Readers-writers problem closed

Question

In Reader-writer problem, if a Writer is writing some data, can other reader reads the data at the same time?

If no, this is the code present in Galvin how does it taking care of above situation

Writer's process:

do {
wait(rw mutex);
. . .
/* writing is performed */
. . .
signal(rw mutex);
} while (true);

 

Reader's process:

do {
wait(mutex);
    read count++;
if (read count == 1)
    wait(rw mutex);
signal(mutex);
. . .
/* reading is performed */
. . .
wait(mutex);
    read count--;
if (read count == 0)
    signal(rw mutex);
signal(mutex);
} while (true);

Comments

No when writer is writing the data other reader can't read that same data, ME is satisfied in the given code as-Suppose that rw mutex is 1 initially then Writer process set it to 0 to enter CS.Meanwhile when reader tries to read the data locked by writer it has to wait till the signal(rw mutex) is performed by Writer.The reader waits in following code lines-

If(read count==1)

 wait(rw mutex)

As rw mutex is now 0 it cannot be reduce further thus reader waiting in loop until rw mutex is set back to 1.

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Yes agree when rw mutex will be issued by writer it will set it to 0 and when a reader will issue it it has to wait because value of rw mutex is already set to set to 0 and as he is the first reader and just got blocked it will block all other readers too.

Thank you Soumya!

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In the reader process the first section

Wait(muted)

---

Signal(muted)

This section ensures that at least one reader is reading and and in this section we make the semaphore rwmutex to 0 ensuring no writer can write when reading is being done

And

In the last sevtion

Waut(mutex)

----

Signal(mutex)

Ensures that no one is reading and it signal rw mutex allowing writer to write

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@Shivam Kasat my question was different I wanted to know whether reader is allowed to read during writing or not anyway thanks.