Await and async

I was working on an project that was using the async and await keywords and an college asked what/why use the await/ async keywords when you will still be waiting on the task / thread to finish. Which was an very good question, and the best answer that I could give (of which I am writing it here) is that if you want to start an thread and let it process it’s work whilst still carrying on with the main thread then you would need to write some thread controls etc. But .Net gives you that thread control with the async / await keywords.

The async is short for asynchronous which basically means do something whilst doing something else, e.g. you are able to talk and listen at the same time!.

So what happens is that you can create an method to do some long processing, I am just using an Task delay here to simulate that with also using the await syntax just before it so that it will actually wait for the task delay to finish, as below

 public async Task<Boolean> getCheckAsync(Boolean c)
        {
            System.Console.WriteLine("getCheckAsync about to wait");
            await Task.Delay(1000);
            System.Console.WriteLine("getCheckAsync finished waiting");
            // do some processing.. pulling data from a database / website etc.
            if (c)
                return false;
            else
                return true;
        }

You have to decorate the method call with async Task, since then you will be able to do some await on this method.

The next part is to create an call to this method, and this will start the call as well — start processing the method of getCheckAsync

 Task<Boolean> getCheckAsyncTask = this.getCheckAsync(t);            // calls the process to start processing -- e.g. will output "getCheckAsync about to wait"

And to await for the result, which means that you are able to do some other actions in between the calling the method (getCheckAsync) and waiting on the result.

Boolean res = await getCheckAsyncTask;

So from the full code example below, the first output would be

Calling the async
Waiting for result from getCheckAsync
getCheckAsync about to wait
Bit inbetween the getCheckAsync call

which as you can see has already called the getCheckAsync method and then carried on processing the bit inbetween that is not reliant on the result of the method call (getCheckAsync), but once we are ready for the result of the getCheckAsync method call, the output would carry on with

getCheckAsync finished waiting
Obtainted the result from getCheckAsync
Passed the 'Calling the async'
B = False

Here is the code in full

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace asynctest
{
    class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
 
            System.Console.WriteLine("Calling the async ");
 
            Boolean b = p.getCheck(true).Result; 
 
            System.Console.WriteLine("Passed the 'Calling the async'");
            System.Console.WriteLine("B = "+b);
            System.Console.ReadLine();
        }
 
        public async Task<Boolean> getCheck(Boolean t)
        {
            System.Console.WriteLine("Waiting for result from getCheckAsync ");
            Task<Boolean> getCheckAsyncTask = this.getCheckAsync(t);            // calls the process to start processing -- e.g. will output "getCheckAsync about to wait"
            System.Console.WriteLine("Bit inbetween the getCheckAsync call");   // do some extra processing.
            Boolean res = await getCheckAsyncTask;                              // but now we have to "await" for the result.
            System.Console.WriteLine("Obtainted the result from getCheckAsync ");
            return res;
        }
 
        public async Task<Boolean> getCheckAsync(Boolean c)
        {
            System.Console.WriteLine("getCheckAsync about to wait");
            await Task.Delay(1000);
            System.Console.WriteLine("getCheckAsync finished waiting");
            // do some processing.. pulling data from a database / website etc.
            if (c)
                return false;
            else
                return true;
        }
 
    }
}

vectors and for_each

A friend of mine asked how to use the newer for_each and is it similar to the foreach in php, so here is the example that I gave and thus doing it online as well.

To start with the foreach (php version here) does loop over data and so does the for_each in c++, but the main difference is that the for_each in c++ is basically a for loop

for (; first!=last;++first)
   functionCall(*first);

where the functionCall is the parameter passed in to do something with that part of the data.

The great thing with c++ is that you are able to use either a method, structure etc as long as it is able to output a variable then we are good.

So here is a example, please note that I am loading up a vector e.g. only functions that have a single int make sense.

void printNumber (int i) {
	cout << "Print the number from a function : " << i << "\n";
}
 
for_each(v.begin(), v.end(), printNumber);

here we are using the for_each (where the v is a vector) passing in the start and end of the vector with a function as the last parameter.

and here

// create a object that can use the operator() to output value passed in.
struct structToOutput {
	void operator() (int i) {
		cout << "Struct to output : " << i << "\n";
	}
} structToOutputObject;
 
for_each(v.begin(), v.end(), structToOutputObject);

will output the values differently but in essence still able to access the values.

