commit
b240cff0ff
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@ -11,6 +11,14 @@
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|||
course: tfe4130
|
||||
desc: Bølgeforplantning, våren 2021.
|
||||
updated: 2021-01-12
|
||||
-
|
||||
course: ttk4145
|
||||
desc: Sanntidsprogrammering, våren 2021.
|
||||
updated: 2021-05-04
|
||||
-
|
||||
course: tiø4252
|
||||
desc: Teknologiledelse, våren 2021.
|
||||
updated: 2021-05-04
|
||||
|
||||
# Høsten 2020
|
||||
-
|
||||
|
|
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|||
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@ -2,6 +2,7 @@
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|||
<script src="{{ "/assets/js/jquery-3.5.1.min.js" | relative_url }}"></script>
|
||||
<script src="{{ "/assets/js/bootstrap.bundle.min.js" | relative_url }}"></script>
|
||||
<script src="{{ "/assets/js/bootstrap-toc.min.js" | relative_url }}"></script>
|
||||
|
||||
<!--Anchors-->
|
||||
<script src="{{ "/assets/js/anchor.min.js" | relative_url }}"></script>
|
||||
<script>
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||||
|
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@ -10,4 +11,4 @@
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|||
icon: '#',
|
||||
};
|
||||
anchors.add('h1, h2, h3, h4, h5').remove('.no-anchor');
|
||||
</script>
|
||||
</script>
|
||||
|
|
|
|||
|
|
@ -0,0 +1,63 @@
|
|||
---
|
||||
title: TIØ4252
|
||||
description: Teknologiledelse, våren 2021
|
||||
date: 2021-05-13
|
||||
---
|
||||
|
||||
|
||||
## Formelark
|
||||
|
||||
Kommer straks.
|
||||
|
||||
## Eksamen
|
||||
|
||||
Alle filer er tilgjengelig på [git][git].
|
||||
|
||||
[git]: https://git.glados.no/oyvindskaaden/TIO4252
|
||||
|
||||
Kombinert løsningsforslag for alle eksamener finnes [her][LF_alle].
|
||||
|
||||
[LF_alle]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/LF.pdf
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||||
|
||||
| År | Eksamen | Oppgave | LF |
|
||||
| :--- | :------ | :------------ | :------- |
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||||
| 2020 | Høst | [Oppgave][1] | [LF][2] |
|
||||
| 2020 | Sommer | [Oppgave][3] | [LF][4] |
|
||||
| 2020 | Vår | [Oppgave][5] | [LF][6] |
|
||||
| 2019 | Høst | [Oppgave][7] | [LF][8] |
|
||||
| 2019 | Sommer | [Oppgave][9] | [LF][10] |
|
||||
| 2018 | Høst | [Oppgave][11] | [LF][12] |
|
||||
| 2018 | Sommer | [Oppgave][13] | [LF][14] |
|
||||
| 2018 | Vår | [Oppgave][15] | [LF][16] |
|
||||
| 2017 | Høst | [Oppgave][17] | [LF][18] |
|
||||
| 2017 | Vår | [Oppgave][19] | [LF][20] |
|
||||
| 2014 | Sommer | [Oppgave][21] | [LF][22] |
|
||||
| 2013 | Sommer | [Oppgave][23] | [LF][24] |
|
||||
{: .table-responsive-lg .table }
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||||
|
||||
[1]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20H/Eksamen_20H.pdf
|
||||
[2]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20H/Losning_20H.pdf
|
||||
[3]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20S/Eksamen_20S.pdf
|
||||
[4]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20S/Losning_20S.pdf
|
||||
[5]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20V/Eksamen_20V.pdf
|
||||
[6]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20V/Losning_20V.pdf
|
||||
[7]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19H/Eksamen_19H.pdf
|
||||
[8]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19H/Losning_19H.pdf
|
||||
[9]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19S/Eksamen_19S.pdf
|
||||
[10]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19S/Losning_19S.pdf
|
||||
[11]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18H/Eksamen_18H.pdf
|
||||
[12]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18H/Losning_18H.pdf
|
||||
[13]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18S/Eksamen_18S.pdf
|
||||
[14]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18S/Losning_18S.pdf
|
||||
[15]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18V/Eksamen_18V.pdf
|
||||
[16]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18V/Losning_18V.pdf
|
||||
[17]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17H/Eksamen_17H.pdf
|
||||
[18]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17H/Losning_17H.pdf
|
||||
[19]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17V/Eksamen_17V.pdf
|
||||
[20]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17V/Losning_17V.pdf
|
||||
[21]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/14S/Eksamen_14S.pdf
|
||||
[22]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/14S/Losning_14S.pdf
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||||
[23]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/13S/Eksamen_13S.pdf
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||||
[24]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/13S/Losning_13S.pdf
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@ -0,0 +1,376 @@
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|||
---
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||||
title: "Oppsumering av TTK4145"
|
||||
description: "Lot of theory and discussion, some fomulas, spring 2021."
