当向Executor(例如tf::Executor::run)提交任务流时,Executor返回一个tf::Future对象,该对象将保存执行结果。tf::Future是来自std::future的派生类。除了std::future的基本方法外,您还可以调用tf::Future::cancel来取消正在运行的任务流的执行。以下示例取消了任务流的提交,该任务流包含1000个任务,每个任务运行一秒钟。
cpp
#include <taskflow/taskflow.hpp>
int main() {
tf::Executor executor;
tf::Taskflow taskflow;
for(int i=0; i<1000; i++) {
taskflow.emplace([](){
std::this_thread::sleep_for(std::chrono::seconds(1));
std::cout<<"Task\n";
});
}
// submit the taskflow
tf::Future<void> fu = executor.run(taskflow);
// std::this_thread::sleep_for(std::chrono::seconds(2));
// request to cancel the above submitted execution
fu.cancel();
// wait until the cancellation completes
fu.get();
taskflow.dump(std::cout);
}
当请求取消时,executor将停止调度任务流的其余Task。但已经运行的Task将继续完成。当所有这些运行Task完成后,取消被视为完成。要等待取消完成,您可以明确调用tf::Future::get, 注意, 一定要调用tf::Future::get等待executor执行完毕,否则可能会有未知的风险:
cpp
tf::Executor executor;
{
tf::Taskflow taskflow;
for(int i=0; i<1000; i++) {
taskflow.emplace([](){});
}
tf::Future fu = executor.run(taskflow);
fu.cancel(); // there can still be task running after cancellation
} // destroying taskflow here can result in undefined behavior
tf::Future::cancel不保证立即取消。
性能分析
所有任务流程序都带有一个轻量级分析模块,以观察每个executor中的Worker活动。要启用分析器,需要将环境变量TF_ENABLE_PROFILER设置为存储分析结果的文件名。
cpp
~$ TF_ENABLE_PROFILER=result.json ./my_taskflow
~$ cat result.json
[
{"executor":"0","data":[{"worker":12,"level":0,"data":[{"span":[72,117],"name":"12_0","type":"static"},{"span":[121,123],"name":"12_1","type":"static"},{"span":[123,125],"name":"12_2","type":"static"},{"span":[125,127],"name":"12_3","type":"static"}]}]}
]
然后将下面的json文本拷贝到:Taskflow Profiler, 进行可视化分析。