WEBVTT 00:05.230 --> 00:11.530 So, guys, now next we will going to discuss the mutex locking so the way we lock and unlock the mutex 00:11.530 --> 00:14.870 can be divided or can be categorized into two categories. 00:14.890 --> 00:20.110 The first category is called code locking, and the second category is called object locking. 00:20.230 --> 00:25.690 So let us discuss these two ways of locking and unlocking the mutex in a little bit detail. 00:26.050 --> 00:33.700 So if you need to protect a code snippet, that is a portion of the code of your program against concurrent 00:33.730 --> 00:37.300 thread, unsafe access, then we will go for code locking. 00:37.390 --> 00:44.800 And if you need to protect an object against concurrent thread unsafe access, then we go for object 00:44.800 --> 00:45.460 locking. 00:45.460 --> 00:46.060 Right? 00:46.060 --> 00:51.760 So at this point of time, these two lines may not make much sense to you, so let us discuss the code 00:51.760 --> 00:54.490 locking and object locking with the help of an example. 00:55.450 --> 00:58.000 So let us discuss the code locking first. 00:58.030 --> 01:06.460 So let us suppose that you have a file dot C, and in this file you have taken a mutex object which 01:06.460 --> 01:07.960 is global within this file. 01:07.960 --> 01:08.560 Right? 01:08.590 --> 01:14.950 The scope of this object is within this file because the declaration of this object is guarded by this 01:14.950 --> 01:16.000 static keyword. 01:16.000 --> 01:16.690 Right? 01:17.770 --> 01:22.210 Now, the question is that why we have taken this mutex global variable in this file? 01:22.870 --> 01:29.350 The answer is that that using this global mutex object, we can protect all the critical sections which 01:29.350 --> 01:30.690 are present in this file. 01:30.700 --> 01:31.360 Right? 01:31.360 --> 01:34.900 So, for example, this is the critical section in this file. 01:34.900 --> 01:37.150 There could be more critical section in this file. 01:37.180 --> 01:42.910 But for example, let us consider that there is only one critical section in this file in the function 01:42.910 --> 01:50.380 foo and we guard or protect this critical section against concurrent unsafe thread access by sandwiching 01:50.380 --> 01:53.650 this critical section between mutex, lock and mutex. 01:53.650 --> 01:55.580 Unlock APIs right. 01:56.780 --> 02:02.210 So it would simply means that at most one thread can execute inside this critical section. 02:02.240 --> 02:06.500 Now, why we are saying that this type of locking is a code locking. 02:06.530 --> 02:12.800 The reason is that that just by looking at the code as a programmer or developer, you can very well 02:12.800 --> 02:17.630 identify that this particular region of the code is a critical section. 02:17.840 --> 02:21.830 So in code locking mutex are defined in the source file level. 02:21.830 --> 02:27.440 That is, we have this mutex which is defined as a global variable within this file and we use this 02:27.440 --> 02:30.320 mutex object to protect all the critical sections. 02:30.320 --> 02:36.080 So let us take an example to understand this code locking so you can see the code on the right hand 02:36.110 --> 02:43.580 side, we have a global buffer, which is a global object or global variable within this file, right? 02:45.250 --> 02:50.830 And let us suppose that inside this file you have taken a global mutex object, right? 02:51.520 --> 02:57.640 Now, if you analyze this function packet received, you will see that in this function we are making 02:57.640 --> 03:02.380 use of this global variable that is global buffer, right? 03:02.380 --> 03:07.990 So it simply means that these three lines of code of this function is a critical section. 03:08.140 --> 03:15.160 If this function that is packet receive is accessed by thread t one thread t two, then this global 03:15.160 --> 03:21.820 buffer will be written and accessed in a thread unsafe manner by the two threads t1 and t2 thread. 03:21.820 --> 03:28.450 Unsafe manner means the thread t one and t two will perform write write operation over this global buffer 03:28.450 --> 03:30.760 which are conflicting operations. 03:32.430 --> 03:38.430 So here you can see that as a programmer or developer, just by looking at the code, you can very well 03:38.430 --> 03:43.350 say that these three lines forms the critical section, right? 03:43.980 --> 03:50.250 So it would simply means that you need to sandwich these three lines of code between pthread mutex lock 03:50.250 --> 03:51.420 and pthread mutex. 03:51.420 --> 03:52.680 Unlock calls. 03:53.590 --> 04:00.760 So when you use a mutex to actually protect a code fragment, we call this type of locking as code locking. 04:00.760 --> 04:01.480 Right?