WEBVTT 00:04.910 --> 00:09.790 So, guys, now going forward now why threads are called lightweight process? 00:09.830 --> 00:17.090 It is to be noted that one of the most commonly termed used to address threads is a lightweight process. 00:17.180 --> 00:20.360 Threads are often called as lightweight process. 00:20.390 --> 00:23.880 Now what does this lightweight here actually means? 00:23.900 --> 00:28.160 So a thread is called a lightweight process because of the following reasons. 00:28.280 --> 00:34.670 When a thread is created, it uses almost all the pre-existing resources of the main thread. 00:34.700 --> 00:41.330 Remember, when a process is newly created, at least one thread is created and that thread is main 00:41.330 --> 00:41.980 thread. 00:41.990 --> 00:47.150 When the main thread is created, then all the necessary resources which are required for the process 00:47.150 --> 00:49.310 to exist are also created. 00:49.310 --> 00:50.060 Right. 00:50.900 --> 00:57.260 So it simply means that when a thread other than the main thread is created, it uses almost all the 00:57.260 --> 01:03.800 pre-existing resources which were created along with the main thread and hence operating system don't 01:03.800 --> 01:10.880 have to work too hard in order to create or delete an isolated execution environment of the new thread. 01:10.910 --> 01:18.050 So for example, when the main thread is created, the page table of the process is created, right? 01:18.050 --> 01:23.280 So when any other thread of the process is created, the page table need not be created again. 01:23.300 --> 01:28.790 Similarly, all the shared libraries of the process are already loaded in the main memory. 01:28.790 --> 01:29.570 Right. 01:30.290 --> 01:36.470 So these need not be loaded again in the main memory when some other new thread of the process is created. 01:36.500 --> 01:42.740 Similarly, if the process needs to communicate with some external entity via sockets, then it might 01:42.740 --> 01:45.740 be possible that the main thread has already done the job. 01:45.740 --> 01:52.390 It has already opened all the required sockets with the external entities, with which it wants to communicate. 01:52.410 --> 01:57.480 So when the new thread is created, you need not be create any new socket again. 01:57.480 --> 01:58.200 Right? 01:59.170 --> 02:02.080 Contrary to this, when a thread dies. 02:02.110 --> 02:08.200 Operating system don't have to clean up every resource used by the thread as those resources could still 02:08.230 --> 02:11.390 be in use by other threads of the same process. 02:11.410 --> 02:17.890 So example of such resources are, for example, heap memory of the process, the open sockets of the 02:17.890 --> 02:24.390 process, the open files, the inter-process communication based techniques that the process is using. 02:24.400 --> 02:31.570 So all these resources which is made available to the process need not be reclaimed back by the operating 02:31.570 --> 02:34.230 system when the thread dies, right? 02:34.240 --> 02:39.970 Because a process could be multithreaded and there could be any number of other threads which may be 02:39.970 --> 02:42.220 using these resources of the process. 02:42.640 --> 02:47.860 So operating system don't have to clean up every resource whenever the thread dies. 02:47.860 --> 02:54.040 So it simply means that operating system don't have to work too hard when a thread is created or when 02:54.040 --> 02:55.300 a thread dies. 02:55.300 --> 02:59.880 And it is for this reason that threads are called lightweight processes. 02:59.890 --> 03:00.670 Right? 03:01.360 --> 03:07.480 And finally, because threads are light weighted processes, therefore the context switching which happens 03:07.480 --> 03:13.240 between the threads which belong to the same process that is, for example, thread, t1 and thread 03:13.270 --> 03:16.780 t two are the threads that belong to the same process. 03:16.810 --> 03:23.050 Then the context switching between the threads from T1 to T2 and vice versa is called thread switching 03:23.050 --> 03:27.150 and this thread switching is faster than the process switching. 03:27.160 --> 03:31.930 Now process switching is nothing, but it is the context switching between the two threads. 03:32.290 --> 03:35.950 But these two threads belong to the different processes. 03:35.950 --> 03:36.640 Right. 03:37.240 --> 03:43.210 So note the difference between thread switching and process Switching and thread switching is way faster 03:43.210 --> 03:44.690 than process switching. 03:44.710 --> 03:51.070 So I would suggest that Google these terms and read more about these terms and understand that why thread 03:51.070 --> 03:53.350 switching is faster than process switching. 03:53.350 --> 03:56.260 The answer lies in these two points. 03:56.260 --> 03:56.920 Right? 03:57.840 --> 04:02.220 The answer lies in the fact that threads are lightweight processes.