mirror of https://github.com/grpc/grpc.git
Merge pull request #22101 from markdroth/lb_graceful_switcher
Refactor code for gracefully switching child LB policies.pull/22187/head
Mark D. Roth
5 years ago
committed by
GitHub
commit
5e98ad4077
21 changed files with 520 additions and 700 deletions
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//
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// Copyright 2018 gRPC authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#include <grpc/support/port_platform.h> |
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#include "src/core/ext/filters/client_channel/lb_policy/child_policy_handler.h" |
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#include "absl/strings/str_cat.h" |
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#include "src/core/ext/filters/client_channel/lb_policy_registry.h" |
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namespace grpc_core { |
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//
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// ChildPolicyHandler::Helper
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//
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class ChildPolicyHandler::Helper |
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: public LoadBalancingPolicy::ChannelControlHelper { |
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public: |
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explicit Helper(RefCountedPtr<ChildPolicyHandler> parent) |
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: parent_(std::move(parent)) {} |
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~Helper() { parent_.reset(DEBUG_LOCATION, "Helper"); } |
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RefCountedPtr<SubchannelInterface> CreateSubchannel( |
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const grpc_channel_args& args) override { |
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if (parent_->shutting_down_) return nullptr; |
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if (!CalledByCurrentChild() && !CalledByPendingChild()) return nullptr; |
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return parent_->channel_control_helper()->CreateSubchannel(args); |
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} |
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void UpdateState(grpc_connectivity_state state, |
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std::unique_ptr<SubchannelPicker> picker) override { |
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if (parent_->shutting_down_) return; |
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// If this request is from the pending child policy, ignore it until
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// it reports READY, at which point we swap it into place.
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if (CalledByPendingChild()) { |
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if (GRPC_TRACE_FLAG_ENABLED(*(parent_->tracer_))) { |
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gpr_log(GPR_INFO, |
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"[child_policy_handler %p] helper %p: pending child policy %p " |
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"reports state=%s", |
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parent_.get(), this, child_, ConnectivityStateName(state)); |
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} |
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if (state != GRPC_CHANNEL_READY) return; |
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grpc_pollset_set_del_pollset_set( |
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parent_->child_policy_->interested_parties(), |
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parent_->interested_parties()); |
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parent_->child_policy_ = std::move(parent_->pending_child_policy_); |
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} else if (!CalledByCurrentChild()) { |
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// This request is from an outdated child, so ignore it.
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return; |
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} |
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parent_->channel_control_helper()->UpdateState(state, std::move(picker)); |
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} |
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void RequestReresolution() override { |
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if (parent_->shutting_down_) return; |
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// Only forward re-resolution requests from the most recent child,
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// since that's the one that will be receiving any update we receive
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// from the resolver.
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const LoadBalancingPolicy* latest_child_policy = |
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parent_->pending_child_policy_ != nullptr |
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? parent_->pending_child_policy_.get() |
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: parent_->child_policy_.get(); |
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if (child_ != latest_child_policy) return; |
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if (GRPC_TRACE_FLAG_ENABLED(*(parent_->tracer_))) { |
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gpr_log(GPR_INFO, "[child_policy_handler %p] started name re-resolving", |
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parent_.get()); |
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} |
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parent_->channel_control_helper()->RequestReresolution(); |
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} |
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void AddTraceEvent(TraceSeverity severity, StringView message) override { |
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if (parent_->shutting_down_) return; |
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if (!CalledByPendingChild() && !CalledByCurrentChild()) return; |
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parent_->channel_control_helper()->AddTraceEvent(severity, message); |
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} |
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void set_child(LoadBalancingPolicy* child) { child_ = child; } |
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private: |
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bool CalledByPendingChild() const { |
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GPR_ASSERT(child_ != nullptr); |
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return child_ == parent_->pending_child_policy_.get(); |
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} |
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bool CalledByCurrentChild() const { |
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GPR_ASSERT(child_ != nullptr); |
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return child_ == parent_->child_policy_.get(); |
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}; |
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RefCountedPtr<ChildPolicyHandler> parent_; |
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LoadBalancingPolicy* child_ = nullptr; |
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}; |
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//
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// ChildPolicyHandler
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//
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void ChildPolicyHandler::ShutdownLocked() { |
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if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) { |
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gpr_log(GPR_INFO, "[child_policy_handler %p] shutting down", this); |
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} |
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shutting_down_ = true; |
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if (child_policy_ != nullptr) { |
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if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) { |
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gpr_log(GPR_INFO, "[child_policy_handler %p] shutting down lb_policy %p", |
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this, child_policy_.get()); |
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} |
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grpc_pollset_set_del_pollset_set(child_policy_->interested_parties(), |
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interested_parties()); |
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child_policy_.reset(); |
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} |
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if (pending_child_policy_ != nullptr) { |
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if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) { |
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gpr_log(GPR_INFO, |
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"[child_policy_handler %p] shutting down pending lb_policy %p", |
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this, pending_child_policy_.get()); |
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} |
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grpc_pollset_set_del_pollset_set( |
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pending_child_policy_->interested_parties(), interested_parties()); |
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pending_child_policy_.reset(); |
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} |
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} |
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void ChildPolicyHandler::UpdateLocked(UpdateArgs args) { |
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// The name of the policy that this update wants us to use.
