Question-4: Can we reuse that same thread object for different tasks after join()?
Yes we can use same thread object to call 3 different task one after other as given in following example.
For better understanding please copy and paste given code and try to run by yourself.
| #include<iostream> #include<thread> //Thread Header #include<chrono> using namespace std; //actual task to be performed //by our thread void displayActivity() { cout<<"www.techsujhav.com : "<<endl; std::this_thread::sleep_for(60s); } void displayTask() { cout<<"www.techsujhav.com : New Task"<<endl; std::this_thread::sleep_for(60s); } int main() { cout<<"Going to start thread"<<endl; {//New scope started. std::thread t_obj(displayActivity); cout<<"Thread Id ="<<t_obj.get_id()<<endl; cout<<"Before Join, (ACTIVE) joinable=" <<t_obj.joinable()<<endl; t_obj.join(); cout<<"After Join, (ACTIVE) joinable=" <<t_obj.joinable()<<endl<<endl; cout<<"REUSING Thread Object"<<endl; t_obj=std::thread(displayActivity); cout<<"*** Thread Id ="<<t_obj.get_id()<<endl; cout<<"*** Before Join, (ACTIVE) joinable=" <<t_obj.joinable()<<endl; t_obj.join(); cout<<"***After Join, (ACTIVE) joinable=" <<t_obj.joinable()<<endl<<endl; cout<<"REUSING Thread Object with NEW Task"<<endl; t_obj=std::thread(displayTask); cout<<"### Thread Id ="<<t_obj.get_id()<<endl; cout<<"### Before Join, (ACTIVE) joinable=" <<t_obj.joinable()<<endl; t_obj.join(); cout<<"### After Join, (ACTIVE) joinable=" <<t_obj.joinable()<<endl<<endl; cout<<"Going out of scope"<<endl; } cout<<"Main Exit"<<endl; return 0; } |
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TechSujhav@TEAM:~/thread$ ./join Going to start thread Thread Id
=140527220852480 Before Join, (ACTIVE) joinable=1 www.techsujhav.com : After Join, (ACTIVE) joinable=0
REUSING Thread Object *** Thread Id
=140527220852480 *** Before Join, (ACTIVE) joinable=1 www.techsujhav.com : ***After Join, (ACTIVE) joinable=0
REUSING Thread Object with NEW Task ### Thread Id =140527220852480 ### Before Join, (ACTIVE) joinable=1 www.techsujhav.com : New Task ### After Join, (ACTIVE) joinable=0
Going out of scope Main Exit |
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Explanation: Important thing to note here is thread Id is same in all 3 calls. Because we are using the same thread-object in every call However, it does not imply that same thread is used by operating
system, every time a new thread is generated. We can check this on any Linux
system. If you running following commands from other terminal, you would come to know. Please check below output. |
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TechSujhav@TEAM:~$ ps –ef |grep –i join <to get process id of ./join> TechSujhav@TEAM:~$ top -H -p 43835 < process id of ./join >
top - 21:48:21 up 187
days, 21:21, 4 users, load average: 0.00, 0.00, 0.00 Threads: 2 total, 0 running, 2 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.0 us, 0.0 sy,
0.0 ni,100.0 id, 0.0 wa, 0.0 hi,
0.0 si, 0.0 st KiB Mem : 19772300+total, 59427144 free, 1011180 used, 13728468+buff/cache KiB Swap: 8388604 total, 8347236 free, 41368 used. 19526404+avail Mem
PID USER PR
NI VIRT RES
SHR S %CPU %MEM TIME+
COMMAND 43835 TechSujhav 20 0
24376 1888 1736 S
0.0 0.0 0:00.00 join 43836 TechSujhav 20 0
24376 1888 1736 S
0.0 0.0 0:00.00 join
top - 21:48:45 up 187
days, 21:22, 4 users, load average: 0.00, 0.00, 0.00 Threads: 2 total, 0 running, 2 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.0 us, 0.0 sy,
0.0 ni,100.0 id, 0.0 wa, 0.0 hi,
0.0 si, 0.0 st KiB Mem : 19772300+total, 59427972 free, 1010344 used, 13728468+buff/cache KiB Swap: 8388604 total, 8347236 free, 41368 used. 19526488+avail Mem
PID USER PR
NI VIRT RES
SHR S %CPU %MEM TIME+
COMMAND 43835 TechSujhav 20 0
89912 1956 1800 S
0.0 0.0 0:00.00 join 44291 TechSujhav 20 0
89912 1956 1800 S
0.0 0.0 0:00.00 join
top - 21:49:51 up 187
days, 21:23, 4 users, load average: 0.00, 0.00, 0.00 Threads: 2 total, 0 running, 2 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.0 us, 0.0 sy,
0.0 ni,100.0 id, 0.0 wa, 0.0 hi,
0.0 si, 0.0 st KiB Mem : 19772300+total, 59428580 free, 1009708 used, 13728472+buff/cache KiB Swap: 8388604 total, 8347236 free, 41368 used. 19526552+avail Mem
PID USER PR
NI VIRT RES
SHR S %CPU %MEM TIME+
COMMAND 43835 TechSujhav 20 0
89912 1956 1800 S
0.0 0.0 0:00.00 join 44651 TechSujhav 20 0
89912 1956 1800 S
0.0 0.0 0:00.00 join
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Question -3: What will happen if we call join again on same thread?
PREV:: What will happen if we call join again on same thread.
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