Support gRPC Python client-side fork with epoll1

A process may fork after invoking grpc_init() and use gRPC in the child
if and only if the child process first destroys all gRPC resources
inherited from the parent process and invokes grpc_shutdown().
Subsequent to this, the child will be able to re-initialize and use
gRPC. After fork, the parent process will be able to continue to use
existing gRPC resources such as channels and calls without interference
from the child process.

To facilitate gRPC Python applications meeting the above constraints,
gRPC Python will automatically destroy and shutdown all gRPC Core
resources in the child's post-fork handler, including cancelling
in-flight calls (see detailed design below). From the client's
perspective, the child process is now free to create new channels and
use gRPC.

1 files changed, 40 insertions, 33 deletions

diff --git a/src/core/lib/gprpp/fork.cc b/src/core/lib/gprpp/fork.cc
index f6d9a87d2c..0288c39680 100644
--- a/src/core/lib/gprpp/fork.cc
+++ b/src/core/lib/gprpp/fork.cc
@@ -157,11 +157,11 @@ class ThreadState {
 }  // namespace
 
 void Fork::GlobalInit() {
-  if (!overrideEnabled_) {
+  if (!override_enabled_) {
 #ifdef GRPC_ENABLE_FORK_SUPPORT
-    supportEnabled_ = true;
+    support_enabled_ = true;
 #else
-    supportEnabled_ = false;
+    support_enabled_ = false;
 #endif
     bool env_var_set = false;
     char* env = gpr_getenv("GRPC_ENABLE_FORK_SUPPORT");
@@ -172,7 +172,7 @@ void Fork::GlobalInit() {
                                      "False", "FALSE", "0"};
       for (size_t i = 0; i < GPR_ARRAY_SIZE(truthy); i++) {
         if (0 == strcmp(env, truthy[i])) {
-          supportEnabled_ = true;
+          support_enabled_ = true;
           env_var_set = true;
           break;
         }
@@ -180,7 +180,7 @@ void Fork::GlobalInit() {
       if (!env_var_set) {
         for (size_t i = 0; i < GPR_ARRAY_SIZE(falsey); i++) {
           if (0 == strcmp(env, falsey[i])) {
-            supportEnabled_ = false;
+            support_enabled_ = false;
             env_var_set = true;
             break;
           }
@@ -189,72 +189,79 @@ void Fork::GlobalInit() {
       gpr_free(env);
     }
   }
-  if (supportEnabled_) {
-    execCtxState_ = grpc_core::New<internal::ExecCtxState>();
-    threadState_ = grpc_core::New<internal::ThreadState>();
+  if (support_enabled_) {
+    exec_ctx_state_ = grpc_core::New<internal::ExecCtxState>();
+    thread_state_ = grpc_core::New<internal::ThreadState>();
   }
 }
 
 void Fork::GlobalShutdown() {
-  if (supportEnabled_) {
-    grpc_core::Delete(execCtxState_);
-    grpc_core::Delete(threadState_);
+  if (support_enabled_) {
+    grpc_core::Delete(exec_ctx_state_);
+    grpc_core::Delete(thread_state_);
   }
 }
 
-bool Fork::Enabled() { return supportEnabled_; }
+bool Fork::Enabled() { return support_enabled_; }
 
 // Testing Only
 void Fork::Enable(bool enable) {
-  overrideEnabled_ = true;
-  supportEnabled_ = enable;
+  override_enabled_ = true;
+  support_enabled_ = enable;
 }
 
 void Fork::IncExecCtxCount() {
-  if (supportEnabled_) {
-    execCtxState_->IncExecCtxCount();
+  if (support_enabled_) {
+    exec_ctx_state_->IncExecCtxCount();
   }
 }
 
 void Fork::DecExecCtxCount() {
-  if (supportEnabled_) {
-    execCtxState_->DecExecCtxCount();
+  if (support_enabled_) {
+    exec_ctx_state_->DecExecCtxCount();
   }
 }
 
+void Fork::SetResetChildPollingEngineFunc(Fork::child_postfork_func func) {
+  reset_child_polling_engine_ = func;
+}
+Fork::child_postfork_func Fork::GetResetChildPollingEngineFunc() {
+  return reset_child_polling_engine_;
+}
+
 bool Fork::BlockExecCtx() {
-  if (supportEnabled_) {
-    return execCtxState_->BlockExecCtx();
+  if (support_enabled_) {
+    return exec_ctx_state_->BlockExecCtx();
   }
   return false;
 }
 
 void Fork::AllowExecCtx() {
-  if (supportEnabled_) {
-    execCtxState_->AllowExecCtx();
+  if (support_enabled_) {
+    exec_ctx_state_->AllowExecCtx();
   }
 }
 
 void Fork::IncThreadCount() {
-  if (supportEnabled_) {
-    threadState_->IncThreadCount();
+  if (support_enabled_) {
+    thread_state_->IncThreadCount();
   }
 }
 
 void Fork::DecThreadCount() {
-  if (supportEnabled_) {
-    threadState_->DecThreadCount();
+  if (support_enabled_) {
+    thread_state_->DecThreadCount();
   }
 }
 void Fork::AwaitThreads() {
-  if (supportEnabled_) {
-    threadState_->AwaitThreads();
+  if (support_enabled_) {
+    thread_state_->AwaitThreads();
   }
 }
 
-internal::ExecCtxState* Fork::execCtxState_ = nullptr;
-internal::ThreadState* Fork::threadState_ = nullptr;
-bool Fork::supportEnabled_ = false;
-bool Fork::overrideEnabled_ = false;
-
+internal::ExecCtxState* Fork::exec_ctx_state_ = nullptr;
+internal::ThreadState* Fork::thread_state_ = nullptr;
+bool Fork::support_enabled_ = false;
+bool Fork::override_enabled_ = false;
+Fork::child_postfork_func Fork::reset_child_polling_engine_ = nullptr;
 }  // namespace grpc_core