CODEWITHSUNDEEP
javascriptnode.jsipcchild-processspawn
Warmduscher
Warmduscher

Reputation: 11

node.js second spawned child process doesn't receive stdin messages

I have an event in my node.js script which need to be called multiple times that spawns a child process. Not parallel just one child process at the time.

    var child = spawn('node', [script, arg1],{cwd: "./", stdio:  ["pipe","pipe","pipe","ipc"]})

I need to send messages to that child process. With the first spawned process it works just fine with:

      child.stdin.write("my_message")//also tried child.stdin.write("my_message\n")

The listener on the spawned script looks like that:

process.stdin.on("data", async(data)=> {
    //dosomething
    process.exit();
 }

But when the first child process is done and closed and the second child process is spawned the child.stdin.write("my_message") doesn't reach the child process.

I thought there is a problem with the stdtin channel not closing when the child process exited. So I tried process.stdin.end(); on the child process and all the following functions on the child.on("close") and child.on("exit") events

child.on("close", (data)=>{

console.log("Child process closed")
//child.stdin.end();
//child.stdout.end();
//child.stdin.destroy();
//child.kill("SIGINT");
//child = undefined;
//child.disconnect();
//child.ref(); })

I also tried sending messages trough ipc. But this throws 'ERR_IPC_CHANNEL_CLOSED' when trying to send a message to the second spawned child.

node --version v14.17.5

Upvotes: 0

Views: 855

Answers (1)

Warmduscher
Warmduscher

Reputation: 11

Outsourcing the function that spawns the child processes and the associated listeners in an external module actually worked. Not sure why.

//spawnChild.js
module.exports = function(arg1){

   var child = spawn('node', [script, arg1],{cwd: "./", stdio:  ["pipe","pipe","pipe","ipc"]})

   //plus the unmodified child.stderr, child.stdout... listeners in here
}

Calling the new module in the main script with:

var childProcess = require("./spawnChild.js")(arg1)

Upvotes: 1

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