Differences among pipes, pipe passes and pipe States

The Conduit 、 Tube side 、 Difference of tube state

Sum up the comparison

	purpose	nature
Tube side	Used for process synchronization	A data structure , It is convenient for us to manage a series of semaphores , At the same time, encapsulate the semaphore operation
The Conduit pipe	For process communication	pipe The communication of is based on the file system , that pipe It's actually a file , We passed this document IO To indirectly realize the communication between processes
Tube state	Control the permissions of the process	PCB One of the signs , Used to confirm the permission status of the current process

Learn from others' articles ：

Tube side

（ Process synchronization ） Centralize shared variables and all operations that can be performed on shared variables in one module , An operating system or concurrent program is composed of several such modules , Because a module is usually short , The connection between modules is clear , Improved readability , Easy to maintain and modify , Correctness is easy to guarantee .

The Conduit

（ Process of communication also socket、 mail 、 Semaphore 、 Shared memory 、 Message queue, etc ）
The so-called pipeline , It is an open shared file connected between two processes , Dedicated to data communication between processes . The sending process can continuously write data streams from one end of the pipeline , The length of each write is variable ; The receiving process can read data from the other end of the pipe when needed , The readout unit length is also variable . obviously , The foundation of pipeline communication is file system .

Tube state

Tube state ( The system state ) V.S Eye state （ User mode ）

CPU Alternate between operating system programs and user programs .

CPU The status of belongs to the program status word PSW One of . Most computer systems will CPU The execution status is divided into pipe status and target status .
Tube state is also called privilege state , System state or nuclear state of mind .CPU The complete set of instruction system can be executed in tube state . Usually , The operating system runs in tube mode .

Target state is also called normal state or user state . When the machine is in target state , The program can only execute non privileged instructions . The user program can only run in the target state , If the user program executes the privilege instruction in the target state , The hardware will interrupt , Controlled by the operating system , Privileged instruction execution is prohibited , This can prevent the user program from damaging the system intentionally or unintentionally .

The only way to change from the target state to the tube state is to interrupt .

From the pipe state to the target state can be achieved by modifying the program status word , This will be accompanied by the conversion from operating system programs to user programs .