Can multiple threads read the same variable?

Even though the variable is not currently being written to, previous writes to the variable may not yet be visible to all threads. This means two threads can read the same value and get different results creating a race condition.

What is race condition in multi threading?

A race condition occurs when two threads access a shared variable at the same time. Then the first thread and second thread perform their operations on the value, and they race to see which thread can write the value last to the shared variable.

What will happen if multiple threads accessing the same resource?

Code that is safe to call by multiple threads simultaneously is called thread safe. If a piece of code is thread safe, then it contains no race conditions. Race condition only occur when multiple threads update shared resources.

What data have a race condition?

A race condition occurs when two or more threads can access shared data and they try to change it at the same time. Because the thread scheduling algorithm can swap between threads at any time, you don’t know the order in which the threads will attempt to access the shared data.

Is read only thread safe?

This ordering ensures that all instance fields are initialized by their variable initializers before any statements that have access to that instance are executed. For that reason, the value will be set before it is available to any thread, and will not change, so it is thread safe.

Do I need mutex for reading?

Unless you use a mutex or another form of memory barrier. So if you want correct behavior, you don’t need a mutex as such, and it’s no problem if another thread writes to the variable while you’re reading it.

What is the difference between race conditions and data races?

Race condition: A race condition is a situation, in which the result of an operation depends on the interleaving of certain individual operations. Data race: A data race is a situation, in which at least two threads access a shared variable at the same time.

Can multiple threads exist on one object?

As multiple threads exists on same object. Only one thread can hold object monitor at a time. As a result thread can notify other threads of same object that lock is available now.

What is shared and not shared between threads?

Threads share data and code while processes do not. The stack is not shared for both. Processes can also share memory, more precisely code, for example after a Fork() , but this is an implementation detail and (operating system) optimization.

What is the difference between race condition and data races are they the same?

How can race conditions be prevented?

Preventing Race Conditions Race conditions can be avoided by proper thread synchronization in critical sections. Thread synchronization can be achieved using a synchronized block of Java code. Thread synchronization can also be achieved using other synchronization constructs like locks or atomic variables like java.

Can multiple threads write to the same file at the same time?

Obviously using a read/write lock will defeat the purpose of having multiple threads, so the point is to have the threads writing at the same time in a non-serialized way. Second question: Is it even possible to open the same file in multiple threads and then safely having each thread write to a different part of it?

What happens when two threads write to the same atomic unit?

If two threads write more than an atomic unit (e.g., they both write a 128 bit value), then in fact the atomic unit sized pieces of the values written will be stored in a absolutely well defined way, but you won’t know which pieces of which value get written in what order.

Why is FILESTREAM not supported for multithreaded read/write?

The reason the FileStream is not supported for multithreaded read/write is spelled out in documentation (in short, file pointer is not synchronized across threads) From:  http://msdn.microsoft.com/en-us/library/system.io.filestream.aspx

Is it possible for a read thread to corrupt data?

At which point the read thread has stale data. The result is undefined. Corrupted data is entirely possible. For an obvious example, consider a 64-bit value being manipulated by a 32-bit processor. Let’s assume the value is a simple counter, and we increment it when the lower 32-bits contain 0xffffffff. The increment produces 0x00000000.