fix(core): fix nr_threads is zero

GitOrigin-RevId: 0ccbe3c69b5e94afe2068700252c23fca57ac910

dnn/test/common/utils.h

@@ -102,7 +102,7 @@ class CpuDispatchChecker final : MegcoreCPUDispatcher {
         std::vector<std::thread> m_workers;
 #endif
         //! Total number of threads, including main thread.
-        size_t m_nr_threads = 0;
+        size_t m_nr_threads = 1;
     };
 
     //! track number of CpuDispatchChecker instances to avoid leaking

src/core/impl/utils/thread_pool.cpp

@@ -20,6 +20,9 @@ ThreadPool::ThreadPool(size_t threads_num)
           m_main_affinity_flag{false},
           m_stop{false},
           m_active{false} {
+    if (threads_num < 1) {
+        m_nr_threads = 1;
+    }
     if (m_nr_threads > 1) {
         if (m_nr_threads > static_cast<uint32_t>(sys::get_cpu_count())) {
             mgb_log_debug(

src/core/include/megbrain/utils/thread_pool.h

@@ -80,7 +80,7 @@ public:
     ~ThreadPool();
 
 private:
-    const size_t m_nr_threads = 0;
+    size_t m_nr_threads = 1;
     //! Indicate whether the main thread have binding
     bool m_main_affinity_flag;
     //! The callback binding the threads to cores