Replace after-fork-use DFATAL with ERROR

Differential Revision: D25683616

fbshipit-source-id: 7f199b0e43e0a5a76c4cf16412b22abdc28833ac

folly/Singleton-inl.h

@@ -174,8 +174,13 @@ template <typename T>
 void SingletonHolder<T>::destroyInstance() {
   if (state_.load(std::memory_order_relaxed) ==
       SingletonHolderState::LivingInChildAfterFork) {
-    LOG(DFATAL) << "Attempting to destroy singleton " << type().name()
-                << " in child process after fork";
+    if (vault_.failOnUseAfterFork_) {
+      LOG(DFATAL) << "Attempting to destroy singleton " << type().name()
+                  << " in child process after fork";
+    } else {
+      LOG(ERROR) << "Attempting to destroy singleton " << type().name()
+                 << " in child process after fork";
+    }
   }
   state_ = SingletonHolderState::Dead;
   instance_.reset();
@@ -242,8 +247,13 @@ void SingletonHolder<T>::createInstance() {
   }
   if (state_.load(std::memory_order_relaxed) ==
       SingletonHolderState::LivingInChildAfterFork) {
-    LOG(DFATAL) << "Attempting to use singleton " << type().name()
-                << " in child process after fork";
+    if (vault_.failOnUseAfterFork_) {
+      LOG(DFATAL) << "Attempting to use singleton " << type().name()
+                  << " in child process after fork";
+    } else {
+      LOG(ERROR) << "Attempting to use singleton " << type().name()
+                 << " in child process after fork";
+    }
     auto expected = SingletonHolderState::LivingInChildAfterFork;
     state_.compare_exchange_strong(
         expected,

folly/Singleton.h

@@ -522,6 +522,10 @@ class SingletonVault {
 
   [[noreturn]] void fireShutdownTimer();
 
+  void setFailOnUseAfterFork(bool failOnUseAfterFork) {
+    failOnUseAfterFork_ = failOnUseAfterFork;
+  }
+
  private:
   template <typename T>
   friend struct detail::SingletonHolder;
@@ -567,6 +571,7 @@ class SingletonVault {
   std::atomic<bool> shutdownTimerStarted_{false};
   std::chrono::milliseconds shutdownTimeout_{std::chrono::minutes{5}};
   Synchronized<std::vector<std::string>> shutdownLog_;
+  bool failOnUseAfterFork_{false};
 };
 
 // This is the wrapper class that most users actually interact with.

folly/test/SingletonTest.cpp

@@ -1069,6 +1069,7 @@ TEST(Singleton, ForkInChild) {
   using SingletonObject = Singleton<ForkObject, PrivateTag, VaultTag>;
 
   auto& vault = *SingletonVault::singleton<VaultTag>();
+  vault.setFailOnUseAfterFork(true);
   SingletonObject object;
   vault.registrationComplete();