[tankenmate]

Node's javascript engine v8 can only run in one thread, if you want to access it from a different thread you need to take a lock (for example in Chrome / Chromium you need to take an isolate lock; each page runs it's own isolated v8 engine (read only code pages are shared, all other javascript pages (data plus read/write code pages) are private); in this sense it is very similar to the GIL in Python. So although node/v8 allows for concurrency it does not allow for multi-threaded parallel execution.[0]

Because of the way tasks are scheduled in node.js you can have head of line blocking; i.e. a task that is scheduled to run first can block all the subsequent tasks, the issue that the OP suffered from. You can sometimes reduce this by calling process.nextTick(), but you need to remember that it is only IO is non-blocking in node.js.[1]

[0] https://stackoverflow.com/questions/14409609/does-the-v8-jav...

[1] http://greenash.net.au/thoughts/2012/11/nodejs-itself-is-blo...

[ysolo]

Since Google changed the V8 API to mandate use of Isolate pointers passed in to V8 functions as a parameter rather than implicitly using thread-local data for engine storage it is now possible to run separate V8 instances within the same thread (one at a time), or from different threads as they do not share state. One of the many issues Node has to contend with in using the V8 engine is a perpetually changing API surface.

[ilaksh]

See webworker-threads