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finish basic LB pick logic

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pull/35791/head
Mark D. Roth 1 year ago
parent 474146ab8e
commit 528f64c8bf
2 changed files with 52 additions and 75 deletions
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  1. 105
      src/core/client_channel/client_channel.cc
  2. 22
      src/core/client_channel/client_channel.h

105
src/core/client_channel/client_channel.cc
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@ -1623,74 +1623,34 @@ CallInitiator ClientChannel::CreateLoadBalancedCall(
client_initial_metadata = std::move(client_initial_metadata),
initiator = call.initiator,
handler = std::move(call.handler)]() mutable {
const bool wait_for_ready =
client_initial_metadata->GetOrCreatePointer(WaitForReady())->value;
return Map(
// Wait for the LB picker.
Loop([last_picker =
RefCountedPtr<LoadBalancingPolicy::SubchannelPicker>(),
client_initial_metadata =
std::move(client_initial_metadata)]() mutable {
std::move(client_initial_metadata),
initiator, handler]() mutable {
return Map(
picker_.Next(last_picker),
[last_picker = &last_picker,
client_initial_metadata =
std::move(client_initial_metadata)](
[&last_picker, &client_initial_metadata, &initiator](
RefCountedPtr<LoadBalancingPolicy::SubchannelPicker>
picker) mutable {
// FIXME: if work_serializer_dispatch experiment not enabled, need to
// hop into WorkSerializer to unref previous picker
last_picker = std::move(picker);
// Returns 3 possible things:
// - Continue to queue the pick
// - non-OK status to fail the pick
// - {connected subchannel, LB call tracker}
return PickSubchannel(*last_picker,
client_initial_metadata);
// - a connected subchannel to complete the pick
return PickSubchannel(
*last_picker, client_initial_metadata, initiator);
});
}),
picker_.Next()
resolver_data_for_calls_.NextWhen(
[wait_for_ready](
const absl::StatusOr<ResolverDataForCalls> result) {
// If the resolver reports an error but the call is
// wait_for_ready, keep waiting for the next result
// instead of failing the call.
if (!result.ok()) return !wait_for_ready;
// Not an error. Make sure we actually have a result.
return *result != nullptr;
}),
// Handle resolver result.
[self, initiator = std::move(initiator),
handler = std::move(handler),
client_initial_metadata = std::move(client_initial_metadata)](
ResolverDataForCalls resolver_data) mutable {
// Apply service config to call.
absl::Status status = ApplyServiceConfigToCall(
self.get(), *resolver_data.config_selector,
client_initial_metadata);
if (!status.ok()) return status;
// Now inject initial metadata into the call.
// FIXME: how do I chain this such that it doesn't need another call to
// SpawnGuarded()?
initiator.SpawnGuarded(
"send_initial_metadata",
[initiator, client_initial_metadata =
std::move(client_initial_metadata)]() mutable {
return initiator.PushClientInitialMetadata(
std::move(client_initial_metadata));
});
// Finish constructing the call with the right filter
// stack and destination.
handler.SetStack(std::move(resolver_data.filter_stack));
self->call_destination_->StartCall(std::move(handler));
return absl::OkStatus();
});
// Create call stack on the connected subchannel.
[handler = std::move(handler)](
RefCountedPtr<ConnectedSubchannel> connected_subchannel) {
handler.SetStack(connected_subchannel->GetStack());
connected_subchannel->call_destination_->StartCall(
std::move(handler));
});
});
// Return the initiator.
return call.initiator;
@ -1906,9 +1866,10 @@ void ClientChannel::LoadBalancedCall::RecordLatency() {
}
}
LoopCtl<absl::StatusOr<PickSubchannelResult>> ClientChannel::PickSubchannel(
LoadBalancingPolicy::SubchannelPicker& picker,
ClientMetadataHandle& client_initial_metadata) {
LoopCtl<absl::StatusOr<RefCountedPtr<ConnectedSubchannel>>>
ClientChannel::PickSubchannel(LoadBalancingPolicy::SubchannelPicker& picker,
ClientMetadataHandle& client_initial_metadata,
CallInitiator& call_initiator) {
// Perform LB pick.
LoadBalancingPolicy::PickArgs pick_args;
Slice* path = client_initial_metadata->get_pointer(HttpPathMetadata());
@ -1918,12 +1879,12 @@ LoopCtl<absl::StatusOr<PickSubchannelResult>> ClientChannel::PickSubchannel(
pick_args.call_state = &lb_call_state;
LbMetadata initial_metadata(client_initial_metadata.get());
pick_args.initial_metadata = &initial_metadata;
auto result = picker->Pick(pick_args);
auto result = picker.Pick(pick_args);
// Handle result.
return HandlePickResult<bool>(
&result,
// CompletePick
[this](LoadBalancingPolicy::PickResult::Complete* complete_pick) {
[&](LoadBalancingPolicy::PickResult::Complete* complete_pick) {
if (GRPC_TRACE_FLAG_ENABLED(grpc_client_channel_lb_call_trace)) {
gpr_log(GPR_INFO,
"client_channel=%p lb_call=%p: LB pick succeeded: subchannel=%p",
@ -1934,13 +1895,12 @@ LoopCtl<absl::StatusOr<PickSubchannelResult>> ClientChannel::PickSubchannel(
// holding the data plane mutex.
SubchannelWrapper* subchannel =
static_cast<SubchannelWrapper*>(complete_pick->subchannel.get());
PickSubchannelResult result;
result.connected_subchannel = subchannel->connected_subchannel();
auto connected_subchannel = subchannel->connected_subchannel();
// If the subchannel has no connected subchannel (e.g., if the
// subchannel has moved out of state READY but the LB policy hasn't
// yet seen that change and given us a new picker), then just
// queue the pick. We'll try again as soon as we get a new picker.
if (result.connected_subchannel == nullptr) {
if (connected_subchannel == nullptr) {
if (GRPC_TRACE_FLAG_ENABLED(grpc_client_channel_lb_call_trace)) {
gpr_log(GPR_INFO,
"client_channel=%p lb_call=%p: subchannel returned by LB picker "
@ -1949,10 +1909,25 @@ LoopCtl<absl::StatusOr<PickSubchannelResult>> ClientChannel::PickSubchannel(
}
return Continue{};
}
result.call_tracker =
std::move(complete_pick->subchannel_call_tracker);
if (result.call_tracker_ != nullptr) result.call_tracker_->Start();
return result;
// If the LB policy returned a call tracker, inform it that the
// call is starting and add it to context, so that we can notify
// it when the call finishes.
if (complete_pick->subchannel_call_tracker != nullptr) {
complete_pick->subchannel_call_tracker->Start();
call_initiator.SetContext(
std::move(complete_pick->subchannel_call_tracker));
}
// Now that we're done with client initial metadata, push it
// into the call initiator.
call_initiator.SpawnGuarded(
"send_initial_metadata",
[call_initiator, client_initial_metadata =
std::move(client_initial_metadata)]() mutable {
return call_initiator.PushClientInitialMetadata(
std::move(client_initial_metadata));
});
// Return the connected subchannel.
return connected_subchannel;
},
// QueuePick
[this](LoadBalancingPolicy::PickResult::Queue* /*queue_pick*/) {

