2 * Copyright 2016 Facebook, Inc.
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
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7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
12 * http://www.apache.org/licenses/LICENSE-2.0
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
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25 #include <glog/logging.h>
26 #include <folly/RWSpinLock.h>
27 #include <folly/SingletonThreadLocal.h>
31 // Some request context that follows an async request through a process
32 // Everything in the context must be thread safe
36 virtual ~RequestData() = default;
41 // If you do not call create() to create a unique request context,
42 // this default request context will always be returned, and is never
43 // copied between threads.
44 class RequestContext {
46 // Create a unique requext context for this request.
47 // It will be passed between queues / threads (where implemented),
48 // so it should be valid for the lifetime of the request.
49 static void create() {
50 getStaticContext() = std::make_shared<RequestContext>();
53 // Get the current context.
54 static RequestContext* get() {
55 auto context = getStaticContext();
57 static RequestContext defaultContext;
58 return std::addressof(defaultContext);
63 // The following API may be used to set per-request data in a thread-safe way.
64 // This access is still performance sensitive, so please ask if you need help
65 // profiling any use of these functions.
67 const std::string& val, std::unique_ptr<RequestData> data) {
68 folly::RWSpinLock::WriteHolder guard(lock);
69 if (data_.find(val) != data_.end()) {
70 LOG_FIRST_N(WARNING, 1) <<
71 "Called RequestContext::setContextData with data already set";
75 data_[val] = std::move(data);
79 // Unlike setContextData, this method does not panic if the key is already
80 // present. Returns true iff the new value has been inserted.
81 bool setContextDataIfAbsent(const std::string& val,
82 std::unique_ptr<RequestData> data) {
83 folly::RWSpinLock::UpgradedHolder guard(lock);
84 if (data_.find(val) != data_.end()) {
88 folly::RWSpinLock::WriteHolder writeGuard(std::move(guard));
89 data_[val] = std::move(data);
93 bool hasContextData(const std::string& val) {
94 folly::RWSpinLock::ReadHolder guard(lock);
95 return data_.find(val) != data_.end();
98 RequestData* getContextData(const std::string& val) {
99 folly::RWSpinLock::ReadHolder guard(lock);
100 auto r = data_.find(val);
101 if (r == data_.end()) {
104 return r->second.get();
108 void clearContextData(const std::string& val) {
109 folly::RWSpinLock::WriteHolder guard(lock);
113 // The following API is used to pass the context through queues / threads.
114 // saveContext is called to get a shared_ptr to the context, and
115 // setContext is used to reset it on the other side of the queue.
117 // Whenever possible, use RequestContextScopeGuard instead of setContext
118 // to make sure that RequestContext is reset to the original value when
119 // we exit the scope.
121 // A shared_ptr is used, because many request may fan out across
122 // multiple threads, or do post-send processing, etc.
123 static std::shared_ptr<RequestContext>
124 setContext(std::shared_ptr<RequestContext> ctx) {
126 swap(ctx, getStaticContext());
130 static std::shared_ptr<RequestContext> saveContext() {
131 return getStaticContext();
135 static std::shared_ptr<RequestContext>& getStaticContext();
137 folly::RWSpinLock lock;
138 std::map<std::string, std::unique_ptr<RequestData>> data_;
141 class RequestContextScopeGuard {
143 std::shared_ptr<RequestContext> prev_;
146 // Create a new RequestContext and reset to the original value when
147 // this goes out of scope.
148 RequestContextScopeGuard() : prev_(RequestContext::saveContext()) {
149 RequestContext::create();
152 // Set a RequestContext that was previously captured by saveContext(). It will
153 // be automatically reset to the original value when this goes out of scope.
154 explicit RequestContextScopeGuard(std::shared_ptr<RequestContext> ctx)
155 : prev_(RequestContext::setContext(std::move(ctx))) {}
157 ~RequestContextScopeGuard() {
158 RequestContext::setContext(std::move(prev_));