|
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date: 2021-05-04
|
||||
math: true
|
||||
---
|
||||
|
||||
## Fault tolerance
|
||||
|
||||
Hard to capture faults.
|
||||
|
||||
|
||||
### Bugs
|
||||
|
||||
* 1 bug per 50 lines before testing
|
||||
* 1 bug per 500 at release
|
||||
* 1 bug per 550 after a year, the constant
|
||||
|
||||
1. Make the program work within specs.
|
||||
2. Run/Tests of the program-
|
||||
3. Errors happen
|
||||
4. Locate errors
|
||||
* Incomplete spec
|
||||
* Missing handleling of som situation
|
||||
5. Fix code
|
||||
|
||||
### Traditional error handeling
|
||||
|
||||
{% highlight c %}
|
||||
FILE *
|
||||
openConfigFile(){
|
||||
FILE * f = fopen("/path/to/config.conf");
|
||||
if (f == NULL) {
|
||||
switch(errno){
|
||||
case ENOMEM: {
|
||||
...
|
||||
break;
|
||||
}
|
||||
case ENOTDIR: {
|
||||
...
|
||||
break;
|
||||
}
|
||||
// Do this for all errors
|
||||
}
|
||||
}
|
||||
}
|
||||
{% endhighlight %}
|
||||
|
||||
### Causes of errors
|
||||
|
||||
* Incomplete specification
|
||||
* Software bugs
|
||||
* HW problems
|
||||
* Communication problems
|
||||
|
||||
### Fault tolerance in real time systems
|
||||
|
||||
The problem with traditional errorhandleing is that errors can happen at any possible time.
|
||||
This is extremely hard to test.
|
||||
|
||||
This is some of the error handling real time programming have.
|
||||
|
||||
* Handling of unexpected errors
|
||||
* More threads hanles errors
|
||||
* Can not test the conventional way
|
||||
* Can only show extistence of errors
|
||||
* Can not find errors in specification
|
||||
* Can not find race conditions
|
||||
|
||||
The fault path is shown under.
|
||||
|
||||
|
||||
|
||||
With fault tolerance the path looks something more like the figure under.
|
||||
|
||||
|
||||
|
||||
### Error handling
|
||||
|
||||
Keep it simple!
|
||||
|
||||
The error modes is a part of the module interface.
|
||||
|
||||
One way is to handle all errors the same way.
|
||||
Handle the as if it was the worst error.
|
||||
Crash and start again.
|
||||
|
||||
A different approach is to check that everything is OK.
|
||||
|
||||
To test how the systems responds for a unknown error is to insert a failed acceptance test (a not OK signal).
|
||||
|
||||
### Redundancy
|
||||
|
||||
* If I have $N$ copies of my data, it is possible to handle that one is destroyed.
|
||||
* Sending $N$ messages, trying $N$ times.
