WEBVTT 00:05.350 --> 00:07.040 So welcome back, guys. 00:07.060 --> 00:12.010 Next IPC technique that we will going to learn in this module is message queue. 00:12.640 --> 00:17.230 So in this module we will going to learn about the concepts of message queue. 00:17.260 --> 00:24.850 As an IPC, we will learn about message queue concepts, we will learn about the APIs that is provided 00:24.850 --> 00:28.740 by Linux operating system for message queue management. 00:28.750 --> 00:35.080 And then we will discuss some of the design aspects regarding how message queue should be used. 00:35.170 --> 00:38.410 And then we will wind up this module with a code walk. 00:38.920 --> 00:44.650 That is, we will going to discuss the steps to implement message queue based inter-process communication 00:44.650 --> 00:46.240 between two processes. 00:47.630 --> 00:53.720 So you can see in this diagram, this diagram essentially captures the functioning of a message queue. 00:53.750 --> 00:58.780 That is how message queue can be used to implement IPC between two processes. 00:58.790 --> 01:04.550 So we have here a process, a which is actually a sender process and is running on a Linux machine. 01:04.550 --> 01:10.160 And we have a process B which is a receiver process and is running on the same Linux machine. 01:10.430 --> 01:17.690 So you can see that between process A and process B, the channel of communication is a message queue. 01:18.200 --> 01:20.300 The process A is a sender process. 01:20.300 --> 01:26.390 That is, it can enqueue the message in the message queue and the messages are then delivered to the 01:26.390 --> 01:26.780 process. 01:26.810 --> 01:31.400 B In the same sequence in which the message was encoded by the process. 01:31.400 --> 01:38.630 A So the process of removing the message from the message queue at the other end is called DQ of a message 01:38.630 --> 01:41.930 and DQ operation is done by the receiver process. 01:41.930 --> 01:47.940 So you can see that message queue is actually a communication channel between the process A and process 01:47.970 --> 01:55.020 B, So Linux or Unix based operating systems provide another mechanism for carrying out Inter-process 01:55.020 --> 01:55.920 communication. 01:55.920 --> 01:58.620 And this mechanism is called message queue. 01:59.920 --> 02:04.690 Processes that is running on the same machine can exchange any data using message queue. 02:04.720 --> 02:11.080 So remember, message queue is a mechanism to implement IPC between processes which are running on the 02:11.080 --> 02:12.010 same machine. 02:12.040 --> 02:17.740 If the processes are running on different machines means there is no other way other than using network 02:17.740 --> 02:18.580 sockets. 02:18.910 --> 02:19.600 Right. 02:19.960 --> 02:26.230 So process can create a new message queue or can use an existing message queue which was created by 02:26.230 --> 02:27.310 another process. 02:27.760 --> 02:28.540 Right. 02:28.810 --> 02:35.320 So if the message queue is already existing message queue, then the process can actually use the existing 02:35.320 --> 02:39.730 message queue to send or receive the messages from the another process. 02:40.300 --> 02:45.730 A message queue is identified by unique ID and no two message queue can have the same ID. 02:46.060 --> 02:53.710 So within a Linux system, each message queue is assigned a unique ID, and this unique ID is actually 02:53.710 --> 02:54.880 a string. 02:56.530 --> 02:57.310 Right? 02:57.340 --> 03:02.000 So no two message queues in the system can have the same unique ID at the same time. 03:02.960 --> 03:06.980 Message queue resides and managed by the kernel and operating system. 03:06.980 --> 03:10.070 So remember message queue is a kernel resource. 03:10.070 --> 03:16.640 Kernel resource means a resource which exists inside the operating system inside the kernel. 03:16.760 --> 03:17.420 Right. 03:17.420 --> 03:21.530 So message queue resides and managed by the kernel operating system. 03:21.530 --> 03:28.430 The processes only harness or make use of the message queue which resides in the operating system. 03:28.430 --> 03:34.700 So message queue is actually a service that is provided by operating system to the userspace processes 03:34.700 --> 03:36.830 for carrying out data exchange. 03:37.930 --> 03:38.500 Right. 03:38.500 --> 03:42.760 So we say that message is just one of the kernel resource. 03:44.630 --> 03:52.100 So it's a kernel resource just like memory is one kernel resource message is another kernel resource. 03:52.490 --> 03:58.940 So sending process A can post the data to the message queue and receiving process B reads the data from 03:58.940 --> 03:59.910 the message queue. 03:59.930 --> 04:01.490 As simple as that. 04:02.480 --> 04:09.080 So the process which creates a new message queue is termed as owner or creator of the message queue.