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Function calls are another standard kind of control flow. Surprisingly, Promela does not have function calls ! Every proctype instance is a separate process. Though if you really want, you could simulate a function call by creating a new process dynamically , and blocking until that process returns.

Verification

So far, we have determined the possible behaviors of a program simply by running the program abunch of times. For small programs, we can be very careful and make sure we exhibit all the possible traces, but the state spacesoon becomes unwieldy.

The real power of SPIN is as a tool for verification, our original goal.SPIN will search the entire state space for us , looking for (reachable) states which fail to have desired properties.

Assertions

The first verification technique we'll examine are assertion s, common to many programming languages. In Promela, the statement assert( condition ); evaluates the condition. If the result is true, execution continues as usual. Otherwise, the entire programis aborted and an error message is printed.

When simulating a single run of the program, SPIN automatically checks these run-time assertions;this is the usage that most programmers should be familiar with from traditional programming languages.But additionally, we'll see that SPIN, in the course of searching the entire state space,verifies whether an assertion can ever fail! (Though of course it can only search finite, feasible state spaces;happily,feasiblecan often include hundreds of millions of states.)

Consider our last race condition example . One of our original nave expectations was that, within each process,the value of z at the end of the process is exactly one more than at the beginning.The previous examples have shown that to be wrong, but we had to run the program until we encountered a run when it failed.Here, the assert statement puts that expectation explicitly into the program, for SPIN to check. 1 #define NUM_PROCS 3 23 show int z = 0; 45 active[NUM_PROCS] proctype increment()6 { 7 show int new_z;8 9 /* A saved copy of the old z, for the assertion. */10 show int old_z; 1112 old_z = z; 13 new_z = old_z + 1;14 z = new_z; 1516 assert(z == old_z+1); 17 }

It is often the case, as it is here, that to state the desired condition we need to add an extra variablehere, old_z . As always, it is important that when introducing such code fortesting that you don't substantially change the code to be tested, lest you inadvertently introduce new bugs!

Run this code several times, and observe when the assertion fails.This text indicates which assertion failed, and the line will be highlighted in the code window. To see which process' copy of increment failed and why, you have to look more closely at the steps shown. spin: line 16 "pan_in", Error: assertion violated spin: text of failed assertion: assert((z==(old_z+1)))

Questions & Answers

what is demand
Joseph Reply
what is mean by unitary elastic demand
Bangniyel Reply
demand is said to be unitary elastic when the percentage change in the demand is equal to the percentage change in the price
George
what is the principle of equi-marginal utility
Reliance Reply
what is Economics and it important
Anita Reply
what is production
Anita
what is Economic
Anita Reply
what is the meaning of Economic
Anita
economics is a science which studies human behaviour as a relationship between ends and scarce means which have alternative uses
Boso
I don't know.
natchanan
u don't
Ssali
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Raewyn
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Liambee
ya nyc
Ssali
Thanks kk
Anita
pls can I ask more questions
Anita
what is production
Anita
production is creation of goods and services
George
what is macroeconomics and microeconomics
Anita
macroeconomics deals with larger economic units such as GDP,GNP,employment while microeconomics deals with smaller economic units such firm and household
George
Thanks
Anita
Explain the ff Scarcity Ends Demand Supply Choice Scale of preference
Anita
macroeconomics deals with larger economic units such as GDP,GNP,employment while microeconomics deals with smaller economic units such firm and household
George
Gross Domestic product...it represent the total value of the products produced within the country including foreign industries
George Reply
what is products
Anita
what are the favourable demand
Odia Reply
list of climate that affect demands
Odia
What is two major forms of international trade?
Musa Reply
What is Economics and why it is important
Abdul Reply
De ans,Economics is the study of women behavior as a relationship between end and scared mean which have alternative uses.
Anita
What is Inflation
Abdul Reply
More money = more consumers, more consumers = lessen the product, less product = high price, high price = inflation
TuroN
is it definition
Odia
why price and quantity increase
Otuu Reply
condition under which price and quantity will be increased at the same time
Otuu
factors that hinders mobility of labour
Dennis Reply
what is scarcity
Adams Reply
why are people still unemployed in this economy we live in
Joyce Reply
why are people still unemployed in this economy
Joyce
Because of high technology
Innocent
Due to low government expenditure, the state does not have money to invest in new projects that can result in more job opportunities.
Young
good afternoon all, what are the examples of development projects Pls?
James
I 'm not together with him, when we say government expenditure mean there is recession for her economic country. That why many people still unemployed in this economy we live in, it mainly depend for two phases like Natural hazards and human activities.
Innocent
For the first answer I was responded we are concerns to intensive technology in the whole world it lead to reduce of many workers.
Innocent
wat does the abbreviation ppc mean?
Tumiso
I would like to give you ideas so that you get well how can give answer to this question dears. Attempt to know these words and what these means; Deficit, Surplus and Balanced budget.
Innocent
ppc mean pay -per-click known as search engine marketing
Innocent
i found it ppc means production possibility curve
Tumiso
in economic is that true according to your answer, however about of Marketing is that Pay Per Click.
Innocent
how is inflation, output gap relate to monetary policy
Mary Reply
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Source:  OpenStax, Model checking concurrent programs. OpenStax CNX. Oct 27, 2005 Download for free at http://cnx.org/content/col10294/1.3
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