fix perfermance degradation in photon::thread_create (alibaba#1043) (alibaba#1046)

Signed-off-by: ivanallen <ivan_allen@163.com>

Author: ivanallen

thread/thread.cpp

@@ -976,7 +976,8 @@ R"(
         RunQ rq;
         if (unlikely(!rq.current))
             LOG_ERROR_RETURN(ENOSYS, nullptr, "Photon not initialized in this vCPU (OS thread)");
-        size_t randomizer = (rand() % 512) * 8;
+        thread_local uint64_t random_index = 0;
+        size_t randomizer = (random_index++ % 512) * 8;
         // stack contains struct, randomizer space, and reserved_space
         size_t least_stack_size = sizeof(thread) + randomizer + 63 + reserved_space;
         // at least a whole page for mprotect