Child-process-promise

How does child process work?
What is child_process module?
What is the difference between child_process and spawn?
Why do we create child processes?
Why are child processes used?
Can we create child processes in node applications?
What is the output in the child process?
What is the difference between exit and close in node child_process?
How do I create a child process in Linux?
What is the difference between child process exec and execSync?
What is spawn vs fork?
What is the difference between process nextTick () and setImmediate ()?
Should I use fork or spawn NodeJS?
What is the difference between spawn and execFile?
Does child process wait for parent?
Does child process run first?
Does parent or child process go first?
How does a child process terminate?
Does parent and child process have same pid?
Can parent and child processes run concurrently?
Can a process have two parents?
What does if PID == 0 mean?
How many child processes are created?
Do child processes inherit open files?

How does child process work?

A child process inherits most of its attributes, such as file descriptors, from its parent. In Unix, a child process is typically created as a copy of the parent, using the fork system call. The child process can then overlay itself with a different program (using exec) as required.

What is child_process module?

The child_process module provides us with utility functions whose logics are stacked on top of one another. The most basic function is spawn() : Docs: spawn. The spawn function will spawn a new process of git log type.

What is the difference between child_process and spawn?

spawn is best used to when you want the child process to return a large amount of data to Node - image processing, reading binary data etc. child_process. spawn is "asynchronously asynchronous", meaning it starts sending back data from the child process in a stream as soon as the child process starts executing.

Why do we create child processes?

A child process is a process created by a parent process in operating system using a fork() system call. A child process may also be called a subprocess or a subtask. A child process is created as its parent process's copy and inherits most of its attributes.

Why are child processes used?

We can easily spin a child process using Node's child_process module and those child processes can easily communicate with each other with a messaging system. The child_process module enables us to access Operating System functionalities by running any system command inside a, well, child process.

Can we create child processes in node applications?

js provides the fork() function, a variation of spawn() , to create a child process that's also a Node. js process. The main benefit of using fork() to create a Node. js process over spawn() or exec() is that fork() enables communication between the parent and the child process.

What is the output in the child process?

The read end of one pipe serves as standard input for the child process, and the write end of the other pipe is the standard output for the child process.

What is the difference between exit and close in node child_process?

the short version is, 'exit' emits when the child exits but the stdio are not yet closed. 'close' emits when the child has exited and its stdios are closed.

How do I create a child process in Linux?

A new process can be created by the fork() system call. The new process consists of a copy of the address space of the original process. fork() creates new process from existing process. Existing process is called the parent process and the process is created newly is called child process.

What is the difference between child process exec and execSync?

The primary difference here is execSync which would be blocking and exec would be non-blocking. execSync blocks the creating process until the child_process created using execSync returns. exec immediately returns and will return a value if there is one later on and won't block the creating parent process.

What is spawn vs fork?

Forking and spawning are two different start methods for new processes. Fork is the default on Linux (it isn't available on Windows), while Windows and MacOS use spawn by default. When a process is forked the child process inherits all the same variables in the same state as they were in the parent.

What is the difference between process nextTick () and setImmediate ()?

It is interesting to note that setImmediate adds callbacks to the event queue that are executed during the check phase, whereas process. nextTick executes callbacks immediately after the current phase.

Should I use fork or spawn NodeJS?

Spawn is useful when you want to make a continuous data transfer in binary/encoding format — e.g. transferring a 1 Gigabyte video, image, or log file. Fork is useful when you want to send individual messages — e.g. JSON or XML data messages.

What is the difference between spawn and execFile?

The major difference between spawn() and exec() / execFile() is that stdin for the spawned process can be configured, and stdout and stderr are Readable streams in the parent process. This means exec() and execFile() must complete before you can read the buffer outputs.

Does child process wait for parent?

A call to wait() blocks the calling process until one of its child processes exits or a signal is received. After child process terminates, parent continues its execution after wait system call instruction. Child process may terminate due to any of these: It calls exit();

Does child process run first?

The original process is called the parent process and the second process is called the child process. The child process is an almost exact copy of the parent process. Both processes continue executing from the point where the fork( ) calls returns execution to the main program.

Does parent or child process go first?

The goal is to run the child process first. In short, the logic behind it is that if the child is ran first, the overhead of copy on write (COW) is eliminated if the child is calling exec since the parent does not have any chance to write to the address space.

How does a child process terminate?

A child process may be terminated if its parent process requests for its termination. A process can be terminated if it tries to use a resource that it is not allowed to. For example - A process can be terminated for trying to write into a read only file. If an I/O failure occurs for a process, it can be terminated.

Does parent and child process have same pid?

The child process has a unique process ID (PID) that does not match any active process group ID. The child has a different parent process ID, that is, the process ID of the process that called fork(). The child has its own copy of the parent's file descriptors.

Can parent and child processes run concurrently?

The child process is created and runs concurrently with the parent. In this case, as soon as process creation is successful, the process manager replies to the parent, and the child is made READY. If it's the parent's turn to run, then the first thing it does is return from the process-creation function.

Can a process have two parents?

No. By definition of what we understand as parent process, it's the process that spawned the child process. One process has to do that. And that's the parent.

What does if PID == 0 mean?

The if (PID == 0) evaluates the return value. If PID is equal to zero then printf() is executed in the child process, but not in the parent process. The else part of the condition is executed in the parent process and the child process but only the parent process will execute the else part of the condition.

How many child processes are created?

Explanation: If there are n fork() calls, then number of child processes created are 2ⁿ – 1.

Do child processes inherit open files?

* The child inherits copies of the parent's set of open file descriptors. Each file descriptor in the child refers to the same open file description (see open(2)) as the corresponding file descriptor in the parent.