reliefnero.blogg.se - Wiki reader update

In this state, the structure is accessible to readers, and is therefore colored red.

Assigning a reference to this new structure to gptr transitions to the fourth and final state. Initializing this new structure transitions to the third state, which shows the initialized values of the structure's fields. Because the structure is inaccessible to readers, the updater may carry out any desired operation without fear of disrupting concurrent readers. This structure has indeterminate state (indicated by the question marks) but is inaccessible to readers (indicated by the green color). Allocating memory for a new structure transitions to the second state. The first state shows a global pointer named gptr that is initially NULL, colored red to indicate that it might be accessed by a reader at any time, thus requiring updaters to take care. The first diagram on the right depicts a four-state insertion procedure, with time advancing from left to right. This overview starts by showing how data can be safely inserted into and deleted from linked structures despite concurrent readers. A thread allocates a structure with three fields, then sets the global pointer gptr to point to this structure.Ī key property of RCU is that readers can access a data structure even when it is in the process of being updated: RCU updaters cannot block readers or force them to retry their accesses. Other names for similar techniques include passive serialization and MP defer by VM/XA programmers and generations by K42 and Tornado programmers.

The abbreviation "RCU" was one of many contributions by the Linux community. So the structure is read concurrently with a thread copying in order to do an update, hence the name "read-copy update".

once awakened by the kernel, deallocate the old structure.

sleep until the operating system kernel determines that there are no readers left using the old structure, for example, in the Linux kernel, by using synchronize_rcu(),.

update the global pointer to refer to the new structure,.

copy the data from the old structure into the new one, and save a pointer to the old structure,.

A thread wishing to do this uses the following steps: The device is available as of today.The name comes from the way that RCU is used to update a linked structure in place. The device is also relatively open to hackability thanks to its well known processor (similar to a Franklin dictionary) and easy access to the memory, but clearly OpenMoko is pointing this at people who don't even own a smartphone, not people who want to hack themselves another one. OpenMoko will have a subscription model of sorts available where folks can receive a new microSD card in the mail on a regular basis with the recent updates to the Wiki, though "power users" can update their cards themselves. The device can be searched or just browsed through clicking through interlinked articles, and there are even some parental controls to keep the chilluns away from Wikipedia's racier side.

It's a single purpose device with a monochrome screen and a simplistic touch interface and on the inside is an 8GB microSD card loaded up with three million of Wikipedia's finest hypertexts. Its first new device hardly seems to hail from the same high-end Linux places that spawned the FreeRunner, and in fact you could say the $99 WikiReader is the antitheses of a high-end smartphone. With the unfortunate downfall of the company's phone business, OpenMoko is looking for some slightly greener pastures.