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In JS, "global variable" means "property of the global object". No reference to "process". It's trivial to have a single-process JS application with multiple

In JS, "global variable" means "property of the global object". No reference to "process". It's trivial to have a single-process JS application with multiple JS global objects in it. Case in point: any web browser (and renderer processes don't change this: every iframe on a page has a separate global object). It's just that Node _chose_ to reuse the same global object for multiple requests instead of using a clean execution environment. I have to agree with jessedhillon: that sounds insane.

jessedhillon 15y ago
I have to amend my previous statement, these guys are right. I created this Python script here https://gist.github.com/1329943 https://gist.github.com/1329943 and ran it. If global context were not shared, then each request would receive a new random number, but they don't. Each request gets the same number. Even without doing this experiment, the result is obvious. There would have to be some meta process to start new interpreter processes here in order to prevent the same environment from being reused. Since that is not the case, because you have to invoke the python interpreter manually here, you cannot get multiple distinct results. (Theoretically, in this code, you could get two different responses if they both entered the `if ... is None` clause in send_head() before one of the requests could cause the global variable to be set.)
- bzbarsky 15y ago
  You're running your whole server in python. So yes, there is only one process and its globals are very much global. Note that you are NOT writing some program that embeds the python interpreter and then runs it on python code of your choice. In the case of Node, it's embedding V8. It can in fact run JS code of its choice in an environment of its choice, set up new globals, etc.
isntitvacant 15y ago
(I assume) the reason that node chose to go with a single global object (which is optional[0]) is that JS gets a bit hinky when dealing with multiple contexts: e.g., an array returned from a function defined in a different context will not satisfy `[] instanceof Array`, since the receiving module's instance of `Array` is not strictly equal to to called module's copy of `Array`. In practice, this problem is why you see `Array.isArray`, `jQuery.isArray`, `_.isArray` and friends so often -- they exist to give a canonical, non-"check if any member of X's inheritance chain matches Y.prototype" way to determine if a given instance is actually an array. So, in summation: yes, it's weird that Node has this, but ultimately it's a lesser-vilified problem of JavaScript's. [0]: https://github.com/joyent/node/blob/master/lib/module.js#L51 https://github.com/joyent/node/blob/master/lib/module.js#L51 -- `NODE_MODULE_CONTEXTS=1 node <file.js>` will run separate modules in separate global contexts.
- bzbarsky 15y ago
  Thanks for the pointer to NODE_MODULE_CONTEXTS!

jessedhillon 15y ago

I have to amend my previous statement, these guys are right. I created this Python script here https://gist.github.com/1329943 https://gist.github.com/1329943 and ran it. If global context were not shared, then each request would receive a new random number, but they don't. Each request gets the same number. Even without doing this experiment, the result is obvious. There would have to be some meta process to start new interpreter processes here in order to prevent the same environment from being reused. Since that is not the case, because you have to invoke the python interpreter manually here, you cannot get multiple distinct results. (Theoretically, in this code, you could get two different responses if they both entered the `if ... is None` clause in send_head() before one of the requests could cause the global variable to be set.)

bzbarsky 15y ago
You're running your whole server in python. So yes, there is only one process and its globals are very much global. Note that you are NOT writing some program that embeds the python interpreter and then runs it on python code of your choice. In the case of Node, it's embedding V8. It can in fact run JS code of its choice in an environment of its choice, set up new globals, etc.

isntitvacant 15y ago

(I assume) the reason that node chose to go with a single global object (which is optional[0]) is that JS gets a bit hinky when dealing with multiple contexts: e.g., an array returned from a function defined in a different context will not satisfy `[] instanceof Array`, since the receiving module's instance of `Array` is not strictly equal to to called module's copy of `Array`. In practice, this problem is why you see `Array.isArray`, `jQuery.isArray`, `_.isArray` and friends so often -- they exist to give a canonical, non-"check if any member of X's inheritance chain matches Y.prototype" way to determine if a given instance is actually an array. So, in summation: yes, it's weird that Node has this, but ultimately it's a lesser-vilified problem of JavaScript's. [0]: https://github.com/joyent/node/blob/master/lib/module.js#L51 https://github.com/joyent/node/blob/master/lib/module.js#L51 -- `NODE_MODULE_CONTEXTS=1 node <file.js>` will run separate modules in separate global contexts.

bzbarsky 15y ago
Thanks for the pointer to NODE_MODULE_CONTEXTS!