Assume a program has 10 threads and has no race conditions. It is running on a 4-core CPU (i.e. 4-threads can run simultaneously). The number of threads running in a critical section of this program would be

Question

BlackTom AI · Accepted Answer

A critical section permits only one thread at a time due to mutual exclusion, so the number of threads running in the critical section is 1.

1) Relevant concepts:
- Critical section: the portion of code that accesses shared resources and must not be concurrently executed by more than one thread.
- Mutual exclusion: synchronization mechanism (e.g., locks, mutexes, semaphores) that enforces only one thread enters the critical section at any moment.
- Race condition absence: indicates correct synchronization is in place, so the critical section is protected.

2) Step-by-step reasoning:
- The program has 10 threads total. That describes the number of threads that can potentially execute different parts of the program.
- The CPU has 4 cores, meaning up to 4 threads can execute simultaneously at the processor level.
- However, the absence of race conditions implies proper synchronization controls the critical section, enforcing mutual exclusion.
- Mutual exclusion guarantees that when one thread is executing the critical section, any other thread that reaches it must wait until the current thread leaves.

3) Intermediate “calculation” steps:
- Available threads: 10 (total)
- Simultaneously runnable threads due to cores: up to 4
- Allowed concurrent threads in critical section due to mutual exclusion: 1

4) Why the correct answer is correct:
Because mutual exclusion is the defining property of a critical section. Regardless of how many cores or threads exist, only one thread may be executing that protected code at any time if race conditions are prevented.

5) Why other plausible answers would be incorrect:
- Answer “4” (equal to number of cores) would be wrong because the number of cores limits concurrent execution generally but does not override mutual exclusion for a critical section.
- Answer “10” or any number >1 would be wrong because preventing race conditions means the critical section is serialized; multiple threads cannot be in it simultaneously.

6) Conclusion:
Therefore, the number of threads running in the critical section is 1, matching the provided correct answer.

Assume a program has 10 threads and has no race conditions. It is running on a 4-core CPU (i.e. 4-threads can run simultaneously). The number of threads running in a critical section of this program would be单项选择题

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