| 19,7 → 19,8 |
|---|
| be used even without some traditional subsystems (e.g. block devices, |
| filesystems and networking).</para> |
| |
| <figure><mediaobject id="arch1" xreflabel=""> |
| <figure> |
| <mediaobject id="arch1" xreflabel=""> |
| <imageobject role="html"> |
| <imagedata fileref="images/arch1.png" format="PNG" /> |
| </imageobject> |
| 26,12 → 27,13 |
|---|
| |
| <imageobject role="fop"> |
| <imagedata fileref="images.vector/arch1.svg" format="SVG" /> |
| </imageobject> |
| </imageobject> |
| </mediaobject> |
| |
| <title>HelenOS architecture overview.</title> |
| </figure> |
| </figure> |
| |
| <para>HelenOS is comprised of the kernel and userspace server tasks. The |
| <para>HelenOS is comprised of the kernel and the userspace server tasks. The |
| kernel provides scheduling, memory management and IPC. It also contains |
| essential device drivers that control the system clock and other devices |
| necessary to guarantee a safe environment. Userspace communicates with the |
| 44,6 → 46,10 |
|---|
| <section> |
| <title>Scheduling</title> |
| |
| <indexterm> |
| <primary>thread</primary> |
| </indexterm> |
| |
| <para>Kernel's unit of execution flow is a thread. A thread is an entity |
| that executes code and has a stack that takes up some space in memory. The |
| relation between kernel and userspace threads is 1:1:n, meaning that there |
| 50,9 → 56,11 |
|---|
| can be several pseudo threads running within one userspace thread that |
| maps to one kernel thread. Threads are grouped into tasks by functionality |
| they provide (i.e. several threads implement functionality of one task). |
| Tasks serve as containers of threads, they provide linkage to address |
| space and are communication endpoints for IPC. Finally, tasks can be |
| holders of capabilities that entitle them to do certain sensitive |
| <indexterm> |
| <primary>task</primary> |
| </indexterm> Tasks serve as containers of threads, they provide linkage |
| to address space and are communication endpoints for IPC. Finally, tasks |
| can be holders of capabilities that entitle them to do certain sensitive |
| operations (e.g access raw hardware and physical memory).</para> |
| |
| <para>The scheduler deploys several run queues on each processor. A thread |
| 80,6 → 88,10 |
|---|
| (i.e. 4-level hierarchical page tables and global page hash table), and is |
| further extensible to other mechanisms.</para> |
| |
| <indexterm> |
| <primary>address space</primary> |
| </indexterm> |
| |
| <para>Userspace tasks depend on support of address spaces provided by the |
| kernel. Each address space is a set of mutually dijunctive address space |
| areas that group pages of common attributes. An address space area is |
| 90,6 → 102,10 |
|---|
| </section> |
| |
| <section> |
| <indexterm> |
| <primary>IPC</primary> |
| </indexterm> |
| |
| <title>IPC</title> |
| |
| <para>Due to the fact that HelenOS is a microkernel, strong emphasis is |
| 103,6 → 119,24 |
|---|
| another or by sending (i.e. sharing) address space areas when larger data |
| is to be transfered.</para> |
| |
| <indexterm> |
| <primary>IPC</primary> |
| |
| <secondary>- phone</secondary> |
| </indexterm> |
| |
| <indexterm> |
| <primary>IPC</primary> |
| |
| <secondary>- answerbox</secondary> |
| </indexterm> |
| |
| <indexterm> |
| <primary>IPC</primary> |
| |
| <secondary>- message queue</secondary> |
| </indexterm> |
| |
| <para>The abstraction uses terms like phones, calls and answerboxes, but |
| is pretty similar to well-known abstraction of message queues. A task can |
| have multiple simultaneous simplex connections to several other tasks. A |