Add a termination tag to the blocking context

Summary:
Add a termination tag that carries through the blocking context chain. This flag notifies logging operations that they may go as far as to terminate the process if blocking operations are detected.

The flags carry through the blocking scopes so the termination flag will stay present while we enable and disable blocking - it would be sticky for a given thread once set.

Reviewed By: yfeldblum

Differential Revision: D27869075

fbshipit-source-id: 27014a3e6c9b28c0f433949a576bb6116e7c06c0

folly/Executor.cpp

@@ -51,35 +51,56 @@ void Executor::keepAliveRelease() noexcept {
              << "which do not override keepAliveAcquire()";
 }
 
+// Base case of permitting with no termination to avoid nullptr tests
+static ExecutorBlockingList emptyList{nullptr, {false, false, {}}};
+
 #if defined(FOLLY_TLS)
 
 extern constexpr bool const executor_blocking_list_enabled = true;
-thread_local ExecutorBlockingList* executor_blocking_list = nullptr;
+thread_local ExecutorBlockingList* executor_blocking_list = &emptyList;
 
 #else
 
 extern constexpr bool const executor_blocking_list_enabled = false;
-ExecutorBlockingList* executor_blocking_list = nullptr;
+ExecutorBlockingList* executor_blocking_list = &emptyList;
 
 #endif
 
 Optional<ExecutorBlockingContext> getExecutorBlockingContext() noexcept {
   return //
-      !executor_blocking_list || !executor_blocking_list->forbid ? none : //
+      !executor_blocking_list->curr.forbid ? none : //
       make_optional(executor_blocking_list->curr);
 }
 
 ExecutorBlockingGuard::ExecutorBlockingGuard(PermitTag) noexcept
-    : list_{false, executor_blocking_list, {}} {
+    : list_{*executor_blocking_list} {
   if (executor_blocking_list_enabled) {
+    list_.prev = executor_blocking_list;
+    list_.curr.forbid = false;
+    list_.curr.name = {};
     executor_blocking_list = &list_;
   }
 }
 
 ExecutorBlockingGuard::ExecutorBlockingGuard(
     TrackTag, StringPiece name) noexcept
-    : list_{true, executor_blocking_list, {name}} {
+    : list_{*executor_blocking_list} {
+  if (executor_blocking_list_enabled) {
+    list_.prev = executor_blocking_list;
+    list_.curr.forbid = true;
+    list_.curr.name = name;
+    executor_blocking_list = &list_;
+  }
+}
+
+ExecutorBlockingGuard::ExecutorBlockingGuard(
+    ProhibitTag, StringPiece name) noexcept
+    : list_{*executor_blocking_list} {
   if (executor_blocking_list_enabled) {
+    list_.prev = executor_blocking_list;
+    list_.curr.forbid = true;
+    list_.curr.allowTerminationOnBlocking = true;
+    list_.curr.name = name;
     executor_blocking_list = &list_;
   }
 }

folly/Executor.h

@@ -307,6 +307,8 @@ Executor::KeepAlive<ExecutorT> getKeepAliveToken(
 }
 
 struct ExecutorBlockingContext {
+  bool forbid;
+  bool allowTerminationOnBlocking;
   StringPiece name;
 };
 static_assert(
@@ -314,7 +316,6 @@ static_assert(
     "non-standard layout");
 
 struct ExecutorBlockingList {
-  bool forbid;
   ExecutorBlockingList* prev;
   ExecutorBlockingContext curr;
 };
@@ -326,12 +327,14 @@ class ExecutorBlockingGuard {
  public:
   struct PermitTag {};
   struct TrackTag {};
+  struct ProhibitTag {};
 
   ~ExecutorBlockingGuard();
   ExecutorBlockingGuard() = delete;
 
   explicit ExecutorBlockingGuard(PermitTag) noexcept;
   explicit ExecutorBlockingGuard(TrackTag, StringPiece name) noexcept;
+  explicit ExecutorBlockingGuard(ProhibitTag, StringPiece name) noexcept;
 
   ExecutorBlockingGuard(ExecutorBlockingGuard&&) = delete;
   ExecutorBlockingGuard(ExecutorBlockingGuard const&) = delete;