7- Concurrency Issues

Jul 03, 2026 14:43 · 2:08 · English · Whisper Turbo · 4 वक्ता:
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S… Speaker 3 (7- Concurrency Issues)
In all the examples I've shown you so far,
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S… Speaker 3 (7- Concurrency Issues)
our download threads have been isolated from each other.
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S… Speaker 1 (7- Concurrency Issues)
But in a real world scenario,
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S… Speaker 3 (7- Concurrency Issues)
sometimes our threads may need to access and modify shared resources.
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S… Speaker 1 (7- Concurrency Issues)
For example,
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S… Speaker 3 (7- Concurrency Issues)
when downloading files,
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each thread may report the number of bytes it has downloaded to a shared object.
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S… Speaker 2 (7- Concurrency Issues)
With this object,
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S… Speaker 3 (7- Concurrency Issues)
we can keep track of the entire download progress and report it to the user.
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S… Speaker 3 (7- Concurrency Issues)
Now, if multiple threads access the same object and at least one
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S… Speaker 3 (7- Concurrency Issues)
of them changes this object,
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S… Speaker 3 (7- Concurrency Issues)
we're going to run into a couple of issues.
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S… Speaker 3 (7- Concurrency Issues)
The first issue happens when multiple threads try to modify
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S… Speaker 3 (7- Concurrency Issues)
the same data at the same time.
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S… Speaker 3 (7- Concurrency Issues)
It's like having one burger and three people wanting to eat it at the same time.
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S… Speaker 1 (7- Concurrency Issues)
It's not going to work.
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S… Speaker 3 (7- Concurrency Issues)
So if multiple threads try to change the same data,
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S… Speaker 3 (7- Concurrency Issues)
we may get wrong results or our application may crash.
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S… Speaker 2 (7- Concurrency Issues)
When this happens,
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S… Speaker 3 (7- Concurrency Issues)
we say we have a race condition,
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S… Speaker 3 (7- Concurrency Issues)
which means multiple threads are racing or competing to modify some
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S… Speaker 1 (7- Concurrency Issues)
data.
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S… Speaker 3 (7- Concurrency Issues)
I will show you an example of this in the next video.
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S… Speaker 3 (7- Concurrency Issues)
Another issue happens when one thread changes the shared data,
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S… Speaker 3 (7- Concurrency Issues)
but the changes are not visible to other threads.
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S… Speaker 3 (7- Concurrency Issues)
So different threads will have different views of the shared data.
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S… Speaker 3 (7- Concurrency Issues)
This is what we call a visibility problem.
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S… Speaker 3 (7- Concurrency Issues)
So if multiple threads access the same data and at least one of them tries to
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S… Speaker 3 (7- Concurrency Issues)
change it, we're going to have some problems.
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S… Speaker 1 (7- Concurrency Issues)
If they only want to read the shared data,
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S… Speaker 3 (7- Concurrency Issues)
that's perfectly fine.
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S… Speaker 4 (7- Concurrency Issues)
And by the way,
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S… Speaker 3 (7- Concurrency Issues)
these problems are not specific to Java.
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S… Speaker 3 (7- Concurrency Issues)
These are properties of concurrent systems.
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S… Speaker 3 (7- Concurrency Issues)
We have the same problem in databases because multiple users can modify the
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S… Speaker 3 (7- Concurrency Issues)
same data at the same time.
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S… Speaker 3 (7- Concurrency Issues)
I talked about this in my ultimate SQL course.
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S… Speaker 3 (7- Concurrency Issues)
So if you want to build a multi -threaded application,
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S… Speaker 3 (7- Concurrency Issues)
you need to have a proper understanding of these problems and know how to prevent
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S… Speaker 3 (7- Concurrency Issues)
them. You should write code that can be safely executed by many threads
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S… Speaker 1 (7- Concurrency Issues)
in parallel.
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S… Speaker 1 (7- Concurrency Issues)
This is what we call thread safe code.
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S… Speaker 3 (7- Concurrency Issues)
It's one of those terms that you see in the Java documentation a lot.
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S… Speaker 1 (7- Concurrency Issues)
Some classes are thread safe,
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S… Speaker 3 (7- Concurrency Issues)
which means they can be safely used across many parallel threads.
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S… Speaker 1 (7- Concurrency Issues)
We'll talk about this later.
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S… Speaker 1 (7- Concurrency Issues)
So in the next video,
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S… Speaker 3 (7- Concurrency Issues)
I'm going to show you concurrency problems in action.

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