Pipes use an implicit addressing mechanism that

pipes use an implicit addressing mechanism that limits their use to
communication between related processes, typically a child process and its
parent
• a pipe() system call creates a pipe and returns two descriptors, one for each
end of the pipe
– for a simplex pipe, one descriptor is for reading, the other is for writing
– for a duplex pipe, both descriptors can be used for reading and writing
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Interprocess Communication 27
One-way Child/Parent Communication Using a Simplex Pipe
int fd[2];
char m[] = "message for parent";
char y[100];
pipe(fd); // create pipe
pid = fork(); // create child process
if (pid == 0) {
// child executes this
close(fd[0]); // close read end of pipe
write(fd[1],m,19);
...
} else {
// parent executes this
close(fd[1]); // close write end of pipe
read(fd[0],y,100);
...
}
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Interprocess Communication 28
Illustration of Example (after pipe() )
parent process
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Interprocess Communication 29
Illustration of Example (after fork() )
parent process child process
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Interprocess Communication 30
Illustration of Example (after close() )
parent process child process
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Interprocess Communication 31
Examples of Other Interprocess Communication Mechanisms
named pipe:
• similar to pipes, but with an associated name (usually a file name)
• name allows arbitrary processes to communicate by opening the same
named pipe
• must be explicitly deleted, unlike an unnamed pipe
message queue:
• like a named pipe, except that there are message boundaries
• msgsend call sends a message into the queue, msgrecv call receives the
next message from the queue
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Interprocess Communication 32
Implementing IPC
• application processes use descriptors (identifiers) provided by the kernel to
refer to specific sockets and pipes, as well as files and other objects
• kernel descriptor tables (or other similar mechanism) are used to associate
descriptors with kernel data structures that implement IPC objects
• kernel provides bounded buffer space for data that has been sent using an IPC
mechanism, but that has not yet been received
– for IPC objects, like pipes, buffering is usually on a per object basis
– IPC end points, like sockets, buffering is associated with each endpoint
P1 P2
system call
interface
system call
interface
buffer
operating system
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Interprocess Communication 33
Network Interprocess Communication
• some sockets can be used to connect processes that are running on different
machine
• the kernel:
– controls access to network interfaces
– multiplexes socket connections across the network
P2 P3
P1
network interface
P2 P3
P1
network interface
network
operating
system
operating
system
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Interprocess Communication 34
Networking Reference Models
• ISO/OSI Reference
Model
7 Application Layer
6 Presentation Layer
5 Session Layer
4 Transport Layer
3 Network Layer
2 Data Link Layer
1 Physical Layer
• Internet Model
– layers 1-4 and 7
Layer 1 Layer 1
Layer N
Layer N+1
Layer N