|
||||
|
||||
**Static redundancy**
|
||||
|
||||
* $N$ active copies. Sending $N$ messages if it is necessary or not.
|
||||
* Detecting errors is not important.
|
||||
* Handles cosmic rays easily.
|
||||
|
||||
**Dynammic redunancy**
|
||||
|
||||
* Relies on detecting the error and recovering
|
||||
* Resend if timeout and not receiving "ack"
|
||||
* Go with default if no messages have been received
|
||||
* The acceptancetest must be good.
|
||||
|
||||
|
||||
### Fault model
|
||||
|
||||
#### Example with storage functions.
|
||||
|
||||
**Step 1: Failure modes**
|
||||
|
||||
Find the failure modes: What could go wrong?
|
||||
|
||||
* **Write**: May return "I failed". Does not know why it faield
|
||||
* **Read**: May return "I failed". Does not know why it failed.
|
||||
|
||||
**Step 2: Detect, Simplify, Inject errors**
|
||||
|
||||
* Write information on where/what/how the process is doing.
|
||||
* All errors --> Fail
|
||||
* Inject errors
|
||||
|
||||
**Step 3: Handling with redundancy**
|
||||
|
||||
* Have multiple copies of the the information
|
||||
* Use only the newest
|
||||
|
||||
#### Example with communication function
|
||||
|
||||
**Step 1: Failure modes**
|
||||
|
||||
* Message
|
||||
* Lost
|
||||
* Delayed
|
||||
* Corrupted
|
||||
* Duplicated
|
||||
* Wrong recipient
|
||||
|
||||
**Step 2: Detection, Merging of errormodes and error injection**
|
||||
|
||||
* Adding information to message
|
||||
* Checksum
|
||||
* Session ID
|
||||
* Sequence number
|
||||
* Adding "ack" on well recieved messages
|
||||
* All errors will be treaded as "Lost message"
|
||||
* Injection
|
||||
* Occasionally throw away some messages
|
||||
|
||||
**Step 3: Handling with redundancy**
|
||||
|
||||
* Timeout
|
||||
* Retransmit message
|
||||
|
||||
#### Example with processes and caculations
|
||||
|
||||
A calculation is an abstract, so how can we talk generally about the failure modes.
|
||||
|
||||
**Step 1: Failure modes**
|
||||
|
||||
One failure mode
|
||||
|
||||
**Step 2: Detect, simplify, inject errors**
|
||||
|
||||
All failed acceptance tests will "PANIC" or "STOP".
|
||||
|
||||
**Step 3: Handling with redundancy**
|
||||
|
||||
There are three solutions:
|
||||
|
||||
1. Checkpoint restart
|
||||
* Do all the work incuding the acceptance test
|
||||
* Wait with the "side effects"
|
||||
* Store a checkpoint
|
||||
* Do the "side effects"
|
||||
2. Process pairs
|
||||
* Crash and let an another process take over
|
||||
3. Presistent processes
|
||||
|
||||
|
||||
## Transactions
|
||||
|
||||
A transaction is a design framework for Damage Confinement and Error Recovery.
|
||||
|
||||
* An *atomic action*, just without the backward recovery error mode as standard mode
|
||||
* invincible and instantaneous "calculation" seen from the outside
|
||||
* A transformation from one consistent state to another'
|
||||
* A modular computation
|
||||
|
||||
### Four features: ACID
|
||||
|
||||
* **A**tomicity: Either all side effects happens or none
|
||||
* **C**oncistency: Leaves the system in a consistent state when finished
|
||||
* **I**solation: Errors does not spread
|
||||
* **D**urability: Results are not lost
|
||||
|
||||
### Atomic Actions
|
||||
|
||||
**Resumption vs. Termination mode**
|
||||
* If we continue where we were (e.g. after the interrupt) --> *Resumption*
|
||||
* If we continue somewhere else (i.e. terminating what we where doing) --> Termination
|
||||
|
||||
**Async Notification (AN) = Low level thread interaction**
|
||||
* Async event handling. ("Signals") (resumption)
|
||||
* Modeled after a HW interrupt
|
||||
* Can be sent to the correct thread
|
||||
* Can be handled, ignored, blocked --> The domain can be controlled.
