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Description
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Correct the following program so that it correctly adds up
all of the numbers from 1 to <tt>n</tt>, where <tt>n</tt> is its command-line argument.
E.g., <tt>java Example1 100</tt> should print <tt>5050</tt>.
<p>
You will have to fix two separate problems.

Epilogue
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shown when solved

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Public permissions remove
Remarks
Comments, history, license, etc.

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Engine
Choices
json list of string, bool pairs
e.g. [["good", true], ["bad", false]]

Correct answer
Template / Reference solution

public class SumParallel {

// utility function
static void nap(int limit_ms) {
try {Thread.sleep((int)(limit_ms*Math.random()));}
catch (InterruptedException ie)
{System.out.println("!");}
}

static int total;

\[
static Lock lock = new ReentrantLock();
\show:
; // more variables?
]\

// a class that adds a number to total
static class AdderRunnable implements Runnable {
int increment;
AdderRunnable(int increment) {this.increment = increment;}
public void run() {
\[
// do nothing here
\show:
;// maybe do something here?
]\
nap(10); // random delay up to 10ms
\[
lock.lock();
\show:
;// maybe do something here?
]\
{
// increase total by increment
int oldTotal = total;
nap(2); // random delay up to 2ms
total = oldTotal + increment;
}
\[
lock.unlock();
\show:
;// maybe do something here?
]\
}
};

public static void main(String[] args) {
total = 0;

int n = Integer.parseInt(args[0]);

// keep track of all the things we execute
// & impose limit b/c using many threads at makes memory run out
ExecutorService pool = Executors.newFixedThreadPool(23);

for (int i=1; i<=n; i++)
pool.execute(new AdderRunnable(i));

\[
pool.shutdown(); // ask to shut down
while (!pool.isTerminated())
Thread.yield(); // wait until shutdown complete
\show:
pool.shutdown(); // ask to shut down
]\
System.out.println(total);
}
}

Template / Reference solution

Java test suite
See manual

testMain(100);
testMain(1000);

C++ test suite
json list of stdin/args tests
e.g. [{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]
to just run once with no input use [{}]

C++ test suite
See manual

Forbidden substrings
json list of strings
e.g. ["for","while"]

remove
Solution visibility remove
Java imports
json list of importables
e.g. ["java.util.*"]

["java.util.concurrent.*", "java.util.concurrent.locks.*"]
remove
Override Java classname
else defaults to
websheet name
remove
Dependent on other websheets?
json list of websheet names in this folder
e.g. ["DataStructure"]

remove
Is example?
i.e., just a demo
remove
Add compiler flag(s)
json list of flags
e.g. ["-Wno-unused-variable"]

remove
Remove default compiler flag(s)
json list of flags
see default_cppflags
e.g. ["-Wno-write-strings"]

remove

Property	Value
Description html markup shown to student	Correct the following program so that it correctly adds up all of the numbers from 1 to <tt>n</tt>, where <tt>n</tt> is its command-line argument. E.g., <tt>java Example1 100</tt> should print <tt>5050</tt>. <p> You will have to fix two separate problems.
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution	public class SumParallel { // utility function static void nap(int limit_ms) { try {Thread.sleep((int)(limit_ms*Math.random()));} catch (InterruptedException ie) {System.out.println("!");} } static int total; \[ static Lock lock = new ReentrantLock(); \show: ; // more variables? ]\ // a class that adds a number to total static class AdderRunnable implements Runnable { int increment; AdderRunnable(int increment) {this.increment = increment;} public void run() { \[ // do nothing here \show: ;// maybe do something here? ]\ nap(10); // random delay up to 10ms \[ lock.lock(); \show: ;// maybe do something here? ]\ { // increase total by increment int oldTotal = total; nap(2); // random delay up to 2ms total = oldTotal + increment; } \[ lock.unlock(); \show: ;// maybe do something here? ]\ } }; public static void main(String[] args) { total = 0; int n = Integer.parseInt(args[0]); // keep track of all the things we execute // & impose limit b/c using many threads at makes memory run out ExecutorService pool = Executors.newFixedThreadPool(23); for (int i=1; i<=n; i++) pool.execute(new AdderRunnable(i)); \[ pool.shutdown(); // ask to shut down while (!pool.isTerminated()) Thread.yield(); // wait until shutdown complete \show: pool.shutdown(); // ask to shut down ]\ System.out.println(total); } }
Template / Reference solution
Java test suite See manual	testMain(100); testMain(1000);
C++ test suite json list of stdin/args tests e.g. `[{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]` to just run once with no input use `[{}]`
C++ test suite See manual
Forbidden substrings json list of strings e.g. `["for","while"]`	remove
Solution visibility	remove
Java imports json list of importables e.g. `["java.util.*"]`	["java.util.concurrent.", "java.util.concurrent.locks."] remove
Override Java classname else defaults to websheet name	remove
Dependent on other websheets? json list of websheet names in this folder e.g. `["DataStructure"]`	remove
Is example? i.e., just a demo	remove
Add compiler flag(s) json list of flags e.g. `["-Wno-unused-variable"]`	remove
Remove default compiler flag(s) json list of flags see default_cppflags e.g. `["-Wno-write-strings"]`	remove

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