Can two threads access the same data at the same time?
A data race is a state, in which at least two threads access a shared data at the same time, and at least one of the threads is a writer. A critical section is a section of the code, which not more than one thread should access at any point in time.
Can two 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 happens when two threads have same priority?
Explanation: In cases where two or more thread with same priority are competing for CPU cycles, different operating system handle this situation differently. Explanation: Thread exist in several states, a thread can be running, suspended, blocked, terminated & ready to run.
How do you share variables between threads?
You should use volatile keyword to keep the variable updated among all threads. Using volatile is yet another way (like synchronized, atomic wrapper) of making class thread safe. Thread safe means that a method or class instance can be used by multiple threads at the same time without any problem.
How do threads share data with one another?
Threads are sometimes called lightweight processes because they have their own stack but can access shared data. Because threads share the same address space as the process and other threads within the process, the operational cost of communication between the threads is low, which is an advantage.
How do threads communicate with each other?
Inter-thread Communication All the threads in the same program share the same memory space. If an object is accessible to various threads then these threads share access to that object’s data member and thus communicate each other. The second way for threads to communicate is by using thread control methods.
Which thread will executed first if 2 threads have same priority?
When multiple threads are ready to execute, the JVM selects and executes the Runnable thread that has the highest priority. If this thread stops or becomes not runnable, the lower-priority threads will execute. In case two threads have the same priority, the JVM will execute them in FIFO order.
Which thread will be executed if both have same priority?
Whenever a thread yeilds control of the CPU another thread of the same priority is scheduled to run. A thread voluntarily yielding control of the CPU is called Cooperative Multitasking. JVM selects to run a Runnable thread with the highest priority. All Java threads have a priority in the range 1-10.
Do threads share same variables?
Tip: Unlike class and instance field variables, threads cannot share local variables and parameters. The reason: Local variables and parameters allocate on a thread’s method-call stack. As a result, each thread receives its own copy of those variables.
How do multiple threads update the same variable?
There are several options:
- Using no synchronization at all.
- Declaring the field as volatile.
- Using java.util.concurrent.AtomicLong, AtomicInteger etc.
- Protecting reads and writes with the same lock.
What is the relation between threads and stacks?
Threads share the code and data segments and the heap, but they don’t share the stack. There’s a difference between “able to access data in the stack” and sharing the stack. Those threads have their own stacks which get pushed and popped when they call methods.
What is multiple threading?
Multithreading is a model of program execution that allows for multiple threads to be created within a process, executing independently but concurrently sharing process resources. Depending on the hardware, threads can run fully parallel if they are distributed to their own CPU core.
How are two variables shared between two threads?
Two variables flag and val are shared between two threads Thread_A and Thread_B. Thread_A prints val=20 and then sets val to 30. Thread_B prints val=30, since val is modified in Thread_A. Thread_B then sets val to 20 which is again used in Thread_A. This demonstrates that variable val is shared between two threads.
How are condition variables used in multi-threaded programming?
A condition variable is a mechanism that allows threads to wait (without wasting CPU cycles) for some even to occur. Several threads may wait on a condition variable, until some other thread signals this condition variable (thus sending a notification).
What are some examples of multi threaded programming?
For instance, consider the case where two threads try to update two variables. One tries to set both to 0, and the other tries to set both to 1. If both threads would try to do that at the same time, we might get with a situation where one variable contains 1, and one contains 0.
What are the problems of running multiple threads?
One of the basic problems when running several threads that use the same memory space, is making sure they don’t “step on each other’s toes”. By this we refer to the problem of using a data structure from two different threads. For instance, consider the case where two threads try to update two variables.
