Bài giảng Interprocess Communication môn Nguyên lý hệ điều hành | Trường Đại học Công nghệ, Đại học Quốc gia Hà Nội

Operating Systems Phan Xuan Hieu
Data Science & Knowledge Technology Lab Faculty of IT, VNU-UET hieupx@vnu.edu.vn Interprocess Communication Materials § Textbook:
• A. Silberschatz, P. B. Galvin, and G. Gagne: Operating System Concepts,
10th edition, John Wiley & Sons, 2018. • Chapter 3 § Futher reading:
• A. S. Tanenbaum and H. Bos: Modern Operating Systems, 4th edition, Pearson Prentice Hal , 2015. • Chapter 2 3 Contents
§ Interprocess communication (IPC)
§ IPC in shared-memory systems
§ IPC in message-passing systems § Examples of IPC systems 4 Contents
§ Interprocess communication (IPC)
§ IPC in shared-memory systems
§ IPC in message-passing systems § Examples of IPC systems 5 Interprocess communication
§ Processes within a system may be independent or cooperating
§ Cooperating process can affect or be affected by other processes, including data
§ Reasons for cooperating processes: • Information sharing • Computation speedup • Modularity • Convenience
§ Cooperating processes need interprocess communication (IPC) § Two models of IPC • Shared memory • Message passing 6 Communication models Shared memory Message passing 7 Producer-consumer problem
§ Paradigm for cooperating processes:
• Producer process produces information that is consumed by a consumer process § Two variations:
• Unbounded-buffer places no practical limit on the buffer size: • Producer never waits
• Consumer waits if there is no data in the buffer to consume
• Bounded-buffer assumes that there is a fixed buffer size
• Producer must wait if the buffer is full
• Consumer waits if there is no data in the buffer to consume 8 Contents
§ Interprocess communication (IPC)
§ IPC in shared-memory systems
§ IPC in message-passing systems § Examples of IPC systems 9 IPC – shared memory
§ An area of memory shared among the processes that wish to communicate
§ The communication is under the control of the user
processes, not the operating system
§ Major issue is to provide mechanism that wil al ow the
user processes to synchronize their actions when they access shared memory
§ Synchronization is discussed in detailed in later lectures 10
Bounded-buffer shared-memory solution § Shared data #define BUFFER_SIZE 10 typedef struct { . . . } item; item buffer[BUFFER_SIZE]; int in = 0; int out = 0;
§ Solution is correct, but can only use BUFFER_SIZE-1 elements 11
Producer process (shared memory) item next_produced; while (true) {
/* produce an item in next produced */
while (((in + 1) % BUFFER_SIZE) == out); /* do nothing */
buffer[in] = next_produced;
in = (in + 1) % BUFFER_SIZE; } 12
Consumer process (shared memory) item next_consumed; while (true) {
while (out == in); /* do nothing */
next_consumed = buffer[out];
out = (out + 1) % BUFFER_SIZE;
/* consume the item in next consumed */ } 13
What about using al the buffer?
§ Suppose that we want a solution to the producer-
consumer problem that can use al the buffer.
§ We can do so by having an integer counter that keeps
track the current number of elements in the buffer.
§ Initial y, counter is set to 0.
§ The integer counter is incremented by the producer
after it produces a new element.
§ The integer counter is decremented by the consumer after it consumes an element. 14 Producer process while (true) {
/* produce an item in next produced */
while (counter == BUFFER_SIZE); /* do nothing */
buffer[in] = next_produced;
in = (in + 1) % BUFFER_SIZE; counter++; } 15 Consumer process while (true) {
while (counter == 0); /* do nothing */
next_consumed = buffer[out];
out = (out + 1) % BUFFER_SIZE; counter--;
/* consume the item in next consumed */ } 16 Race condition
§ counter++ could be implemented as • register1 = counter
• register1 = register1 + 1
• counter = register1
§ counter-- could be implemented as • register2 = counter
• register2 = register2 – 1
• counter = register2
§ Consider if execution interleaving with “counter = 5” initial y:
• S0: producer executes register1 = counter (register1 = 5)
• S1: producer executes register1 = register1 + 1 (register1 = 6)
• S2: consumer executes register2 = counter (register2 = 5)
• S3: consumer executes register2 = register2 – 1 (register2 = 4)
• S4: producer executes counter = register1 (counter = 6)
• S5: consumer executes counter = register2 (counter = 4) 17 Race condition (cont.) § Why race condition?
§ How to deal with race condition?
Wil be discussed in detailed in later lecture. 18 Contents
§ Interprocess communication (IPC)
§ IPC in shared-memory systems
§ IPC in message-passing systems § Examples of IPC systems 19 IPC – message passing
§ Processes communicate with each other without resorting to shared variables
§ IPC facility provides two operations:
• send(message)
• receive(message)
§ The message size is either fixed or variable 20