1 /*
2 * Copyright (c) 2017, The Linux Foundation. All rights reserved.
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28 */
29 
30 #ifndef __SYNC_TASK_H__
31 #define __SYNC_TASK_H__
32 
33 #include <thread>
34 #include <mutex>
35 #include <condition_variable>   // NOLINT
36 
37 namespace sdm {
38 
39 template <class TaskCode>
40 class SyncTask {
41  public:
42   // This class need to be overridden by caller to pass on a task context.
43   class TaskContext {
44    public:
~TaskContext()45     virtual ~TaskContext() { }
46   };
47 
48   // Methods to callback into caller for command codes executions in worker thread.
49   class TaskHandler {
50    public:
~TaskHandler()51     virtual ~TaskHandler() { }
52     virtual void OnTask(const TaskCode &task_code, TaskContext *task_context) = 0;
53   };
54 
SyncTask(TaskHandler & task_handler)55   explicit SyncTask(TaskHandler &task_handler) : task_handler_(task_handler) {
56     // Block caller thread until worker thread has started and ready to listen to task commands.
57     // Worker thread will signal as soon as callback is received in the new thread.
58     std::unique_lock<std::mutex> caller_lock(caller_mutex_);
59     std::thread worker_thread(SyncTaskThread, this);
60     worker_thread_.swap(worker_thread);
61     caller_cv_.wait(caller_lock);
62   }
63 
~SyncTask()64   ~SyncTask() {
65     // Task code does not matter here.
66     PerformTask(task_code_, nullptr, true);
67     worker_thread_.join();
68   }
69 
PerformTask(const TaskCode & task_code,TaskContext * task_context)70   void PerformTask(const TaskCode &task_code, TaskContext *task_context) {
71     PerformTask(task_code, task_context, false);
72   }
73 
74  private:
PerformTask(const TaskCode & task_code,TaskContext * task_context,bool terminate)75   void PerformTask(const TaskCode &task_code, TaskContext *task_context, bool terminate) {
76     std::unique_lock<std::mutex> caller_lock(caller_mutex_);
77 
78     // New scope to limit scope of worker lock to this block.
79     {
80       // Set task command code and notify worker thread.
81       std::unique_lock<std::mutex> worker_lock(worker_mutex_);
82       task_code_ = task_code;
83       task_context_ = task_context;
84       worker_thread_exit_ = terminate;
85       pending_code_ = true;
86       worker_cv_.notify_one();
87     }
88 
89     // Wait for worker thread to finish and signal.
90     caller_cv_.wait(caller_lock);
91   }
92 
SyncTaskThread(SyncTask * sync_task)93   static void SyncTaskThread(SyncTask *sync_task) {
94     if (sync_task) {
95       sync_task->OnThreadCallback();
96     }
97   }
98 
OnThreadCallback()99   void OnThreadCallback() {
100     // Acquire worker lock and start waiting for events.
101     // Wait must start before caller thread can post events, otherwise posted events will be lost.
102     // Caller thread will be blocked until worker thread signals readiness.
103     std::unique_lock<std::mutex> worker_lock(worker_mutex_);
104 
105     // New scope to limit scope of caller lock to this block.
106     {
107       // Signal caller thread that worker thread is ready to listen to events.
108       std::unique_lock<std::mutex> caller_lock(caller_mutex_);
109       caller_cv_.notify_one();
110     }
111 
112     while (!worker_thread_exit_) {
113       // Add predicate to handle spurious interrupts.
114       // Wait for caller thread to signal new command codes.
115       worker_cv_.wait(worker_lock, [this] { return pending_code_; });
116 
117       // Call task handler which is implemented by the caller.
118       if (!worker_thread_exit_) {
119         task_handler_.OnTask(task_code_, task_context_);
120       }
121 
122       pending_code_ = false;
123       // Notify completion of current task to the caller thread which is blocked.
124       std::unique_lock<std::mutex> caller_lock(caller_mutex_);
125       caller_cv_.notify_one();
126     }
127   }
128 
129   TaskHandler &task_handler_;
130   TaskCode task_code_;
131   TaskContext *task_context_ = nullptr;
132   std::thread worker_thread_;
133   std::mutex caller_mutex_;
134   std::mutex worker_mutex_;
135   std::condition_variable caller_cv_;
136   std::condition_variable worker_cv_;
137   bool worker_thread_exit_ = false;
138   bool pending_code_ = false;
139 };
140 
141 }  // namespace sdm
142 
143 #endif  // __SYNC_TASK_H__
144