Inter-process communication
(IPC)
Inter-process communication (IPC)
is a mechanism that allows processes to communicate with each other and
synchronize their actions. IPC is crucial in a multi-process, multi-threaded
environment where separate processes or threads need to share data or status
information, or coordinate their actions.
Here are some common IPC
mechanisms:
- Pipes: This is one of the simplest methods
of IPC. Data written by one process to a pipe is read by another process
reading from that pipe. Pipes are typically unidirectional but they can be
made bidirectional as well.
- Message Queues: Message queues allow
processes to exchange data in the form of messages. This is useful when
you need to transfer a moderate amount of data and there is no requirement
for immediate reading of the data.
- Shared Memory: In a shared memory model, two
or more processes can access the same segment of memory. One process can
write data to this segment, and another process can read this data
directly from memory.
- Sockets: Sockets allow communication between
processes over a network protocol. This can be used for IPC on a single
system, or for communication between processes on different systems.
- Signals: Signals are a form of software
interrupts that are sent to a process by the operating system. Signals can
be used to interrupt a process or to have it behave in a certain way.
- Semaphores: Semaphores are used to control access to shared resources by multiple processes to prevent conflicts.
Each IPC mechanism has its own
strengths and weaknesses, and the choice of which one to use depends on the
specific requirements of the system and the processes involved.
Shared Memory System and
Message Passing System.
Shared memory and message passing
are two key techniques used for Inter-Process Communication (IPC):
- Shared Memory: In the shared memory model,
two or more processes share a portion of memory. This memory space is
allocated to the processes for sharing data. One process writes data into
this shared memory and the other process can read this data directly from
there.
Shared memory can be very
efficient because it can be done at memory speeds when within a computer. Also,
it allows maximum speed and convenience of communication, as it can be done at
the speed of memory accesses.
However, it requires
synchronization, as multiple processes are reading and writing to the same
memory area. If not properly managed, it could lead to race conditions where
processes are trying to read and write simultaneously leading to inconsistency.
- Message Passing System: In the
message-passing model, the processes communicate with each other without
using shared variables. A process sends a message containing data to
another process. The sending process continues execution until the message
is sent, and the receiving process waits until it receives the message.
Message passing is a bit slower
than shared memory because it requires system calls and it needs the kernel to
transfer messages from one process to another. However, it's simpler to
implement and use than shared memory, especially in distributed systems. It's
also easier to implement in a way that avoids issues such as race conditions.
Also, message-passing systems are
easier to implement in a distributed system than shared-memory systems, because
they don't require a shared memory bus.
In general, shared memory can be
faster and more powerful but requires careful management and synchronization,
while message passing is simpler and safer but may be slower and more
resource-intensive. The choice between them depends on the specific
requirements of the system.