/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements. See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership. The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License. You may obtain a copy of the License at
+ * Copyright 2004-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied. See the License for the
- * specific language governing permissions and limitations
- * under the License.
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
*/
+
#pragma once
#include <map>
#include <memory>
-#include <glog/logging.h>
-#include <folly/ThreadLocal.h>
-#include <folly/RWSpinLock.h>
-
-/**
- * In many cases this header is included as a
- * dependency to libraries which do not need
- * command line flags. GFLAGS is a large binary
- * and thus we do this so that a library which
- * is size sensitive doesn't have to pull in
- * GFLAGS if it doesn't want to.
- */
-#ifndef NO_LIB_GFLAGS
- #include <gflags/gflags.h>
- DECLARE_bool(enable_request_context);
-#endif
-namespace folly {
+#include <folly/SharedMutex.h>
+#include <folly/Synchronized.h>
-#ifdef NO_LIB_GFLAGS
- extern bool FLAGS_enable_request_context;
-#endif
+namespace folly {
// Some request context that follows an async request through a process
// Everything in the context must be thread safe
class RequestData {
public:
- virtual ~RequestData() {}
+ virtual ~RequestData() = default;
+ // Avoid calling RequestContext::setContextData, setContextDataIfAbsent, or
+ // clearContextData from these callbacks. Doing so will cause deadlock. We
+ // could fix these deadlocks, but only at significant performance penalty, so
+ // just don't do it!
+ virtual void onSet() {}
+ virtual void onUnset() {}
};
class RequestContext;
// If you do not call create() to create a unique request context,
// this default request context will always be returned, and is never
// copied between threads.
-extern RequestContext* defaultContext;
-
class RequestContext {
public:
- // Create a unique requext context for this request.
+ // Create a unique request context for this request.
// It will be passed between queues / threads (where implemented),
// so it should be valid for the lifetime of the request.
- static bool create() {
- if(!FLAGS_enable_request_context) {
- return false;
- }
- bool prev = getStaticContext().get() != nullptr;
- getStaticContext().reset(new std::shared_ptr<RequestContext>(
- std::make_shared<RequestContext>()));
- return prev;
+ static void create() {
+ setContext(std::make_shared<RequestContext>());
}
// Get the current context.
- static RequestContext* get() {
- if (!FLAGS_enable_request_context ||
- getStaticContext().get() == nullptr) {
- if (defaultContext == nullptr) {
- defaultContext = new RequestContext;
- }
- return defaultContext;
- }
- return getStaticContext().get()->get();
- }
+ static RequestContext* get();
// The following API may be used to set per-request data in a thread-safe way.
// This access is still performance sensitive, so please ask if you need help
// profiling any use of these functions.
void setContextData(
- const std::string& val, std::unique_ptr<RequestData> data) {
- if (!FLAGS_enable_request_context) {
- return;
- }
-
- folly::RWSpinLock::WriteHolder guard(lock);
- if (data_.find(val) != data_.end()) {
- LOG_FIRST_N(WARNING, 1) <<
- "Called RequestContext::setContextData with data already set";
-
- data_[val] = nullptr;
- } else {
- data_[val] = std::move(data);
- }
- }
+ const std::string& val,
+ std::unique_ptr<RequestData> data);
- bool hasContextData(const std::string& val) {
- folly::RWSpinLock::ReadHolder guard(lock);
- return data_.find(val) != data_.end();
- }
+ // Unlike setContextData, this method does not panic if the key is already
+ // present. Returns true iff the new value has been inserted.
+ bool setContextDataIfAbsent(
+ const std::string& val,
+ std::unique_ptr<RequestData> data);
- RequestData* getContextData(const std::string& val) {
- folly::RWSpinLock::ReadHolder guard(lock);
- auto r = data_.find(val);
- if (r == data_.end()) {
- return nullptr;
- } else {
- return r->second.get();
- }
- }
+ bool hasContextData(const std::string& val) const;
- void clearContextData(const std::string& val) {
- folly::RWSpinLock::WriteHolder guard(lock);
- data_.erase(val);
- }
+ RequestData* getContextData(const std::string& val);
+ const RequestData* getContextData(const std::string& val) const;
+
+ void onSet();
+ void onUnset();
+
+ void clearContextData(const std::string& val);
// The following API is used to pass the context through queues / threads.