|
||||
* Often lead to polling
|
||||
* Could rather skip the signal and poll a status variable or a message queue
|
||||
* Useless
|
||||
* ATC --> Async transfer of Control (termination)
|
||||
* Canceling threads
|
||||
* setjmpt/longjmp could convert signals to ATC (not really, but still)
|
||||
* ADA: a strictured mechanism for ATV is integraded with the selected statement
|
||||
* RT Java: A structured mechanism for ATC is integraded with the exception-handling mechanism
|
||||
|
||||
#### Cancelling threads
|
||||
|
||||
**Yes, killing threads is ATC!**
|
||||
|
||||
* Can make termination model by letting domain be a thread
|
||||
* "Create a `doWork` thread, and kill it if the action fails"
|
||||
* Ca still control domain by disabling "cancelstate"
|
||||
|
||||
**But, but, but: It leaves ut in undifined state!?**
|
||||
* Not if we have...
|
||||
* Full control over changed state (like logs or recovery points) or some other way of recovering well.
|
||||
* A lock manager that can unlock on behalf of killed thread
|
||||
* Some control of where we were killed (like nok in the middle of a lock manager or log call)
|
||||
* An this is what we have!
|
||||
|
||||
|
||||
## Shared variable synchronization
|
||||
|
||||
### Non-Preemptive scheduling
|
||||
|
||||
Controlling a pump filling a tank.
|
||||
|
||||
**Spec:**
|
||||
* Every second: measure the water level of the tank and generate the reference to the pump
|
||||
* 10 times a second: Set the power of the pump motor
|
||||
* Do some GUI: let the human control the process
|
||||
|
||||
#### A trivial solution: "Cyclic Exectutive"
|
||||
|
||||
{% highlight c %}
|
||||
oldTime = now();
|
||||
i = 0;
|
||||
while(true) {
|
||||
i = i + 1;
|
||||
if (i % 10 == 0) {
|
||||
i = 0;
|
||||
calculatePumpReference();
|
||||
}
|
||||
controlPump();
|
||||
do {
|
||||
handleUserEvent();
|
||||
} while(now() < oldTime + 0.1);
|
||||
oldTime = oldTime + 0.1;
|
||||
}
|
||||
{% endhighlight %}
|
||||
|
||||
**Drawbacks**
|
||||
|
||||
* OK tasks?
|
||||
* Timing hard to tune (what if pump sampling should be $\pi$/10?)
|
||||
* Overload (what if `calucaltePumpReference` uses more than 1/10 seconds?)
|
||||
* How to add new tasks? (Everything is coupled)
|
||||
* Waste of time in the do-loop?
|
||||
* What is priority of `handleUserEvents`?
|
||||
* How are erros, exceptions, alarms etc. handled?
|
||||
|
||||
#### Better soulution with Non-preemptive scheduler
|
||||
|
||||
* *3 taskts* administered by a scheduler
|
||||
* The scheduler takes care of who runs and timing
|
||||
* Scheduler often inculuded in OSes
|
||||
* Introducing priorities
|
||||
|
||||
{% highlight c %}
|
||||
/**
|
||||
* scheduler_registerThread(function, time, priority)
|
||||
* Higher priority numer means higher priority in scheduler
|
||||
*/
|
||||
main() {
|
||||
scheduler_registrerThread(controlPump, 0.1, 3);
|
||||
scheduler_registrerThread(calculatePumpReference, 1, 2);
|
||||
scheduler_registrerThread(handleUserEvents, 0.2, 1);
|
||||
scheduler_mainLoop();
|
||||
}
|
||||
{% endhighlight %}
|
||||
|
||||
**Some notes on priorities**
|
||||
* Priority is generally not important; rather, the main rule is to give higher priority to shorter-deadline tasks.
