pitrou commented on a change in pull request #12358:
URL: https://github.com/apache/arrow/pull/12358#discussion_r801426885
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File path: cpp/src/arrow/util/thread_pool.cc
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@@ -235,24 +236,28 @@ 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();
-
- // Launch worker threads anew
- if (!state_->please_shutdown_) {
- ARROW_UNUSED(SetCapacity(capacity));
+ if (pid_.load() != current_pid) {
+ // Reinitialize internal state in child process after fork().
+ {
+ // Since after-fork reinitialization is triggered when one of the
ThreadPool
+ // methods is called, it can be very well be called from multiple threads
+ // at once. Therefore, it needs to be guarded with a lock.
+ auto lock = util::GlobalForkSafeMutex()->Lock();
Review comment:
You need a `std::call_once` per use case, though, while this lock is
global.
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