2 * Copyright 2016 Facebook, Inc.
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25 #include <folly/RWSpinLock.h>
29 // Some request context that follows an async request through a process
30 // Everything in the context must be thread safe
34 virtual ~RequestData() = default;
35 virtual void onSet() {}
36 virtual void onUnset() {}
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 request 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 setContext(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,
68 std::unique_ptr<RequestData> data);
70 // Unlike setContextData, this method does not panic if the key is already
71 // present. Returns true iff the new value has been inserted.
72 bool setContextDataIfAbsent(
73 const std::string& val,
74 std::unique_ptr<RequestData> data);
76 bool hasContextData(const std::string& val) const;
78 RequestData* getContextData(const std::string& val);
79 const RequestData* getContextData(const std::string& val) const;
84 void clearContextData(const std::string& val);
86 // The following API is used to pass the context through queues / threads.
87 // saveContext is called to get a shared_ptr to the context, and
88 // setContext is used to reset it on the other side of the queue.
90 // Whenever possible, use RequestContextScopeGuard instead of setContext
91 // to make sure that RequestContext is reset to the original value when
94 // A shared_ptr is used, because many request may fan out across
95 // multiple threads, or do post-send processing, etc.
96 static std::shared_ptr<RequestContext> setContext(
97 std::shared_ptr<RequestContext> ctx);
99 static std::shared_ptr<RequestContext> saveContext() {
100 return getStaticContext();
104 static std::shared_ptr<RequestContext>& getStaticContext();
106 mutable folly::RWSpinLock lock;
107 std::map<std::string, std::unique_ptr<RequestData>> data_;
110 class RequestContextScopeGuard {
112 std::shared_ptr<RequestContext> prev_;
115 // Create a new RequestContext and reset to the original value when
116 // this goes out of scope.
117 RequestContextScopeGuard() : prev_(RequestContext::saveContext()) {
118 RequestContext::create();
121 // Set a RequestContext that was previously captured by saveContext(). It will
122 // be automatically reset to the original value when this goes out of scope.
123 explicit RequestContextScopeGuard(std::shared_ptr<RequestContext> ctx)
124 : prev_(RequestContext::setContext(std::move(ctx))) {}
126 ~RequestContextScopeGuard() {
127 RequestContext::setContext(std::move(prev_));