Let the TCP timer become expired in stead of active

[htibosch]

Description

The timer xTCPTimer is a timer that tells when the TCP engine must become active by calling xTCPTimerCheck(). In some occasions, the timer is forced to expire, for instance when recv() was called and created enough space in the reception stream: a WIN update shall be sent immediately.
However, after a certain commit to the branch IntegrationTesting1, the TCP timer was set as enabled, instead of expired.

This PR makes the following change:

-void vIPSetTCPTimerEnableState( BaseType_t xEnableState );
+void vIPSetTCPTimerExpiredState( BaseType_t xEnableState );

and

+        xTCPTimer.bActive = pdTRUE_UNSIGNED;
         if( xEnableState != pdFALSE )
         {
-            xTCPTimer.bActive = pdTRUE_UNSIGNED;
+            xTCPTimer.bExpired = pdTRUE_UNSIGNED;
         }
         else
         {
-            xTCPTimer.bActive = pdFALSE_UNSIGNED;
+            xTCPTimer.bExpired = pdFALSE_UNSIGNED;
         }

Test Steps

Send a constant stream of TCP data and look at the performance. There will be periods of inactivity.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[angelonakos]

CBMC_RETRY

[AniruddhaKanhere]

@htibosch thank you for finding the bug and the raising the PR to fix it.

I just have one question. Grateful if you can answer that.

Thanks

[AniruddhaKanhere]

If the timer is just being marked as expired, why do we need to mark it as active?
Is there any place where we will mark it as inactive thus potentially requiring the timer to be set as active again?

[htibosch]

@AniruddhaKanhere wrote:

If the timer is just being marked as expired, why do we need to mark it as active?

Because when a timer is inactive, it will be ignored by the function prvIPTimerCheck():

static BaseType_t prvIPTimerCheck( IPTimer_t * pxTimer )
{
    BaseType_t xReturn;

    if( pxTimer->bActive == pdFALSE_UNSIGNED )
    {
        /* The timer is not enabled. */
        xReturn = pdFALSE;
    }
    else

and so prvIPTimerCheck() will never see the expired flag :-(

Is there any place where we will mark it as inactive thus potentially requiring the timer to be set as active again?

The flag bActive is set during every call to vIPSetTCPTimerExpiredState(), while nobody will ever clear it. It would be enough to set it once at start-up.

At the other hand, that would require a new function vIPSetTCPTimerEnableState() and an extra function-call at start-up, and one more unit test... without a measurable performance gain.