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const char* child_policy_name = args.config->name(); |
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// If the child policy name changes, we need to create a new child
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// policy. When this happens, we leave child_policy_ as-is and store
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// the new child policy in pending_child_policy_. Once the new child
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// policy transitions into state READY, we swap it into child_policy_,
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// replacing the original child policy. So pending_child_policy_ is
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// non-null only between when we apply an update that changes the child
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// policy name and when the new child reports state READY.
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//
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// Updates can arrive at any point during this transition. We always
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// apply updates relative to the most recently created child policy,
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// even if the most recent one is still in pending_child_policy_. This
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// is true both when applying the updates to an existing child policy
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// and when determining whether we need to create a new policy.
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//
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// As a result of this, there are several cases to consider here:
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//
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// 1. We have no existing child policy (i.e., this is the first update
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// we receive after being created; in this case, both child_policy_
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// and pending_child_policy_ are null). In this case, we create a
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// new child policy and store it in child_policy_.
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//
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// 2. We have an existing child policy and have no pending child policy
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// from a previous update (i.e., either there has not been a
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// previous update that changed the policy name, or we have already
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// finished swapping in the new policy; in this case, child_policy_
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// is non-null but pending_child_policy_ is null). In this case:
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// a. If child_policy_->name() equals child_policy_name, then we
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// update the existing child policy.
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// b. If child_policy_->name() does not equal child_policy_name,
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// we create a new policy. The policy will be stored in
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// pending_child_policy_ and will later be swapped into
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// child_policy_ by the helper when the new child transitions
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// into state READY.
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//
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// 3. We have an existing child policy and have a pending child policy
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// from a previous update (i.e., a previous update set
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// pending_child_policy_ as per case 2b above and that policy has
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// not yet transitioned into state READY and been swapped into
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// child_policy_; in this case, both child_policy_ and
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// pending_child_policy_ are non-null). In this case:
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// a. If pending_child_policy_->name() equals child_policy_name,
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// then we update the existing pending child policy.
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// b. If pending_child_policy->name() does not equal
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// child_policy_name, then we create a new policy. The new
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// policy is stored in pending_child_policy_ (replacing the one
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// that was there before, which will be immediately shut down)
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// and will later be swapped into child_policy_ by the helper
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// when the new child transitions into state READY.
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const bool create_policy = |
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// case 1
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child_policy_ == nullptr || |
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// case 2b
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(pending_child_policy_ == nullptr && |
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strcmp(child_policy_->name(), child_policy_name) != 0) || |
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// case 3b
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(pending_child_policy_ != nullptr && |
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strcmp(pending_child_policy_->name(), child_policy_name) != 0); |
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LoadBalancingPolicy* policy_to_update = nullptr; |
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if (create_policy) { |
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// Cases 1, 2b, and 3b: create a new child policy.
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// If child_policy_ is null, we set it (case 1), else we set
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// pending_child_policy_ (cases 2b and 3b).
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if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) { |
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gpr_log(GPR_INFO, |
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"[child_policy_handler %p] creating new %schild policy %s", this, |
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child_policy_ == nullptr ? "" : "pending ", child_policy_name); |
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} |
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auto& lb_policy = |
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child_policy_ == nullptr ? child_policy_ : pending_child_policy_; |
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lb_policy = CreateChildPolicy(child_policy_name, *args.args); |
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policy_to_update = lb_policy.get(); |
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} else { |
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// Cases 2a and 3a: update an existing policy.
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// If we have a pending child policy, send the update to the pending
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// policy (case 3a), else send it to the current policy (case 2a).
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policy_to_update = pending_child_policy_ != nullptr |
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? pending_child_policy_.get() |
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: child_policy_.get(); |
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} |
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GPR_ASSERT(policy_to_update != nullptr); |
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// Update the policy.
