Each process has its own address space. Even if the addresses in the two processes have the same value, they actually point to different locations. Inter-process communication typically takes place through the operating system's common area.
Threads in the same process can communicate directly because they belong to the same address space.
It is not only an entity that operates independently within the system, but also an entity that independently competes for resources.
Threads are also known as light-weight processes. Threads of the same process share global variables and memory, making it easy and convenient for threads to share data, but it will cause mutual exclusion of some shared data.
Many programs are written using threads to increase efficiency.
The derivation of parent-child processes is very expensive, and the communication between parent-child processes needs ipc or other methods to implement, which is troublesome. The creation of threads costs much less, and threads in the same process share global storage, so communication is convenient.
The disadvantages of threads are also caused by its advantages, mainly synchronization, asynchronous, and mutual exclusion issues. It is worthwhile to design carefully when using them.
Only the processes need to communicate with each other. The threads of the same process share the address space. There is no need for communication, but the synchronization/mutex mutex must be used to protect the shared global variables. The thread has its own stack. Synchronization/mutual exclusion is the primitive primitives.
Regardless of the signal between the processes, the pipeline pipe or the shared memory is guaranteed by the operating system and is a system call.
Inter-thread communication: Since multiple threads share address space and data space, communication between multiple threads is one thread of data can be directly provided to other threads without having to go through the operating system (that is, the kernel's scheduling).
Communication between processes is different. The independence of its data space determines that its communication is relatively complex and needs to pass through the operating system. In the past, communication between processes was only a stand-alone version. Operating systems now inherit socket-based inter-process communication mechanisms. In this way, communication between processes is not limited to a single computer, and network communication is realized.
First, the method of communication between processes
Pipe: A pipe is a half-duplex communication method. Data can only flow in one direction and can only be used between related processes. The kinship of a process usually refers to the parent-child process relationship.
Namedpipe: A named pipe is also a half-duplex communication method, but it allows communication between unrelated processes.
Semaphore: A semaphore is a counter that can be used to control the access of multiple processes to shared resources. It is often used as a locking mechanism to prevent a process from accessing a shared resource when other processes access it. Therefore, it is mainly used as a synchronization method between processes and between different threads in the same process.
Messagequeue: A message queue is a linked list of messages stored in the kernel and identified by a message queue identifier. Message queuing overcomes the shortcomings of less signaling information, the ability of the pipeline to carry only unformatted byte streams, and the limited buffer size.
Signal (sinal): Signal is a more complex method of communication used to inform the receiving process that an event has occurred.
Shared memory: Shared memory is a memory mapped to a memory that can be accessed by other processes. This shared memory is created by one process but accessible by multiple processes. Shared memory is the fastest IPC method. It is specially designed for the low efficiency of communication between other processes. It is often used in conjunction with other communication mechanisms, such as signals, to achieve synchronization and communication between processes.
Socket: Socket is also an inter-process communication mechanism. Unlike other communication mechanisms, it can be used to communicate between different processes.
Second, the communication between threads
Locking mechanisms: including mutex locks, condition variables, and read-write locks * Mutexes provide exclusive ways to prevent data structures from being modified concurrently. * Read-write locks allow multiple threads to read shared data at the same time, and are mutually exclusive with write operations. * Condition variables can block processes atomically until a particular condition is true. The test of the condition is performed under the protection of the mutual exclusion lock. Condition variables are always used with mutexes.
Semaphore: Include unnamed thread semaphores and named thread semaphores
Signal: signal processing between similar processes
The purpose of communication between threads is mainly for thread synchronization, so threads have no communication mechanism for data exchange like process communication.
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