- // saveContext is called to geta shared_ptr to the context, and
+ // saveContext is called to get a shared_ptr to the context, and
// setContext is used to reset it on the other side of the queue.
//
+ // Whenever possible, use RequestContextScopeGuard instead of setContext
+ // to make sure that RequestContext is reset to the original value when
+ // we exit the scope.
+ //
// A shared_ptr is used, because many request may fan out across
// multiple threads, or do post-send processing, etc.
-
- static std::shared_ptr<RequestContext>
- setContext(std::shared_ptr<RequestContext> ctx) {
- if (FLAGS_enable_request_context) {
- std::shared_ptr<RequestContext> old_ctx;
- if (getStaticContext().get()) {
- old_ctx = *getStaticContext().get();
- }
- if (ctx == nullptr) {
- getStaticContext().reset(nullptr);
- } else {
- getStaticContext().reset(new std::shared_ptr<RequestContext>(ctx));
- }
- return old_ctx;
- }
- return std::shared_ptr<RequestContext>();
- }
+ static std::shared_ptr<RequestContext> setContext(
+ std::shared_ptr<RequestContext> ctx);
static std::shared_ptr<RequestContext> saveContext() {
- if (!FLAGS_enable_request_context) {
- return std::shared_ptr<RequestContext>();
- }
- if (getStaticContext().get() == nullptr) {
- return std::shared_ptr<RequestContext>();
- } else {
- return *getStaticContext().get();
- }
- }
-
- // Used to solve static destruction ordering issue. Any static object
- // that uses RequestContext must call this function in its constructor.
- //
- // See below link for more details.
- // http://stackoverflow.com/questions/335369/
- // finding-c-static-initialization-order-problems#335746
- static folly::ThreadLocalPtr<std::shared_ptr<RequestContext>>&
- getStaticContext() {
- static folly::ThreadLocalPtr<std::shared_ptr<RequestContext> > context;
- return context;
+ return getStaticContext();
}
private:
- folly::RWSpinLock lock;
- std::map<std::string, std::unique_ptr<RequestData>> data_;
+ static std::shared_ptr<RequestContext>& getStaticContext();
+
+ using Data = std::map<std::string, std::unique_ptr<RequestData>>;
+ folly::Synchronized<Data, folly::SharedMutex> data_;
};
-/**
- * Set the request context for a specific scope. For example,
- * if you ran a part of a request in another thread you could
- * use RequestContextGuard to copy apply the request context
- * inside the other therad.
- */
-class RequestContextGuard {
+class RequestContextScopeGuard {
+ private:
+ std::shared_ptr<RequestContext> prev_;
+
public:
- explicit RequestContextGuard(std::shared_ptr<RequestContext> ctx) {
- oldctx_ = RequestContext::setContext(std::move(ctx));
+ RequestContextScopeGuard(const RequestContextScopeGuard&) = delete;
+ RequestContextScopeGuard& operator=(const RequestContextScopeGuard&) = delete;
+ RequestContextScopeGuard(RequestContextScopeGuard&&) = delete;
+ RequestContextScopeGuard& operator=(RequestContextScopeGuard&&) = delete;
+
+ // Create a new RequestContext and reset to the original value when
+ // this goes out of scope.
+ RequestContextScopeGuard() : prev_(RequestContext::saveContext()) {
+ RequestContext::create();
}
- ~RequestContextGuard() {
- RequestContext::setContext(std::move(oldctx_));
+ // Set a RequestContext that was previously captured by saveContext(). It will
+ // be automatically reset to the original value when this goes out of scope.
+ explicit RequestContextScopeGuard(std::shared_ptr<RequestContext> ctx)
+ : prev_(RequestContext::setContext(std::move(ctx))) {
}
- private:
- std::shared_ptr<RequestContext> oldctx_;
+ ~RequestContextScopeGuard() {
+ RequestContext::setContext(std::move(prev_));
+ }
};
-
}
projects / folly.git / blobdiff