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if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) { |
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gpr_log(GPR_INFO, "[child_policy_handler %p] updating %schild policy %p", |
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this, |
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policy_to_update == pending_child_policy_.get() ? "pending " : "", |
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policy_to_update); |
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} |
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policy_to_update->UpdateLocked(std::move(args)); |
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} |
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void ChildPolicyHandler::ExitIdleLocked() { |
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if (child_policy_ != nullptr) { |
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child_policy_->ExitIdleLocked(); |
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if (pending_child_policy_ != nullptr) { |
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pending_child_policy_->ExitIdleLocked(); |
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} |
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} |
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} |
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void ChildPolicyHandler::ResetBackoffLocked() { |
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if (child_policy_ != nullptr) { |
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child_policy_->ResetBackoffLocked(); |
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if (pending_child_policy_ != nullptr) { |
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pending_child_policy_->ResetBackoffLocked(); |
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} |
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} |
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} |
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OrphanablePtr<LoadBalancingPolicy> ChildPolicyHandler::CreateChildPolicy( |
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const char* child_policy_name, const grpc_channel_args& args) { |
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Helper* helper = new Helper(Ref(DEBUG_LOCATION, "Helper")); |
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LoadBalancingPolicy::Args lb_policy_args; |
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lb_policy_args.combiner = combiner(); |
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lb_policy_args.channel_control_helper = |
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std::unique_ptr<ChannelControlHelper>(helper); |
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lb_policy_args.args = &args; |
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OrphanablePtr<LoadBalancingPolicy> lb_policy = |
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LoadBalancingPolicyRegistry::CreateLoadBalancingPolicy( |
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child_policy_name, std::move(lb_policy_args)); |
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if (GPR_UNLIKELY(lb_policy == nullptr)) { |
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gpr_log(GPR_ERROR, "could not create LB policy \"%s\"", child_policy_name); |
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return nullptr; |
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} |
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helper->set_child(lb_policy.get()); |
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if (GRPC_TRACE_FLAG_ENABLED(*tracer_)) { |
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gpr_log(GPR_INFO, |
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"[child_policy_handler %p] created new LB policy \"%s\" (%p)", this, |
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child_policy_name, lb_policy.get()); |
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} |
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channel_control_helper()->AddTraceEvent( |
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ChannelControlHelper::TRACE_INFO, |
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absl::StrCat("Created new LB policy \"", child_policy_name, "\"")); |
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grpc_pollset_set_add_pollset_set(lb_policy->interested_parties(), |
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interested_parties()); |
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return lb_policy; |
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} |
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} // namespace grpc_core
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@ -0,0 +1,66 @@ |
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//
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// Copyright 2018 gRPC authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_CHILD_POLICY_HANDLER_H |
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#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_CHILD_POLICY_HANDLER_H |
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#include <grpc/support/port_platform.h> |
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#include "src/core/ext/filters/client_channel/lb_policy.h" |
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#include "src/core/lib/debug/trace.h" |
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#include "src/core/lib/gprpp/orphanable.h" |
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namespace grpc_core { |
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// A class that makes it easy to gracefully switch child policies.
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//
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// Callers should instantiate this instead of using
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// LoadBalancingPolicyRegistry::CreateLoadBalancingPolicy(). Once
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// instantiated, this object will automatically take care of
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// constructing the child policy as needed upon receiving an update.
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class ChildPolicyHandler : public LoadBalancingPolicy { |
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public: |
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ChildPolicyHandler(Args args, TraceFlag* tracer) |
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: LoadBalancingPolicy(std::move(args)), tracer_(tracer) {} |
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virtual const char* name() const override { return "child_policy_handler"; } |
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void UpdateLocked(UpdateArgs args) override; |
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void ExitIdleLocked() override; |
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void ResetBackoffLocked() override; |
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private: |
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class Helper; |
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void ShutdownLocked() override; |
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OrphanablePtr<LoadBalancingPolicy> CreateChildPolicy( |
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const char* child_policy_name, const grpc_channel_args& args); |
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// Passed in from caller at construction time.
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TraceFlag* tracer_; |
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bool shutting_down_ = false; |
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// Child LB policy.
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OrphanablePtr<LoadBalancingPolicy> child_policy_; |
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OrphanablePtr<LoadBalancingPolicy> pending_child_policy_; |
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}; |
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} // namespace grpc_core
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#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_CHILD_POLICY_HANDLER_H \ |
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*/ |
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