Introduction
Inter-process communication (IPC) refers to the mechanisms provided by an operating system that allow processes to exchange data and coordinate their actions. Applications typically use IPC by functioning as clients (requesting data) and servers (responding to requests). In distributed computing, many processes act as both clients and servers.
IPC plays a critical role in microkernels and nanokernels, which minimize kernel functionality. These systems rely heavily on IPC to communicate with external servers, significantly increasing message exchanges compared to monolithic kernels. IPC interfaces typically include analytical frameworks and structured communication procedures to ensure compatibility across multi-vector protocols.
IPC can be synchronous or asynchronous. Synchronization primitives can be used to create synchronous behavior even when an asynchronous IPC mechanism is used.
Inter-Process Communication Techniques
Pipes
Pipes provide a half-duplex (one-way) communication channel between two related processes. One process writes data into the pipe, and another process reads from it—similar to filling and emptying a bucket.
Shared Memory
Shared memory allows multiple processes to access a common memory region. Communication occurs when one process updates the shared memory and other processes read the changes.
The classic example is the Producer–Consumer problem:
- The Producer generates items.
- The Consumer consumes items.
- A shared buffer holds the items.
The problem may be:
- Unbounded buffer – unlimited buffer size.
- Bounded buffer – buffer has a fixed capacity.
In the bounded buffer case, the producer must stop when the buffer is full, and the consumer must wait when it is empty.
Message Passing
Message passing allows processes to communicate without shared memory. Two processes create a communication link and exchange messages using primitives such as:
- send(message, destination)
- receive(message, source)
Messages may be fixed-size or variable-size. Each message typically consists of a header (containing type, source, destination, length, and control information) and a body. Messages are usually delivered in FIFO order.
Message Queues
Message queues store messages in a linked list inside the kernel. Each queue is identified using a unique message queue identifier.
Direct Communication
In direct communication, processes explicitly name each other. A link must exist between communicating processes, and every pair of processes must establish a (usually bidirectional) communication link.
Indirect Communication
Processes communicate via mailboxes or ports. The sender places a message in a mailbox, and the receiver retrieves it. Links may be uni- or bi-directional.
FIFO
FIFO (named pipes) allow full-duplex communication between two unrelated processes. Process P1 can communicate with P2 and vice versa.
Reasons to Use Inter-Process Communication
- Improves modularity and system organization
- Supports computational efficiency
- Allows separation of privileges
- Enhances communication and synchronization between applications
- Enables multiple operating system components to coordinate their actions
Advantages of IPC
- Enables one application to control or communicate with another
- Supports shared data exchange through semaphores, memory segments, and other mechanisms
- Efficient message transfer between processes
- Reduces blocking issues found in other communication methods
- Enables parallel execution of tasks by dividing programmes into independent modules
- Makes maintenance and debugging easier due to modular design
- Supports multitasking such as editing, compiling, and audio playback simultaneously
Disadvantages of IPC
- Pipe communication may have a fixed data size limit
- Message queues have an upper limit on total data size
- Shared memory requires processes to avoid writing to the same location simultaneously
- Synchronization and memory protection issues may arise
- Slower than direct function calls
- Risk of data corruption if memory access is not properly managed
Applications of IPC
- Exchange of data among multiple threads or processes
- Synchronization of actions between cooperating processes
- Critical in microkernel and nanokernel operating system design
- Useful in designing applications composed of multiple cooperating components
- Supports distributed computing and multi-process applications