered with gAllocator write
  }

Issues:

1. gAllocatorInited is a plain bool, not atomic - no synchronization
2. Instruction reordering: gAllocatorInited = true can execute before std::call_once fully completes
3. Memory visibility: other threads may see gAllocatorInited = true while gAllocator is still uninitialized

Solution

Remove the redundant flag and rely solely on std::call_once:

void *allocate(size_t size) {
  std::call_once(gInitOnce, loadMemoryAllocatorLib);

Why this works:

• std::call_once provides full happens-before guarantees (C++11 standard)
• After first execution, call_once becomes a fast single atomic load (efficient fast-path)
• No performance degradation - simpler code with same or better performance

Test plan

• Verify existing unit tests pass
• Code review for thread-safety correctness
• The fix is minimal and follows the principle of relying on well-tested standard library primitives

🤖 Generated with Claude Code