Here is the code in full

#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
void printNumber (int i) {
	cout << "Print the number from a function : " << i << "\n";
}
 
// create a object that can use the operator() to output value passed in.
struct structToOutput {
	void operator() (int i) {
		cout << "Struct to output : " << i << "\n";
	}
} structToOutputObject;
 
int main(int argc, char* argv[])
{
	// lets load up some dummy data.
	vector<int> v;
	for (int i =0; i< 10; i++)
		v.push_back(i);
 
	// run through the vector using a standard function with parameter
	for_each(v.begin(), v.end(), printNumber);
	// output using a operator() method
	for_each(v.begin(), v.end(), structToOutputObject);
	return 0;
}

with the output being

Print the number from a function : 0
Print the number from a function : 1
Print the number from a function : 2
Print the number from a function : 3
Print the number from a function : 4
Print the number from a function : 5
Print the number from a function : 6
Print the number from a function : 7
Print the number from a function : 8
Print the number from a function : 9
Struct to output : 0
Struct to output : 1
Struct to output : 2
Struct to output : 3
Struct to output : 4
Struct to output : 5
Struct to output : 6
Struct to output : 7
Struct to output : 8
Struct to output : 9

How to compile with g++

g++ <filename> -o <outfilename> -std=c++11

auto and lambda

The C++ 11 standards are starting to take more and more cue’s from other languages where you are able to create functions on the fly (lambda). With also adding the “auto” keyword which will allow the program to automatically figure out what type of variable will be returned from lambda function.

So here the break up of the lambda function is

<return type> <[optional local variables to be used]>(optional parameters);

The optional local variables are abit like the “use” within PHP (use)

So the full code is

#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
int main(int argc, char* argv[])
{
	int num = 30;
	int anothernum = 0;
 
	auto func = [&anothernum](int i) {
			cout << "Parameter passed in :" << i << "\n";
			anothernum = anothernum + 10; // alter the value passed in.
			return 50;	// return a value and use the auto keyword.
	};
	int ret = func(num);
	cout << "Return from func :" << ret << "\n";
	cout << "Another num :" << anothernum << "\n";
	return 0;
}

and the output would be

Parameter passed in : 30
Return from func : 50
Another num : 10;

To compile with g++ I used these parameters

g++ <filename> -o <outfilename> -std=c++11

Lambda

After allot of coding of late, thought that I would place online a great syntax called lambda which allows you to do assign functions to a variable that is callable!!. So the functions like pref_replace_callback that has a function as the parameter to be used if any matches are meet.

So for a example, I think that source code always works the best.

function newFun ($name) { 
	$call = function ($second) use ($name) {
		return $second . $name; 
	};
	return $call($name);
 
}
 
echo newFun("hi there");

and the output would be

hi therehi there

What it is doing is assigning to the $call variable is the actual function call! which is able to be able to pass in via the parameters a parameter but also to “use” local variables within the function. The $name is passed in to the newFun function and is then use[d] within the lambda function, how cool is that!.

PHP – function use

As with the previous post about the use method within php (here), you are also able to use the use method attached to a callable function as in

function ($parameter) USE ($somevalue)

So you are able to use any variables that are within scope within the new function, below is an example where I am using the array walk methods callback (which means call a function that is available). The function is using the values within the array ($arrays 4 and 5) and adding them to the $value variable that is passed within the use parameters (here I am using the & symbol which means to pass in reference and not just a copy of the value (you are able to alter the actual parameter passed), so in this instance the $value starts of with 1, then adds 4 and then 5 to it which in turn the result is 10.

$value = 1;
$callback = function ($one) use (&$value) {
	$value += $one;
};
$arrays = array(4,5);
array_walk($arrays, $callback);
print_r("value : " .$value);

And the output would be.

value : 10

WFC Soap class within an class communicating with PHP

Within the Windows Foundation Classes you are able to create SOAP end points. These end points you are able to communicate using classes funny enough (because of the WFC being classes). But to communicate with these is fine with PHP and also when you sometimes have a class within an class as a parameter passing to the SOAP end point. Well you are able to do it within PHP as well.

