Race condition Example

Duration: 4 min

This video lesson is available to enrolled students.

Return to /learn/BPSC/operating-systems/process-synchronization/intro-critical-section/asset-race-condition-example after enrolling

Inside: a video lesson and guided study material.

Module outline

  1. About the Course: About the Course
  2. Section 1 | Language (Hindi): भाषा, लिपि, ध्वनि, वर्ण, अक्षर, स्वर, व्यंजन, मात्रा और संयुक्ताक्षर, वर्तनी, वर्ण-विन्यास, अनुस्वार, अनुनासिक, चंद्रबिंदु और ‘र’ के रूप, शब्द, पद और शब्द-भेद, संज्ञा और सर्वनाम, विशेषण और क्रिया, लिंग, वचन, पुरुष और कारक, काल, वाच्य, वाक्य और वाक्य-भेद, संधि, समास, विलोम शब्द, पर्यायवाची शब्द, सामान्य अशुद्धियाँ, अनेक शब्दों के लिए एक शब्द, मुहावरे और लोकोक्तियाँ, अपठित गद्यांश और अपठित पद्यांश, Multi-Topic Content (Cross-Concept Material), वर्णमाला
  3. Section 1 | Language (उर्दू भाषा — 22 प्रश्न (निश्चित)): Spelling & Diacritics, Grammar (اسم, فعل, صفت, ضمیر), Vocabulary, Idioms & Proverbs, Comprehension
  4. Section 1 | Language (বাংলা / बांग्ला भाषा — 22 प्रश्न (निश्चित)): Bangla Script and Sounds, Bangla Grammar and Usage, Bangla Word Formation and Vocabulary, Reading and Text Interpretation
  5. Section 1 | Language (English): Vocabulary, Noun, Subject Verb Agreement (Verb Noun Agreement), Adjectives, Tenses, Pronoun, Verb, Adverb, Preposition, Articles, Determiner, Conjunction, Modals, Active Passive Voice (Voice), Direct and Indirect Speech, Sentence Correction (Error Correction), Sentence Completion (Fill in the blanks), Sentence Construction, Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Cloze Test (Cloze Passage), Verbal Analogy (Word Based Analogy), Facts, Inference and Judgements
  6. Section 2 | Primary Maths & Reasoning: Ratio and Proportion (Ratios), Divisibility Rules, Mixture and Alligation, Permutation and Combination, Number System, HCF LCM, Sequence and Series (Series), Speed Time and Distance, Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Percentage, Average, Profit and Loss, Simple Interest and Compound Interest, Time and Work, Mensuration and Geometry, Age Problems, Arithmetic, Powers and Exponents (Surds and Indices), Algebra, Probability, Trigonometry, Syllogisms, Seating Arrangements, Blood Relations, Directions (Direction Test), Analytical Reasoning (Counting Figures Reasoning), Puzzle Solving (Puzzles), Calendar, Clock, Cubes & Dices, Venn Diagram, Data Arrangement, Inequality, Analogy, Ranking, Order and Sequence
  7. Section 2 | General Awareness (GK + Current Affairs): Polity, Physics, Biology, State Wise GK, Chemistry, History, Geography, Indian Economy, Environment, GK- Current Affairs, Static General Knowledge
  8. Section 3 | Computer System and Org. (CSO): Basics of COA, Floating Point Rep, Cache Memory Organization, Instr Formats & Modes, Programming the Basic Computer, Input Output Organisation, Register Transfer and Microoperations, Control Unit Design
  9. Section 3 | Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, SQL, File Organization & Indexing, Relational Algebra, Relational Calculus, Transaction Management, Concurrency Control
  10. Section 3 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Process Synchronization
  11. Section 3 | Computer Networks: 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, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics
  12. Section 3 | Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Minimum Spanning Trees, Shortest Path Algos
  13. Section 3 | Theory Of Computation & Compiler Design: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization
  14. Section 3 | Emerging Trends (AI, Societal Ethics & MS Office): Artificial Intelligence, Emerging Tech Trends, Society, Law & Ethics, MS Office Applications
  15. Section 3 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Maintenance and Configuration Management, Software Testing
  16. Section 3 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  17. Section 3 | OOPS, C++, JAVA, HTML: OOPS with C++, Java, HTML Basics, CSS
  18. Section 3 | Java: Java Fundamentals, Array, String, IO & References
  19. Section 3 | Python: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  20. Section 3 | Digital Electronics: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation
  21. Section 3 | Multimedia: Multimedia
  22. BPSC Previous Year Papers:
  23. BPSC Full Mock Tests:
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.

Loading lesson…