[GitHub] [incubator-brpc] SF-Zhou opened a new pull request #1358: Fix deadlock in TaskGroup::push_rq

[GitBox <gi...@apache.org>]

SF-Zhou opened a new pull request #1358:
URL: https://github.com/apache/incubator-brpc/pull/1358


   This is a known bug in src/bthread/task_group_inl.h. It will cause a deadlock when all workers are spinning in `TaskGroup::push_rq`. A reproducible code:
   ```c++
   #include <bthread/bthread.h>
   
   static std::atomic<size_t> value{0};
   
   void* do_job(void*) {
     ++value;
     return nullptr;
   }
   
   void* start(void*) {
     const uint32_t M = 10000;  // bigger than default queue capacity
     std::vector<bthread_t> tids(M);
     for (auto& tid : tids) {
       bthread_start_background(&tid, &BTHREAD_ATTR_SMALL, do_job, nullptr);
     }
     for (auto& tid : tids) {
       bthread_join(tid, nullptr);
     }
     return nullptr;
   }
   
   int main(int argc, char* argv[]) {
     const uint32_t N = 10;  // bigger than default concurrency
   
     std::vector<bthread_t> tids(N);
     for (auto& tid : tids) {
       bthread_start_urgent(&tid, &BTHREAD_ATTR_SMALL, start, nullptr);
     }
     for (auto& tid : tids) {
       bthread_join(tid, nullptr);
     }
     printf("Value = %lu\n", value.load());
     return 0;
   }
   ```


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