Java Thread Synchronized
Name | Explanation and Usage |
---|---|
Resource Sharing | Multiple threads or processes need to access and use the same resources or data. In concurrent programming, it is essential to ensure the safe access to shared resources. |
Critical Section | A critical section is a block or region of code that accesses shared resources and needs to ensure that only one thread can enter. Locks or mutexes are often used to protect critical sections. |
Mutual Exclusion | Mutual exclusion is a synchronization mechanism used to ensure that only one thread can access shared resources at any given time. It is typically achieved using locks or mutexes. |
Locking/Mutex | A lock is a synchronization mechanism used to control the access of multiple threads to shared resources. Mutexes are often used to protect critical sections and prevent multiple threads from accessing them simultaneously. |
Semaphore | A semaphore is a synchronization mechanism used to control the concurrent access of multiple threads. It can be used to limit the number of threads accessing shared resources simultaneously. |
Monitor | A monitor is a high-level synchronization mechanism that includes locks and condition variables used to manage thread access to shared resources. It is typically provided by the programming language or library. |
Race Condition | A race condition occurs in a multithreaded environment when the program’s outcome depends on the order of thread execution rather than the code logic. Race conditions can lead to unpredictable results and errors. |
Inter-Thread Communication | Inter-thread communication refers to the process of passing information, sharing data, or collaborating on tasks between multiple threads. It typically requires synchronization mechanisms such as condition variables, semaphores, or queues. |
1. Resource Sharing
- Meaning: Multiple threads or processes need to access and use the same resources or data to ensure safe access to shared resources.
- Example Code: Multiple threads in a multithreaded program need to access a shared global counter.
1 | class SharedResource { |
In this example, two threads (thread1
and thread2
) share a SharedResource
instance and call the increment()
method to increase the value of count
. Since the increment()
method is synchronized, multiple threads cannot enter it simultaneously, ensuring the correct incrementing of count
. Finally, the final value of the shared resource is printed.
2. Critical Section
- Meaning: A critical section is a block or region of code that accesses shared resources and needs to ensure that only one thread can enter. Locks or mutexes are often used to protect critical sections.
- Example Code: In a multithreaded program, the code block accessing shared resources needs to be executed under the protection of a mutex.
1 | class SharedResource { |
In this example, the lock
object is used to create a synchronized block that ensures thread safety when accessing the count
variable in a multithreaded environment.
3. Mutual Exclusion
- Meaning: Mutual exclusion is a synchronization mechanism used to ensure that only one thread can access shared resources at any given time.
- Example Code: Using Java’s
synchronized
keyword to implement mutual exclusion.
1 | class SharedResource { |
In this example, the SharedResource
class contains a shared counter count
, and both the increment()
and getCount()
methods use the synchronized
keyword to ensure mutual exclusion. Two threads (thread1
and thread2
) operate on the SharedResource
simultaneously, but due to the mutual exclusion, they do not access the increment()
method at the same time, ensuring correct counting. Finally, the final value of the shared resource is printed.
4. Locking/Mutex
- Meaning: A lock is a synchronization mechanism used to control the access of multiple threads to shared resources.
- Example Code: Using Java’s
ReentrantLock
class to create locks.
1 | import java.util.concurrent.locks.ReentrantLock; |
This code uses ReentrantLock
to provide explicit locking and unlocking mechanisms, allowing more flexible control over the lock’s granularity and behavior compared to the synchronized
keyword.
5. Semaphore
- Meaning: A semaphore is a synchronization mechanism used to control the concurrent access of multiple threads.
- Example Code: Using Java’s
Semaphore
class to limit access to a resource.
1 | import java.util.concurrent.Semaphore; |
In this example, a semaphore with a single permit (value of 1) is used to ensure that only one thread accesses the shared resource at a time.
6. Monitor
- Meaning: A monitor is a high-level synchronization mechanism that includes locks and condition variables used to manage thread access to shared resources.
- Example Code: Java’s object monitors are composed of the
synchronized
keyword and thewait()
,notify()
,notifyAll()
methods.
1 | class SharedResource { |
This example uses the synchronized
keyword and wait-notify mechanism to implement thread synchronization and coordination. The wait()
and notifyAll()
methods allow threads to wait for specific conditions to be met and to notify other waiting threads when conditions are met.
7. Race Condition
- Meaning: A race condition occurs in a multithreaded environment when the program’s outcome depends on the order of thread execution rather than the code logic.
- Example Code: Multiple threads concurrently modifying shared resources without proper synchronization can lead to race conditions.
1 | class RaceConditionExample { |
To solve the race condition, use the synchronized
keyword to lock the shared resource, ensuring only one thread accesses the critical section at a time.
8. Inter-Thread Communication
- Meaning: Inter-thread communication refers to the process of passing information, sharing data, or collaborating on tasks between multiple threads.
- Example Code: Using Java’s
Lock
andCondition
interfaces to implement thread communication.
1 | import java.util.concurrent.locks.*; |
This example uses the Lock
and Condition
interfaces to achieve inter-thread communication, ensuring that threads coordinate access to shared resources and avoid race conditions and unpredictable results.