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ircd::ctx: Update README [skip ci]

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Jason Volk 2019-07-19 15:15:21 -07:00
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include/ircd/ctx/README.md
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@ -53,6 +53,13 @@ among others.
* The primary user object is `ircd::context` (or `ircd::ctx::context`) which has * The primary user object is `ircd::context` (or `ircd::ctx::context`) which has
an `std::thread` interface. an `std::thread` interface.
* There is no preemptive interleaving of contexts. This makes every sequence
of instructions executed a natural transaction requiring no other method of
exclusion. It also allows for introspective conditions, i.e: if context switch
occurred: refresh value, else the old value is good. This is impossible in a
preemptive environment as the result may have changed at every step during and
after the process.
### Context Switching ### Context Switching
A context switch has the overhead of a heavy function call -- a function with A context switch has the overhead of a heavy function call -- a function with
@ -77,6 +84,16 @@ asynchronous pattern. Context `A` can enqueue context `B` if it knows about `B`
and then choose whether to yield or not to yield. In any case the `io_service` and then choose whether to yield or not to yield. In any case the `io_service`
queue will simply continue to the next task which isn't guaranteed to be `B`. queue will simply continue to the next task which isn't guaranteed to be `B`.
The most common context switching encountered and wielded by developers is the
`ctx::dock`, a non-locking condition variable. The power of the dock is in its:
1. Lightweight. It's just a ctx::list; two pointers for a list head, where the
nodes are the contexts themselves participating in the list.
2. Cooperative-condition optimized. When a context is waiting on a condition
it provides, the ctx system can run the function itself to test the condition
without waking up the context.
### When does Context Switching (yielding) occur? ### When does Context Switching (yielding) occur?
Bottom line is that this is simply not javascript. There are no Bottom line is that this is simply not javascript. There are no