Skip to content

Latest commit

 

History

History
90 lines (64 loc) · 3.35 KB

9_Thread specificResourceSpecificCV.md

File metadata and controls

90 lines (64 loc) · 3.35 KB

Mutex and Condition Variable: Detailed Notes for Interview Preparation 📝🎥

Introduction 📚

The explains the concept of multiple condition variables in association with mutex and predicate. The discussion revolves around how many condition variables can be linked with a single mutex and how they behave in multithreading scenarios.

Key Concepts 💡

Condition Variable

  • It's associated with a mutex and a condition (or predicate).
  • It can be a property of either a resource or a thread.

Mutex (Mutual Exclusion)

  • Provides mutual exclusivity to a predicate.
  • It is always the property of a resource.

Predicate

  • A condition or a logical statement that threads check before proceeding.

Rules 📜

  • Multiple condition variables can associate with the same mutex.
  • A single condition variable cannot associate with multiple mutexes.

Scenario Explained 🎭

Threads and Resources

  • Imagine we have three threads: T1, T2, and T3.
  • Each thread has its own Condition Variable: CV1, CV2, and CV3.
  • There is a single resource R with its own mutex M.

Waiting and Blocking ⏳

  • If T1 finds the resource R is busy, it will wait (or block itself).
  • Thread T1 invokes pthread_cond_wait(), passing CV1 and Mutex M.

Signaling 🚦

  • A separate thread TS (Signaling Thread) can selectively signal any thread.
  • If TS wants to unblock T2, it will invoke pthread_cond_signal() with CV2.

Developer Control 🎮

  • Using thread-specific Condition Variables gives more control to the programmer.
  • Programmer can choose which thread to unblock.

Contrasting Scenarios 🔄

Resource-Specific Condition Variable

  • In this case, all threads share a single Condition Variable (CV).
  • The programmer loses control over which specific thread to unblock.
  • The operating system will decide which thread to unblock.

Summary 📝

  • Having separate condition variables gives the programmer finer control.
  • Sharing a condition variable across threads shifts control to the operating system.

Interview Questions and Answers 🤔💡

Q1: What is the role of a Mutex in the context of Condition Variables?

A: The role of the Mutex is to provide mutual exclusivity to the predicate that the Condition Variable checks. It ensures that when one thread is evaluating the predicate, no other thread can change its state.

Q2: Can a single Condition Variable be associated with multiple Mutexes?

A: No, a single Condition Variable cannot be associated with more than one Mutex at a time.

Q3: What is the advantage of having thread-specific Condition Variables?

A: Having thread-specific Condition Variables gives the programmer more control to selectively block or unblock specific threads.

Q4: In a scenario where multiple threads share a single Condition Variable, who decides which thread gets unblocked?

A: In such a scenario, the decision of which thread to unblock shifts from the programmer to the operating system. The OS will decide based on its scheduling policy.

Q5: Is the Mutex always the property of a resource?

A: Yes, Mutex is always the property of a resource, while a Condition Variable could be the property of a resource or a thread.

Feel free to review these notes and prepare well for your interviews! 🍀👍