Message passing - Revision history

Amallen: updated this page to reflect new receive and recvclr functions

2008-06-23T22:21:18Z

updated this page to reflect new receive and recvclr functions

Amallen: made changes to reflect the discovery that "send" is actually non-blocking

2008-06-23T22:05:52Z

made changes to reflect the discovery that "send" is actually non-blocking

Amallen: New page: Message passing is one method used by XINU threads for interprocess communication. It allows threads to send individual messages to other threads by using the system calls send 2008-06-09T22:25:01Z New page: Message passing is one method used by XINU threads for interprocess communication. It allows threads to send individual messages to other threads by using the system calls <code>send</code... New page Message passing is one method used by XINU threads for interprocess communication. It allows threads to send individual messages to other threads by using the system calls <code>send</code> and <code>receive</code>. Each thread has memory allocated for a single message in its thread control block specifically for messages sent and received using this method. This form of message passing should not be confused with the [[mailbox]] messaging queue system also used for interprocess communication. Upon creation, each thread is allocated memory in its thread control block for two fields which apply to this message passing system: a 4 byte (<code>int</code> type) message box to contain a single message sent to this thread, and a one byte flag (<code>bool</code> type) to signal if there is an unreceived message waiting in that thread's message box. Threads use the functions <code>send(tid_typ tid, int msg)</code> and <code>receive(bool block)</code> to utilize this system of message passing. <code>send(tid_typ tid, int msg)</code> delivers the message passed in as the parameter <code>msg</code> to the message box in the thread control block of the thread with a thread id of <code>tid</code>, also passed in as a parameter. <code>send</code> is always blocking and will always reschedule if the receiving thread was in a state of waiting to receive a message (<code>THRRECV</code>). <code>receive(bool block)</code> returns the message waiting in the message box of the thread control block of the thread which called <code>receive</code>. If there is no message waiting for the thread then one of two things will happen depending on if the <code>receive</code> call was blocking or non-blocking. If it was blocking then the thread will go into a state of waiting to receive a message (<code>THRRECV</code>) until a message is passed to the thread. If it was non-blocking then <code>receive</code> will simply return NULL signifying that there was no message waiting for the thread.

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-Message passing is one method used by XINU threads for interprocess communication. It allows threads to send individual messages to other threads by using the system calls <code>send</code> and <code>receive</code>. Each thread has memory allocated for a single message in its thread control block specifically for messages sent and received using this method. This form of message passing should not be confused with the [[mailbox]] messaging queue system also used for interprocess communication.
+Message passing is one method used by XINU threads for interprocess communication. It allows threads to send individual messages to other threads by using the system calls <code>send</code>, <code>receive</code>, and <code>recvclr</code>. Each thread has memory allocated for a single message in its thread control block specifically for messages sent and received using this method. This form of message passing should not be confused with the [[mailbox]] messaging queue system also used for interprocess communication.
 Upon creation, each thread is allocated memory in its thread control block for two fields which apply to this message passing system: a 4 byte (<code>int</code> type) message box to contain a single message sent to this thread, and a one byte flag (<code>bool</code> type) to signal if there is an unreceived message waiting in that thread's message box.
-Threads use the functions <code>send(tid_typ tid, int msg)</code> and <code>receive(bool block)</code> to utilize this system of message passing.
+Threads use the functions <code>send(tid_typ tid, int msg)</code>, <code>receive()</code>, and <code>recvclr()</code> to utilize this system of message passing.
 <code>send(tid_typ tid, int msg)</code> delivers the message passed in as the parameter <code>msg</code> to the message box in the thread control block of the thread with a thread id of <code>tid</code>, also passed in as a parameter. <code>send</code> will always yield the processor by calling reschedule if the receiving thread was in a state of waiting to receive a message (<code>THRRECV</code>).
-<code>receive(bool block)</code> returns the message waiting in the message box of the thread control block of the thread which called <code>receive</code>. If there is no message waiting for the thread then one of two things will happen depending on if the <code>receive</code> call was blocking or non-blocking. If it was blocking then the thread will go into a state of waiting to receive a message (<code>THRRECV</code>) until a message is passed to the thread. If it was non-blocking then <code>receive</code> will simply return NULL signifying that there was no message waiting for the thread.
+<code>receive()</code> returns the message waiting in the message box of the thread control block of the thread which called <code>receive</code>. If there is no message waiting for the thread then the thread will go into a state of waiting to receive a message (<code>THRRECV</code>) until a message is passed to the thread.