22
src/core/client_channel/client_channel.h
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@ -146,16 +146,6 @@ class ClientChannel : public CallFactory {
};
#endif
// The result of the load balancing promise.
struct PickSubchannelResult {
RefCountedPtr<ConnectedSubchannel> connected_subchannel_;
std::unique_ptr<LoadBalancingPolicy::SubchannelCallTrackerInterface>
call_tracker;
};
LoopCtl<absl::StatusOr<PickSubchannelResult>> PickSubchannel(
LoadBalancingPolicy::SubchannelPicker& picker,
ClientMetadataHandle& client_initial_metadata);
void OnResolverResultChangedLocked(Resolver::Result result)
ABSL_EXCLUSIVE_LOCKS_REQUIRED(*work_serializer_);
void OnResolverErrorLocked(absl::Status status)
@ -201,6 +191,18 @@ class ClientChannel : public CallFactory {
const grpc_channel_info* info);
#endif
// Does an LB pick for a call. Returns one of the following things:
// - Continue{}, meaning to queue the pick
// - a non-OK status, meaning to fail the call
// - a connected subchannel, meaning that the pick is complete
// When the pick is complete, pushes client_initial_metadata onto
// call_initiator. Also adds the subchannel call tracker (if any) to
// context.
LoopCtl<absl::StatusOr<RefCountedPtr<ConnectedSubchannel>>> PickSubchannel(
LoadBalancingPolicy::SubchannelPicker& picker,
ClientMetadataHandle& client_initial_metadata,
CallInitiator& call_initiator);
//
// Fields set at construction and never modified.
//

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