Questions tagged [mutex]
19 questions
27
votes
5 answers
Is "releases mutexes in reverse order" required to make this deadlock-prevention method work?
Operating System Concepts says
7.4.4 Circular Wait
The fourth and final condition for deadlocks is the circular-wait condition. One
way to ensure that this condition never holds is to impose a total ordering of
all resource types and to require that…
Tim
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13
votes
2 answers
How to test and benchmark mutex implementations
As the title says: How do you properly test and benchmark different implementations of mutexes in c++?
Essentially I wrote my own std::mutex like class for a project running on a 2 core, armv7 with the aim to minimize the overhead in the uncontested…
MikeMB
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8
votes
5 answers
Implementing a hash table with true concurrency
This was recently a question I was asked in a screening and it got me thinking. I never totally settled on how the conversation ended, and I did some digging. None of the answers I saw seemed satisfactory to me.
The question is essentially "how…
kiss-o-matic
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8
votes
2 answers
Mutex vs Semaphore: How to implement them _not_ in terms of the other?
Recently I had to implement a Semaphore using a Mutex and a Conditional Variable (this combination is also known as a Monitor) for an exercise at the university:
the Semaphore's decrement operation blocks until its counter is more than zero before…
Qqwy
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6
votes
1 answer
Specify that a method needs a mutex held when calling
Current situation
Right now I have a method like
Data lookupData(Key id)
{
std::lock_guard lock(m_mutex);
auto it = m_dict.find(id);
if(it == m_dict.end())
{
return Data::Empty;
}
else
{
return…
Daniel McLaury
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4
votes
1 answer
Simple solution for calling a function only on one thread, queuing waiting calls?
Let’s assume there is a function EventHandler that is called on multiple threads at different points in time.
EventHandler has to call SomeOtherFunction, but these calls shall only happen on one thread at a time.
That means: If a call to…
Martin
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3
votes
2 answers
When should one utilize Atomic Operations?
I have never used atomic operations, and remain largely ignorant of how to utilize them. And yet, I often come across objects like this when peering into Qt's backend:
https://doc.qt.io/qt-6/qatomicinteger.html
This leads me to question if there is…
Anon
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3
votes
0 answers
Release Phase in Lamport's Mutual Exclusion Algorithm
I was studying Lamport's mutual exclusion algorithm from the original paper, and noticed a difference in the release phase to the one given in Wikipedia. In the original paper, author states that :
To release the resource, process Pi removes any…
Varun Hegde
- 181
- 3
2
votes
1 answer
Make multiple data structures thread safe without multiple mutexes
In my application, I have a class which I call a "Signal" (Think Qt signals if you are familiar with that) that represents a one-to-many connection. Objects can register handlers to the signal which, when "emitted" calls each of the handlers.
This…
Patrick Wright
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2
votes
0 answers
Testing an algorithm for safety in mutual exclusion
I am attempting to write a code to test Lamport's Mutual Exclusion algorithm for safety as a correctness measure. I am running the alogrithm on a single core cpu machine with multiple processes sharing the same processor clock. One of ways I was…
Varun Hegde
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1
vote
2 answers
design pattern to avoid deadlock with mutex in golang
What would the appropriate design pattern to avoid deadlock when several functions use the same mutex ?
It is quite easy to forget what method uses the lock and so it happens that you call a function that do a mutex.Lock() inside a function that…
cylon86
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- 3
1
vote
2 answers
Why is it that "the process that locks the mutex must be the one to unlock it "?
Here are some discussions about mutex (lock) and binary semaphore from two OS books.
Stalling's Operating Systems book says
A concept related to the binary semaphore is the mutex . A key difference
between the two is that the process that locks…
Tim
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1
vote
1 answer
Small Mutex Implementation?
The relatively large size of std::mutex on different platforms (e.g. 40 or even 80 bytes) is often explained as ensuring the mutexes don't occupy the same cache-lines and so don't incur logically unnecessary fetches and synchronization…
Persixty
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0
votes
1 answer
Difference between outcome of using mutex/spinlock/semaphore in this deadlock situation?
I'm not sure if my answers to the following exercise is correct:
Suppose the program is run with two threads. Further suppose that the
following sequence of events occurs:
Time Thread 0 Thread 1
0 …
Lilian Shi
- 11
0
votes
1 answer
Is a mutex lock always implemented as spin waiting?
Is a mutex lock always implemented as spin waiting?
Can a mutex lock be implemented as block waiting? (Operating System Concepts section 5.4 only mentions the implementation by spin waiting. See below.) (For comparison, a semaphore's waiting can be…
Tim
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