Consider the following code (with line numbers): ! typedef struct lock_t (int flag; ) lock_t; void init (lock_t mutex) ( 11 12 13 15 // 0-> lock is available, 1 -> held mutex->flag = 0; void lock (lock_t *mutex) ( while (mutex->flag == 1) // TEST the flag ; // spin-wait (do nothing) mutex->flag = 1; // now SET it! } void unlock (lock_t mutex) ( mutex->flag = 0; This code is defective in that it allows two threads to enter a critical section at the same time. Please give me a sequence of operations where this might occur.

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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I need help doing problem set questions regarding concurrency..................

Consider the following code (with line numbers):
1 typedef struct_lock_t (int flag; } lock_t;
2
4
6
7
30
11
15
void init (lock_t *mutex) {
}
// 0-> lock is available, 1 -> held
mutex->flag = 0;
void lock (lock_t *mutex) (
while (mutex->flag == 1) // TEST the flag
; // spin-wait (do nothing)
mutex-> flag = 1;
}
void unlock (lock_t *mutex) {
mutex->flag = 0;
// now SET it!
This code is defective in that it allows two threads to enter a critical
section at the same time. Please give me a sequence of operations
where this might occur.
Transcribed Image Text:Consider the following code (with line numbers): 1 typedef struct_lock_t (int flag; } lock_t; 2 4 6 7 30 11 15 void init (lock_t *mutex) { } // 0-> lock is available, 1 -> held mutex->flag = 0; void lock (lock_t *mutex) ( while (mutex->flag == 1) // TEST the flag ; // spin-wait (do nothing) mutex-> flag = 1; } void unlock (lock_t *mutex) { mutex->flag = 0; // now SET it! This code is defective in that it allows two threads to enter a critical section at the same time. Please give me a sequence of operations where this might occur.
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