Locking allows different types of resources to be used exclusively by one process at a time.
For more information see Locks in Java
Questions tagged [locking]
8782 questions
49
votes
5 answers
synchronized block - lock more than one object
I'm modelling a game where multiple players (threads) move at the same time.
The information of where a player is located at the moment is stored twice: the player has a variable "hostField" that references to a field on the board and every field…
speendo
- 13,045
- 22
- 71
- 107
49
votes
2 answers
mutex.lock vs unique_lock
When should I prefer the first piece of code to the second, and do they have fundamental differences
std::mutex mtx;
mtx.lock();
... //protected stuff
mtx.unlock();
... //non-protected stuff
mtx.lock();
... //etc
and
std::mutex…
Morgan Fouque
- 643
- 1
- 7
- 17
49
votes
6 answers
C# How to detect an object is already locked
How can I detect whether an object is locked or not?
Monitor.TryEnter (as described in Is there a way to detect if an object is locked?) does not work for me because it locks the object if it is not locked.
I only want to check if it is locked and…
hwcverwe
- 5,287
- 7
- 35
- 63
49
votes
6 answers
Race conditions in django
Here is a simple example of a django view with a potential race condition:
# myapp/views.py
from django.contrib.auth.models import User
from my_libs import calculate_points
def add_points(request):
user = request.user
user.points +=…
Fragsworth
- 33,919
- 27
- 84
- 97
48
votes
2 answers
SQL atomic increment and locking strategies - is this safe?
I have a question about SQL and locking strategies. As an example, suppose I have a view counter for the images on my website. If I have a sproc or similar to perform the following statements:
START TRANSACTION;
UPDATE images SET counter=counter+1…
Alexander Torstling
- 18,552
- 7
- 62
- 74
48
votes
6 answers
Why is "lock (typeof (MyType))" a problem?
MSDN gives the following warning about the lock keyword in C#:
In general, avoid locking on a public
type, or instances beyond your code's
control. The common constructs lock
(this), lock (typeof (MyType)), and
lock ("myLock") violate…
Alex K
- 10,835
- 8
- 29
- 34
48
votes
4 answers
What is lock-free multithreaded programming?
I have seen people/articles/SO posts who say they have designed their own "lock-free" container for multithreaded usage. Assuming they haven't used a performance-hitting modulus trick (i.e. each thread can only insert based upon some modulo) how can…
user997112
- 29,025
- 43
- 182
- 361
48
votes
4 answers
How would you implement your own reader/writer lock in C++11?
I have a set of data structures I need to protect with a readers/writer lock. I am aware of boost::shared_lock, but I would like to have a custom implementation using std::mutex, std::condition_variable and/or std::atomic so that I can better…
jack
- 2,094
- 1
- 19
- 17
45
votes
3 answers
MySQL InnoDB: Difference Between `FOR UPDATE` and `LOCK IN SHARE MODE`
What is the exact difference between the two locking read clauses:
SELECT ... FOR UPDATE
and
SELECT ... LOCK IN SHARE MODE
And why would you need to use one over the other?
pje
- 21,801
- 10
- 54
- 70
44
votes
3 answers
Read Locks and Write Locks
I am a little unsure about read and write locks and just need someone to check if these facts about read/write locks are correct.
This is in reference to databases in general.
Read Locks:
Multiple read locks can be acquired by multiple threads at…
nknj
- 2,436
- 5
- 31
- 45
44
votes
1 answer
std::scoped_lock or std::unique_lock or std::lock_guard?
From this question I understand that std::scoped_lock is "a strictly superior version of std::lock_guard".
From this question I understand that "std::lock_guard and std::unique_lock are the same" except that std::unique_lock has some extra features…
lachy
- 1,833
- 3
- 18
- 27
44
votes
4 answers
Is it OK to use a string as a lock object?
I need to make a critical section in an area on the basis of a finite set of strings. I want the lock to be shared for the same string instance, (somewhat similar to String.Intern approach).
I am considering the following implementation:
public…
Zaid Masud
- 13,225
- 9
- 67
- 88
44
votes
5 answers
Do I need to lock or mark as volatile when accessing a simple boolean flag in C#?
Lets just say you have a simple operation that runs on a background thread. You want to provide a way to cancel this operation so you create a boolean flag that you set to true from the click event handler of a cancel button.
private bool…
Simon P Stevens
- 27,303
- 5
- 81
- 107
43
votes
10 answers
lock keyword in C#
I understand the main function of the lock key word from MSDN
lock Statement (C# Reference)
The lock keyword marks a statement
block as a critical section by
obtaining the mutual-exclusion lock
for a given object, executing a
statement, and…
David Basarab
- 72,212
- 42
- 129
- 156
43
votes
11 answers
Why is ConcurrentBag so slow in .Net (4.0)? Am I doing it wrong?
Before I started a project, I wrote a simple test to compare the performance of ConcurrentBag from (System.Collections.Concurrent) relative to locking & lists. I am extremely surprised that ConcurrentBag is over 10 times slower than locking with a…
Tachy
- 971
- 1
- 9
- 14