Subversion Repositories HelenOS-doc

        <listitem>

        <listitem>

          <para>Notification queue</para>

          <para>Notification queue</para>

        </listitem>

        </listitem>

      </itemizedlist>

      </itemizedlist>

      <para>The communication between task A, that is connected to task B

      <para>The communication between task A, that is connected to task B

      looks as follows: Task A sends a message over it's phone to the target

      looks as follows: Task A sends a message over it's phone to the target

      asnwerbox. The message is saved in task B incoming call queue. When task

      asnwerbox. The message is saved in task B incoming call queue. When task

      B fetches the message for processing, it is automatically moved into the

      B fetches the message for processing, it is automatically moved into the

      dispatched call queue. After the server decides to answer the message,

      dispatched call queue. After the server decides to answer the message,

      immediately closed. The client connection identification (phone id) is

      immediately closed. The client connection identification (phone id) is

      not reused, until the client issues closes it's own side of the

      not reused, until the client issues closes it's own side of the

      connection ("hangs his phone up").</para>

      connection ("hangs his phone up").</para>

      <para>When a task dies (whether voluntarily or by being killed), cleanup

      <para>When a task dies (whether voluntarily or by being killed), cleanup

      <orderedlist>

      <orderedlist>

        <listitem>

        <listitem>

          <para>Hangs up all outgoing connections and sends hangup messages to

          <para>Hangs up all outgoing connections and sends hangup messages to

          all target answerboxes.</para>

          all target answerboxes.</para>

      <para>On top of this simple protocol the kernel provides special

      <para>On top of this simple protocol the kernel provides special

      services closely related to the inter-process communication. A range of

      services closely related to the inter-process communication. A range of

      method numbers is allocated and protocol is defined for these functions.

      method numbers is allocated and protocol is defined for these functions.

      The messages are interpreted by the kernel layer and appropriate actions

      The messages are interpreted by the kernel layer and appropriate actions

      <para>The kernel provides the following services:</para>

      <para>The kernel provides the following services:</para>

      <itemizedlist>

      <itemizedlist>

        <listitem>

        <listitem>

      functionality. To open a new outgoing connection, the client sends a

      functionality. To open a new outgoing connection, the client sends a

      <constant>CONNECT_ME_TO</constant> message using any of his phones. If

      <constant>CONNECT_ME_TO</constant> message using any of his phones. If

      the recepient of this message answers with an accepting answer, a new

      the recepient of this message answers with an accepting answer, a new

      connection is created. In itself, this mechanism would allow only

      connection is created. In itself, this mechanism would allow only

      duplicating existing connection. However, if the message is forwarded,

      duplicating existing connection. However, if the message is forwarded,

      <para>On startup every task is automatically connect to the name service

      <para>On startup every task is automatically connect to the name service

      task, which acts as a switchboard and forwards requests for connection

      task, which acts as a switchboard and forwards requests for connection

      to specific services. To be able to forward a message it must have a

      to specific services. To be able to forward a message it must have a

      phone connected to the service tasks. The task creates this connection

      phone connected to the service tasks. The task creates this connection

      asks name service task to create a callback connection.</para>

      asks name service task to create a callback connection.</para>

      <para>Tasks can share their address space areas using IPC messages. The

      <para>Tasks can share their address space areas using IPC messages. The

      2 message types - AS_AREA_SEND and AS_AREA_RECV are used for sending and

      2 message types - AS_AREA_SEND and AS_AREA_RECV are used for sending and

      receiving an address area respectively. The shared area can be accessed

      receiving an address area respectively. The shared area can be accessed

    </section>

    </section>

  </section>

  </section>

  <section>

  <section>

    <title>Userspace view</title>

    <title>Userspace view</title>

      <emphasis>manager</emphasis> task is found or a new one is created and

      <emphasis>manager</emphasis> task is found or a new one is created and

      control is transfered to this manager task. The manager tasks pops

      control is transfered to this manager task. The manager tasks pops

      messages from the answerbox and puts them into appropriate queues of

      messages from the answerbox and puts them into appropriate queues of

      running tasks. If a task waiting for a message is not running, the

      running tasks. If a task waiting for a message is not running, the

      control is transferred to it.</para>

      control is transferred to it.</para>

      <para>Very similar situation arises when a task decides to send a lot of

      <para>Very similar situation arises when a task decides to send a lot of

      messages and reaches kernel limit of asynchronous messages. In such

      messages and reaches kernel limit of asynchronous messages. In such

      situation 2 remedies are available - the userspace liberary can either

      situation 2 remedies are available - the userspace liberary can either

      cache the message locally and resend the message when some answers

      cache the message locally and resend the message when some answers