Does node.js use threads/thread pool internally?
multithreading, node.js
Solution
There is no async API for file operations so node.js uses a thread pool for that. You can see it in the code of libuv.
The pool can run 4 threads:
static uv_thread_t default_threads[4];
Blocking FS tasks are posted with uv__work_submit. For example, here's how read is implemented:
int uv_fs_read(uv_loop_t* loop, uv_fs_t* req,
uv_file file,
void* buf,
size_t len,
int64_t off,
uv_fs_cb cb) {
INIT(READ);
req->file = file;
req->buf = buf;
req->len = len;
req->off = off;
POST;
}
...
#define POST \
do { \
if ((cb) != NULL) { \
uv__work_submit((loop), &(req)->work_req, uv__fs_work, uv__fs_done); \
return 0; \
} \
else { \
uv__fs_work(&(req)->work_req); \
uv__fs_done(&(req)->work_req, 0); \
return (req)->result; \
} \
} \
while (0)
If you want to implement your own threads, you can check this great introduction.
Problem
I've decided to familiarize myself with node.js and have read a several articles on the subject. What remained unclear to me is if node.js creates new threads and/or schedules tasks on threads from a thread pool when you call node.js functions. For example if I call `fs.readFile` is it executed on a different thread? If yes, [how] can I write my own function `readFileCustomized` or `doLongOperation` to run on a different thread?