|
||||
* This allows tasks to reach its deadlines.
|
||||
* ... but this is not always the case - if e.g. the tasks are cooperating
|
||||
* We still handle overload badly
|
||||
* And: What connection between deadline and priority to start with?
|
||||
* Is this a good dependency seen from a code quality perspective?
|
||||
|
||||
### Pros and cons of nonpreemptive scheduling
|
||||
|
||||
| **Pros** | **Cons** |
|
||||
| :--------------------------------------------- | :------------------------------------------------------------------------- |
|
||||
| Simple, intuitive, predictable | C macro hell |
|
||||
| No kernel | Threads must cooperate <-- a form of dependency breaking module boundaries |
|
||||
| Fast switching times | Heavy threads must be divided |
|
||||
| Some elegant sunchronization patterns possible | Can we handle blocking of library functions? |
|
||||
| | Unrobust to errors |
|
||||
| | Unrobust to (heavy) error handling |
|
||||
| | Hard to tune at end of project |
|
||||
{: .table-responsive-lg .table }
|
||||
|
||||
|
||||
|
||||
### Preemptive Kernel
|
||||
|
||||
* Preemption, thread objects and the timer interrupt
|
||||
* Enabling synchronization: Busy waiting, tes-and-set, disabling the timer interrupt
|
||||
* Blocking and suspend & resume
|
||||
* An API for synchronization? Semaphores!
|
||||
|
||||
|
||||
#### Preemption
|
||||
|
||||
* Make a handler for a timer interrupt
|
||||
* Store all registers (including IP & SP) in a "thread object"
|
||||
* Organize queue of processes (Round Robin e.g. - a collection of thread objects?)
|
||||
* Can synchronize by: while(!ready); (busy wating, "spin locks")
|
||||
|
||||
**Bad solution**
|
||||
|
||||
{% highlight c%}
|
||||
while(lock==1) {}
|
||||
lock = 1;
|
||||
// We may run
|
||||
lock = 0;
|
||||
{% endhighlight %}
|
||||
|
||||
**Better solution**
|
||||
|
||||
{% highlight c%}
|
||||
void t1() {
|
||||
flag1 = 1; // Declare my intention
|
||||
turn = 2; // But try to be polite
|
||||
while(flag2 == 1 && turn == 2) {}
|
||||
// We may run
|
||||
flag1 = 0;
|
||||
}
|
||||
{% endhighlight %}
|
||||
|
||||
##### Looking more closely at the arsenal
|
||||
|
||||
**How can we make basic synchronization under preemption?**
|
||||
|
||||
* Spin locks (wasting time and cpu)
|
||||
* Test&Set (swap) assembly instruction (atomic, but not obvious)
|
||||
* Disable interrupt (steals control from OS/scheduler)
|
||||
|
||||
**But**
|
||||
* If we disable the timer interrupt we don not have preemption any more
|
||||
* And... Are these good abstractions in the application programmer domain?
|
||||
|
||||
#### Blocked threads
|
||||
|
||||
**Let us introduce another queue; the collection of threads not running, waiting for something**
|
||||
|
||||
* Fixes the bad performance of spin locks. Is conceptually better.
|
||||
* "Suspend" moves a thread object from "run" queue to "blocked" queue
|
||||
* "Resume" moves it back.
|
||||
|
||||
|
|
@ -0,0 +1,15 @@
|
|||
---
|
||||
layout: layouts/list
|
||||
title: "TTK4145"
|
||||
description: "Sanntidsprogrammering"
|
||||
---
|
||||
|
||||
## Oppsummering
|
||||
|
||||
[Oppsummering](summary/) av faget TTK4145.
|
||||
|
||||
## Prosjekt
|
||||
|
||||
## Øvinger
|
||||
|
||||
|
||||
Loading…
Reference in New Issue