libuv-internals is a collection of simple code snippets which represent different parts of the libuv architecture. For example the queue snippet shows how QUEUE works with a simple use-case.

QUEUE is a circularly linked list in libuv which is used to store tasks in order. Its main idea is to have a array with two items. The first item points to the previous list node while the second points to the next one. The last node points again to the beginning of the list. Through this set up it is possible by just following the pointers to navigate through the list. If you now want to access a specific queue member you can calculate the memory address of the struct which implements a queue node as property. This is possible because a struct is always saved in one memory block and the position of a property has a specific byte offset. Using this allows to create a pointer to the beginning of the whole struct and we can access other properties.

To avoid blocking libuv executes work requests in a thread pool. Each time intensive i/o should be done a task will be put in queue and then spawned as thread in which it can execute to the end without blocking the main thread. The given examples show up basic thread management. It is recommend to read this document to get an idea of the basics.

There are several mechanisms which are used by libuv to handle pending tasks in a non-blocking way. For example async.c uses eventfd (on linux) and else socketpair to execute async callbacks. Also all notification for example about new readable data in the socket must be published to libuv somehow. The events section tries to get some concepts of that.

The stream component is the most platform dependent part of libuv. As I understood correctly so far the most simple implementation works by just subscribing to a file discriptor with the event notification system of the os. In case of OS X this is not possible for all all file discriptor types. This causes libuv to create an extra thread polling manuelly the file state and then using the async component to wake up the main thread. The created example tries to the main idea of a readable file stream which will execute read callbacks each time new data is added to the file.

Copyright © 2013 Bodo Kaiser [email protected]

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