[GitHub] [arrow] pitrou commented on a change in pull request #12350: ARROW-15593: [C++] Fix a race condition in the thread pool

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

pitrou commented on a change in pull request #12350:
URL: https://github.com/apache/arrow/pull/12350#discussion_r800744882



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File path: cpp/src/arrow/util/thread_pool.cc
##########
@@ -235,23 +235,32 @@ ThreadPool::~ThreadPool() {
 void ThreadPool::ProtectAgainstFork() {
 #ifndef _WIN32
   pid_t current_pid = getpid();
-  if (pid_ != current_pid) {
-    // Reinitialize internal state in child process after fork()
-    // Ideally we would use pthread_at_fork(), but that doesn't allow
-    // storing an argument, hence we'd need to maintain a list of all
-    // existing ThreadPools.
-    int capacity = state_->desired_capacity_;
-
-    auto new_state = std::make_shared<ThreadPool::State>();
-    new_state->please_shutdown_ = state_->please_shutdown_;
-    new_state->quick_shutdown_ = state_->quick_shutdown_;
-
-    pid_ = current_pid;
-    sp_state_ = new_state;
-    state_ = sp_state_.get();
-
+  pid_t old_pid = pid_.load();
+  int capacity = 0;
+  if (current_pid != old_pid) {
+    // FIXME: It may get deadlock here if users fork processes while the parent runs
+    // in the middle of resetting states.

Review comment:
       FTR, I'm working on a better fix for this.




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