Before moving ahead I want to introduce basic concept
of Asynchronous Programming
Problem
Sometimes in our
web application we request for data from webserver and we have to wait for
response. So in this case our entire application is blocked and user have to
wait till response from webserver.
Solution
Asynchronous
Programming is introduced to overcome above problem.
Asynchrony is
essential for activities that are potentially blocking, such as when your
application accesses the web. Access to a web resource sometimes is slow or
delayed. If such an activity is blocked within a synchronous process, the
entire application must wait. In an asynchronous process, the application can
continue with other work that doesn't depend on the web resource until the
potentially blocking task finishes
Difference between synchronous/asynchronous
operations
a)
Synchronization
means two or more operations are running in a same context (thread) so that one
may block another
b)
Synchronization
means two or more operations happen sequentially.
c)
Asynchronous
means two or more operations are running in different contexts (thread) so that
they can run concurrently and do not block each other.
Synchronous operation (fig 1)
|
Asynchronous operation (fig 2)
|
 |
 |
Explanation
1) From fig 1
a. Each task occurs in sequence.
b. Here from fig, step3 have to wait to
complete step2
2)
From
fig2
a.
async and await keywords has been introduced
b.
async
and await are pair keywords. You cannot use them in a standalone manner.
c.
async
is marked on a method. This keyword is just an indicator saying that this
method will have the await keyword.
d.
The
await keyword marks the position from where the task should resume. So you will
always find this keyword in conjunction with Task.
Here Step3 will execute
without waiting for step2 to complete
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