Race condition Example

Duration: 4 min

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Module outline

  1. About the Course: About the Course
  2. Paper-1 & 2 | Basic Numeracy: Ratio and Proportion (Ratios), Divisibility Rules, Mixture and Alligation, Permutation and Combination, Logarithm, Number System, HCF LCM, Sequence and Series (Series), Speed Time and Distance, Percentage, Average, Mensuration and Geometry, Age Problems, Arithmetic, Statistics, Probability, Profit and Loss, Simple Interest and Compound Interest, Partnership, Speed Mathematics and Basic Mathematics, Algebra, Powers and Exponents (Surds and Indices), Time and Work, Pipe and Cistern, RSSB Specific Videos - Basic Numeracy
  3. Paper-1 & 2 | Data Interpretation: Data Interpretation
  4. Paper-1 & 2 | General Mental Ability: Mental Ability, RSSB Specific Videos - Mental Ability
  5. Paper-1 & 2 | Logical Reasoning and Analytical Ability: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Data Sufficiency, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Syllogisms, Seating Arrangements, Blood Relations, Directions (Direction Test), Analytical Reasoning (Counting Figures Reasoning), Puzzle Solving (Puzzles), Calendar, Clock, Cubes & Dices, Venn Diagram, Analogy, Ranking, Order and Sequence, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Data Arrangement, Logical Sequence Of Words, Crypt Arithmetic
  6. Paper-1 & 2 | Decision Making and Problem Solving: Selection Decision Table (Decision Making)
  7. Paper-1 | General Science: Physics, Biology, Chemistry, RSSB Specific Videos
  8. Paper-1 | General Awareness: State Wise GK, GK- Current Affairs
  9. Paper-2 | Fundamentals of Computer: Basics of COA, Number System, Floating Point Rep, Number Representation
  10. Paper - 2 | Digital Logic Systems: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits
  11. Paper-2 | Operating Systems: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Linux OS, Distributed Systems
  12. Paper-2 | Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, Relational Algebra, SQL, Relational Calculus, File Organization & Indexing, Transaction Management, Concurrency Control
  13. Paper-2 | Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing
  14. Paper-2 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  15. Paper 2 | Oops, C++, Java: Language Design, OOPS with C++, Java, .Net Programming, Java Fundamentals
  16. Paper 2 | Python: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  17. Paper 2 | Emerging Trends and AI: Emerging Tech Trends, Artificial Intelligence
  18. Paper-2 | Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Advanced Algorithms
  19. Paper 2 | Data Communication and Network Security: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Security, Ethical Hacking
  20. Paper-2 I Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  21. Paper-2 | Computer Organization and Architecture: Cache Memory Organization, Input Output Organisation, Instr Formats & Modes, Control Unit Design, Register Transfer and Microoperations
  22. Paper-2 | Web Development: JavaScript-Basics, HTML Basics, CSS, XML
  23. Pedagogy: Child Development, Concept of Pedagogy, Psychology, Theories, Inclusive Education, Experiential Pedagogy, Curriculum Framework & Reforms, National Education Policy (NEP) 2020
  24. Live Sessions: RSSB Live Sessions
  25. RSSB Paper 1 - Full Mock Tests:
  26. RSSB Paper 2 - Full Mock Tests:
  27. SCI Previous Year Papers:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This video solves a GATE-2015 operating-systems concurrency question. Two functions, P1 and P2, share a variable B with initial value 2. P1 executes C = B - 1; then B = 2 * C;, while P2 executes D = 2 * B; then B = D - 1;. The question asks for the number of distinct values that B can possibly take after execution. The instructor labels the four instructions I11, I12 for P1 and I21, I22 for P2. Because each function's two instructions must preserve their internal order, the possible interleavings are the six permutations of choosing which P1 instruction and which P2 instruction occur at each step. A table with Case 1 through Case 6 lists the six interleavings of I11, I12, I21, and I22. The instructor evaluates each case by tracking the shared variable B (and local variables C and D) through the sequence. For example, one interleaving gives I11: C = 2 - 1 = 1; then I21: D = 2 * 2 = 4; then I12: B = 2 * 1 = 2; then I22: B = 4 - 1 = 3. Other interleavings yield final values such as 2 and 3 (and in some orderings, other intermediate results). By circling the final B values across all six cases and removing duplicates, the instructor concludes that B can take 3 distinct final values. The answer '3' is circled at the bottom of the question slide.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The slide presents the GATE-2015 question in an orange-and-white two-column table labeled P1() and P2(). The top line states that the two functions share a variable B with an initial value of 2 and execute concurrently. P1 contains 'C = B - 1;' then 'B = 2 * C;'; P2 contains 'D = 2 * B;' then 'B = D - 1;'. The red bottom line asks for the number of distinct values B can possibly take after execution. Handwritten blue annotations progressively label the P1 steps as I1, J1 and the P2 steps as I2, J2 (later refined to I11, I12 and I21, I22), establishing the instruction labels used for interleaving analysis.

  2. 2:00 – 3:58 02:00-03:58

    The slide now shows two code blocks headed P1() and P2() with labeled instructions (I11) C = B - 1;, (I12) B = 2 * C; and (I21) D = 2 * B;, (I22) B = D - 1;. Below, a green-headed table lists six columns Case1 through Case6, each containing a vertical sequence of the four instruction labels in different orders. Blue vertical line marks highlight selected rows in Case1-Case4 as the instructor computes each interleaving. On-screen values such as C=1, D=4, B=2 appear during the step-by-step evaluation. The instructor circles key intermediate values (e.g., B=3) and crosses out redundant steps, then returns to the original question slide where the final answer '3' is circled at the bottom, indicating three distinct possible values for B.

The core teaching point is systematic enumeration of legal interleavings in a concurrent execution where each process's internal instruction order must be preserved. With two instructions per process, there are C(4,2) = 6 valid interleavings, which the instructor tabulates as Case1-Case6. The method is: (1) label each instruction, (2) list all order-preserving interleavings, (3) simulate the shared variable B through each sequence while tracking local variables C and D, (4) collect the final B values and count distinct ones. The worked example shows how one interleaving produces C=1, D=4, and a final B=3, while others produce different finals. The conclusion is that the number of distinct values B can take is 3, which is circled as the answer. This case-by-case table method is the key exam technique for GATE concurrency questions of this type.

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