If you have a WFC service and add these to the service for the ServiceContract and create the DataContract’s and DataMembers

[ServiceContract]
public interface IService1
{
    [OperationContract]
    string NewValue(NewName name);
}
 
[DataContract]
public class SecondName
{
    int svalue1;
    int svalue2;
 
    [DataMember]
    public int Svalue1
    {
        get { return svalue1; }
        set { svalue1 = value; }
    }
 
    [DataMember]
    public int Svalue2
    {
        get { return svalue2; }
        set { svalue2 = value; }
    }
}
 
[DataContract]
public class NewName
{
    SecondName secondValue = new SecondName();
 
    [DataMember]
    public SecondName SecondValue
    {
        get { return secondValue; }
        set { secondValue = value; }
    }
}

Created the SecondName class as the second named class with the svalue1/2 within in turn the NewName named class will reference the SecondName class.

And then within the class that implements the interface here is the function name to call within the soap end point called NewValue.

public string NewValue(NewName namesec)
{
    return string.Format("Value : {0}", namesec.SecondValue.Svalue1 + namesec.SecondValue.Svalue2);
}

Well to find out what you need to pass to the soap call I was using an WFC application to write out the debugging information with altering the web.config by

    <system.serviceModel>
      <diagnostics>
        <messageLogging
             logEntireMessage="true"
             logMalformedMessages="false"
             logMessagesAtServiceLevel="true"
             logMessagesAtTransportLevel="false"
             maxMessagesToLog="3000"
             maxSizeOfMessageToLog="2000"/>
      </diagnostics>
    </system.serviceModel>
  <system.diagnostics>
    <sources>
      <source name="System.ServiceModel.MessageLogging">
        <listeners>
          <add name="messages"
          type="System.Diagnostics.XmlWriterTraceListener"
          initializeData="c:\temp\messages.svclog" />
        </listeners>
      </source>
    </sources>
  </system.diagnostics>

which in turns creates a file and in that file there is xml definition what is being sent.

<s:Body>
 <NewValue xmlns="http://tempuri.org/">
 <name xmlns:d4p1="http://schemas.datacontract.org/2004/07/WcfService1" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
 <d4p1:SecondValue><d4p1:Svalue1>200</d4p1:Svalue1><d4p1:Svalue2>100</d4p1:Svalue2></d4p1:SecondValue>
 </name>
 </NewValue></s:Body>
</xml>

and within PHP you are able to copy this. but note that the parameter to send is “name” which is not the same as the parameter above (namesec) you have to send to “name” which is what the soap end point is looking for.

class SecondName {
    public $Svalue1;
    public $Svalue2;
}
 
class NewName {
    public $SecondValue;
 
    public function NewName($s1, $s2)
    {
        $this->SecondValue = new SecondName();
        $this->SecondValue->Svalue1 = $s1;
        $this->SecondValue->Svalue2 = $s2;
    }
}
 
$objN = new NewName(200,100);
 
//Create a SOAP client
$client = new SoapClient("http://192.168.0.3/Service1.svc?wsdl");
$retVal = $client->NewValue(array ("name" => $objN));
 
print_r($retVal->NewValueResult);

and the output is

Value : 300

Have attached a file of the project for the WFC webserver and also the php code.

PHP – Use

From a follow on from my previous post about namespace, when you want to use another name, shorter than the actual namespace of the namespace you are able to use “use”. Probably best to show in code

include "codingfriends.php";
 
use codingfriends as cf;
 
echo cf\sayHello()."<br/>";

the codingfriends.php file is

<?php
namespace codingfriends;
 
function sayHello()
{
    echo "Say hello from codingfriends.";    
}
 
function sayHelloFromSub()
{
    echo sub\sayHello();
}
?>

so that the “use” will alter the namespace of codingfriends to cf instead so that you are able to call codingfriends as cf, so when

echo cf\sayHello()."<br/>";

is called it will call the codingfriends\sayHello() function.