WEBVTT 00:06.570 --> 00:08.220 So welcome back, guys. 00:08.250 --> 00:13.850 Now, in this section of the course, we will going to understand what are joinable and detached threads, 00:13.860 --> 00:17.130 what are their properties and how do they work. 00:18.360 --> 00:25.740 So to start with a thread when created using p thread underscore create API, it can be created in one 00:25.740 --> 00:31.710 of the two modes that is, either the thread could be joinable or the thread is detached. 00:31.710 --> 00:32.400 Right. 00:32.430 --> 00:39.210 We pass an argument to this p thread underscore create API which decides whether the new thread that 00:39.210 --> 00:42.900 will going to be created is a joinable thread or detached thread. 00:42.930 --> 00:46.980 We will see in the demo program how to specify that argument. 00:47.010 --> 00:51.750 Now let us first try to understand what are joinable threads, what are their properties? 00:51.750 --> 00:54.570 What are their benefits and how do they work? 00:56.300 --> 01:01.730 So let us suppose that you have written a multithreaded program, and in that multithreaded program 01:01.730 --> 01:03.500 you have one of the threads. 01:03.530 --> 01:06.420 Let us call that thread as parent thread. 01:06.440 --> 01:07.160 Right. 01:07.910 --> 01:14.900 Now, when this parent thread was executing in its execution flow, let us say that at some point of 01:14.900 --> 01:19.790 time the parent thread decides to create another thread, right? 01:19.820 --> 01:26.660 So at point F, which is a fork point, the parent thread invokes an API thread, underscore, create 01:26.660 --> 01:29.690 and create a new thread in joinable mode. 01:29.750 --> 01:30.500 Right. 01:30.530 --> 01:34.640 So let us suppose that this particular thread is a joinable thread. 01:35.180 --> 01:43.040 So after the fork point f the parent thread continue along the course of its execution flow and new 01:43.040 --> 01:50.270 joinable thread that is created will also start doing its work and continue to execute in its own execution 01:50.270 --> 01:50.750 flow. 01:50.750 --> 01:51.500 Right. 01:52.200 --> 01:59.730 Now, let us suppose that while the Joinable child thread is busy doing its own work, the parent thread 01:59.730 --> 02:02.910 invokes an API p thread underscore join. 02:03.330 --> 02:09.540 Let us suppose that this API is invoked at this particular point, which is a point called J. 02:10.140 --> 02:13.190 Let us suppose that the parent thread has invoked this p thread. 02:13.200 --> 02:20.520 Underscore join API at some point in its execution flow and let us represent that point using the letter 02:20.520 --> 02:21.040 J. 02:21.060 --> 02:21.770 Right. 02:21.780 --> 02:24.450 So this is actually a join point. 02:24.540 --> 02:29.670 Now what happens as soon as the parent thread invokes an api p thread underscore join? 02:29.700 --> 02:32.340 What is the functionality of this API? 02:32.460 --> 02:38.820 The functionality of this API is that that the parent thread gets blocked here, right? 02:39.030 --> 02:43.980 Right at the join point, the parent thread execution gets blocked. 02:45.260 --> 02:47.750 And till what time it will stay blocked. 02:47.780 --> 02:52.640 It will stay blocked until the new child thread come back and join it. 02:52.760 --> 02:53.600 Right. 02:53.780 --> 03:02.090 So it simply means that when this child thread finishes its execution, let us represent the point where 03:02.090 --> 03:04.790 it finishes its execution by a letter T. 03:04.820 --> 03:10.960 So t represents the termination point of the thread, and a child thread can choose any of the mode 03:10.970 --> 03:17.930 to terminate that is either by explicitly calling p thread underscore exit API or it simply returns 03:17.930 --> 03:19.490 from its thread function. 03:19.490 --> 03:20.300 Right. 03:20.900 --> 03:24.860 So whatever be the case when the child thread terminates. 03:26.060 --> 03:29.860 It sends a joint signal to the parent thread. 03:29.870 --> 03:30.650 Right? 03:31.340 --> 03:38.480 So it simply means that the parent thread, which was blocked at this point, will resume its execution 03:38.480 --> 03:39.130 further. 03:39.140 --> 03:39.890 Right? 03:41.090 --> 03:47.930 So note that resources of the new thread which has just terminated and join the parent thread are released 03:47.930 --> 03:53.820 only when it joins the parent thread right until the child thread joins the parent thread. 03:53.840 --> 04:01.370 The resources occupied by the child thread are not cleaned off the system and once the child thread 04:01.370 --> 04:08.300 joins the parent thread, then parent thread resumes its execution beyond the join point. 04:08.540 --> 04:11.260 So this is how Joinable thread works. 04:11.270 --> 04:18.170 The Joinable thread after its termination have to join the parent thread which is blocked on the join 04:18.170 --> 04:18.980 point. 04:19.160 --> 04:26.000 If there is no parent thread which is blocked on the join point and the child thread which is a joinable 04:26.000 --> 04:30.890 thread terminates, then the resources of the child thread would not be released. 04:30.920 --> 04:31.550 Right. 04:31.550 --> 04:37.730 So it would be wrong programming if you create a joinable thread and upon termination of the joinable 04:37.730 --> 04:47.220 thread, you do not allow the child thread to join some other thread blocked at the join point so resources 04:47.220 --> 04:52.200 of the joinable thread are not released until it joins the parent thread at the join point. 04:52.230 --> 04:57.300 A joinable thread can be converted into detached thread while it is running or vice versa. 04:57.300 --> 04:58.020 Right. 04:58.410 --> 05:05.190 So at the runtime also that is when the Joinable child thread is busy doing its work. 05:05.220 --> 05:12.090 It is also possible to change the nature of the child thread at the time when it is actually executing. 05:12.120 --> 05:16.950 The Posix standard provides certain APIs which allows you to do so. 05:17.130 --> 05:22.050 We will going to see how to use those APIs when we will be discussing demo program. 05:22.050 --> 05:28.620 And by default, if you create a new thread and you do not specify the mode of that thread, then by 05:28.620 --> 05:32.340 default the thread that is created is a joinable thread. 05:33.340 --> 05:37.720 And Joinable thread may return the result to the parent thread. 05:37.750 --> 05:40.060 Here join thread means the parent thread. 05:40.060 --> 05:40.720 Right. 05:41.390 --> 05:48.320 So this is also we will see in the demo program that how a child thread returns its result to the parent 05:48.320 --> 05:50.450 thread at the time of joining. 05:53.270 --> 05:55.940 So this was the concept of joinable threads. 05:55.940 --> 06:02.030 We will we will do an assignment on joinable threads and we will see that how joinable threads can help 06:02.030 --> 06:06.230 us to resolve certain type of multithreaded problems. 06:07.000 --> 06:07.480 Now. 06:07.480 --> 06:09.430 Next let us discuss test thread.