3 * Copyright 2016 gRPC authors.
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
9 * http://www.apache.org/licenses/LICENSE-2.0
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12 * distributed under the License is distributed on an "AS IS" BASIS,
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14 * See the License for the specific language governing permissions and
15 * limitations under the License.
19 #ifndef GRPC_INTERNAL_CPP_THREAD_MANAGER_H
20 #define GRPC_INTERNAL_CPP_THREAD_MANAGER_H
22 #include <condition_variable>
27 #include <grpcpp/support/config.h>
29 #include "src/core/lib/gprpp/sync.h"
30 #include "src/core/lib/gprpp/thd.h"
31 #include "src/core/lib/iomgr/resource_quota.h"
37 explicit ThreadManager(const char* name, grpc_resource_quota* resource_quota,
38 int min_pollers, int max_pollers);
39 virtual ~ThreadManager();
41 // Initializes and Starts the Rpc Manager threads
44 // The return type of PollForWork() function
45 enum WorkStatus { WORK_FOUND, SHUTDOWN, TIMEOUT };
47 // "Polls" for new work.
48 // If the return value is WORK_FOUND:
49 // - The implementaion of PollForWork() MAY set some opaque identifier to
50 // (identify the work item found) via the '*tag' parameter
51 // - The implementaion MUST set the value of 'ok' to 'true' or 'false'. A
52 // value of 'false' indicates some implemenation specific error (that is
53 // neither SHUTDOWN nor TIMEOUT)
54 // - ThreadManager does not interpret the values of 'tag' and 'ok'
55 // - ThreadManager WILL call DoWork() and pass '*tag' and 'ok' as input to
58 // If the return value is SHUTDOWN:,
59 // - ThreadManager WILL NOT call DoWork() and terminates the thread
61 // If the return value is TIMEOUT:,
62 // - ThreadManager WILL NOT call DoWork()
63 // - ThreadManager MAY terminate the thread depending on the current number
64 // of active poller threads and mix_pollers/max_pollers settings
65 // - Also, the value of timeout is specific to the derived class
67 virtual WorkStatus PollForWork(void** tag, bool* ok) = 0;
69 // The implementation of DoWork() is supposed to perform the work found by
70 // PollForWork(). The tag and ok parameters are the same as returned by
71 // PollForWork(). The resources parameter indicates that the call actually
72 // has the resources available for performing the RPC's work. If it doesn't,
73 // the implementation should fail it appropriately.
75 // The implementation of DoWork() should also do any setup needed to ensure
76 // that the next call to PollForWork() (not necessarily by the current thread)
77 // actually finds some work
78 virtual void DoWork(void* tag, bool ok, bool resources) = 0;
80 // Mark the ThreadManager as shutdown and begin draining the work. This is a
81 // non-blocking call and the caller should call Wait(), a blocking call which
82 // returns only once the shutdown is complete
83 virtual void Shutdown();
85 // Has Shutdown() been called
88 // A blocking call that returns only after the ThreadManager has shutdown and
89 // all the threads have drained all the outstanding work
92 // Max number of concurrent threads that were ever active in this thread
93 // manager so far. This is useful for debugging purposes (and in unit tests)
94 // to check if resource_quota is properly being enforced.
95 int GetMaxActiveThreadsSoFar();
98 // Helper wrapper class around grpc_core::Thread. Takes a ThreadManager object
99 // and starts a new grpc_core::Thread to calls the Run() function.
101 // The Run() function calls ThreadManager::MainWorkLoop() function and once
102 // that completes, it marks the WorkerThread completed by calling
103 // ThreadManager::MarkAsCompleted()
105 // WHY IS THIS NEEDED?:
106 // When a thread terminates, some other thread *must* call Join() on that
107 // thread so that the resources are released. Having a WorkerThread wrapper
108 // will make this easier. Once Run() completes, each thread calls the
109 // following two functions:
110 // ThreadManager::CleanupCompletedThreads()
111 // ThreadManager::MarkAsCompleted()
113 // - MarkAsCompleted() puts the WorkerThread object in the ThreadManger's
114 // completed_threads_ list
115 // - CleanupCompletedThreads() calls "Join()" on the threads that are already
116 // in the completed_threads_ list (since a thread cannot call Join() on
117 // itself, it calls CleanupCompletedThreads() *before* calling
118 // MarkAsCompleted())
120 // TODO(sreek): Consider creating the threads 'detached' so that Join() need
121 // not be called (and the need for this WorkerThread class is eliminated)
124 WorkerThread(ThreadManager* thd_mgr);
128 // Calls thd_mgr_->MainWorkLoop() and once that completes, calls
129 // thd_mgr_>MarkAsCompleted(this) to mark the thread as completed
132 ThreadManager* const thd_mgr_;
133 grpc_core::Thread thd_;
136 // The main function in ThreadManager
139 void MarkAsCompleted(WorkerThread* thd);
140 void CleanupCompletedThreads();
142 // Protects shutdown_, num_pollers_, num_threads_ and
143 // max_active_threads_sofar_
144 grpc_core::Mutex mu_;
147 grpc_core::CondVar shutdown_cv_;
149 // The resource user object to use when requesting quota to create threads
151 // Note: The user of this ThreadManager object must create grpc_resource_quota
152 // object (that contains the actual max thread quota) and a grpc_resource_user
153 // object through which quota is requested whenver new threads need to be
155 grpc_resource_user* resource_user_;
157 // Number of threads doing polling
160 // The minimum and maximum number of threads that should be doing polling
164 // The total number of threads currently active (includes threads includes the
165 // threads that are currently polling i.e num_pollers_)
168 // See GetMaxActiveThreadsSoFar()'s description.
169 // To be more specific, this variable tracks the max value num_threads_ was
171 int max_active_threads_sofar_;
173 grpc_core::Mutex list_mu_;
174 std::list<WorkerThread*> completed_threads_;
179 #endif // GRPC_INTERNAL_CPP_THREAD_MANAGER_H