Array.forEach thread safety

Question

I am using an array to store a list of connected clients.

Whenever I wish to iterate through the client list I do: clients.forEach(...).

My question is, is this thread safe, as what if a client disconnects (and is therefore removed from clients) during the a clients.forEach(...) statement?

Community · Accepted Answer · 2017-05-23 12:05:18Z

2

Short answer is yes.

forEach is a synchronous process, meaning that the array would not be modified until the process has finished executing the forEach loop on the array.

This is my understanding from reading: Are nodejs data-structures thread-safe by design?

edited May 23, 2017 at 12:05

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5 Comments

Andreas Hultgren Over a year ago

While the short answer is true, the reasoning is wrong. .forEach is synchronous and thus no other code is running at the same time.

Mallox Over a year ago

You should also mention that Node.js is single threaded and therefore threading issues can usually be ignored.

Chandu Over a year ago

what if you change the array as part of the fn you are passing to forEach ?x.forEach(function(a){console.log(a);x.push(a)}); Where x is the initial array in the scope.

Chandu Over a year ago

the statement "the array would not be modified" is not entirely true. Array can still be modified as part of the fn passed to forEach.

Trendy Over a year ago

You are correct that an array can be modified as part of the function passed to forEach, but in this specific case, the array would not be modified.

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