Questions tagged [thread-safety]
A piece of code is thread-safe if it only manipulates data structures in a way that allows consistent execution of this code by multiple threads. A code may be thread safe, conditionally safe (mutual exclusion required) or unsafe (can only be safely used by one thread).
thread-safety
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Collection was modified; enumeration operation may not execute
I can't get to the bottom of this error, because when the debugger is attached, it does not seem to occur.
Collection was modified; enumeration operation may not execute
Below is the code.
This is a ...
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What is thread safe or non-thread safe in PHP?
I saw different binaries for PHP, like non-thread or thread safe?
What does this mean?
What is the difference between these packages?
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What does a lock statement do under the hood?
I see that for using objects which are not thread safe we wrap the code with a lock like this:
private static readonly Object obj = new Object();
lock (obj)
{
// thread unsafe code
}
So, what ...
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votes
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answers
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queue.Queue vs. collections.deque
I need a queue which multiple threads can put stuff into, and multiple threads may read from.
Python has at least two queue classes, queue.Queue and collections.deque, with the former seemingly using ...
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Why is Java's SimpleDateFormat not thread-safe? [duplicate]
Please tell with a code example why is SimpleDateFormat not threadsafe. What is the problem in this class?
Is The problem with format function of SimpleDateFormat?
Please give a code which ...
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votes
8
answers
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What exactly is a reentrant function?
Most of the times, the definition of reentrance is quoted from Wikipedia:
A computer program or routine is
described as reentrant if it can be
safely called again before its
previous invocation has ...
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votes
3
answers
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Use cases for RxJava schedulers
In RxJava there are 5 different schedulers to choose from:
immediate(): Creates and returns a Scheduler that executes work immediately on the current thread.
trampoline(): Creates and returns ...
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246
votes
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Is local static variable initialization thread-safe in C++11? [duplicate]
I know this is an often asked question, but as there are so many variants, I'd like to re-state it, and hopefully have an answer reflecting the current state. Something like
Logger& g_logger() {
...
- 5,171
230
votes
11
answers
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Java synchronized method lock on object, or method?
If I have 2 synchronized methods in the same class, but each accessing different variables, can 2 threads access those 2 methods at the same time? Does the lock occur on the object, or does it get as ...
- 12.4k
223
votes
9
answers
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Concurrent HashSet<T> in .NET Framework?
I have the following class.
class Test{
public HashSet<string> Data = new HashSet<string>();
}
I need to change the field "Data" from different threads, so I would like some opinions ...
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votes
5
answers
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C# Thread safe fast(est) counter
What is the way to obtain a thread safe counter in C# with best possible performance?
This is as simple as it gets:
public static long GetNextValue()
{
long result;
lock (LOCK)
{
...
- 4,850
208
votes
9
answers
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Automating the InvokeRequired code pattern
I have become painfully aware of just how often one needs to write the following code pattern in event-driven GUI code, where
private void DoGUISwitch() {
// cruisin for a bruisin' through ...
- 5,030
187
votes
15
answers
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views
Thread-safe List<T> property
I want an implementation of List<T> as a property which can be used thread-safely without any doubt.
Something like this:
private List<T> _list;
private List<T> MyT
{
get { // ...
- 30.6k
181
votes
4
answers
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views
What Makes a Method Thread-safe? What are the rules?
Are there overall rules/guidelines for what makes a method thread-safe? I understand that there are probably a million one-off situations, but what about in general? Is it this simple?
If a method ...
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173
votes
4
answers
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Are global variables thread-safe in Flask? How do I share data between requests?
In my application, the state of a common object is changed by making requests, and the response depends on the state.
class SomeObj():
def __init__(self, param):
self.param = param
def ...
- 2,251
171
votes
5
answers
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Is iterating ConcurrentHashMap values thread safe?
In javadoc for ConcurrentHashMap is the following:
Retrieval operations (including get) generally do not block, so may overlap with update operations (including put and remove). Retrievals reflect ...
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168
votes
4
answers
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Is it OK to use Gson instance as a static field in a model bean (reuse)?
Here's the model I implemented:
public class LoginSession {
private static final Gson gson = new Gson();
private String id;
private String name;
private long timestamp;
public ...
- 4,119
161
votes
12
answers
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views
What does threadsafe mean?
Recently I tried to Access a textbox from a thread (other than the UI thread) and an exception was thrown. It said something about the "code not being thread safe" and so I ended up writing a delegate ...
158
votes
3
answers
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views
Difference between -pthread and -lpthread while compiling
What is the difference between gcc -pthread and gcc -lpthread which is used while compiling multithreaded programs?
- 2,849
152
votes
3
answers
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To what degree does std::shared_ptr ensure thread-safety?
I'm reading http://gcc.gnu.org/onlinedocs/libstdc++/manual/shared_ptr.html and some thread safety issues are still not clear for me:
Standard guarantees that reference counting is handled thread safe ...
- 5,307
148
votes
10
answers
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views
How can I make a JUnit test wait?
I have a JUnit test that I want to wait for a period of time synchronously. My JUnit test looks like this:
@Test
public void testExipres(){
SomeCacheObject sco = new SomeCacheObject();
sco....
- 9,196
148
votes
5
answers
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views
Thread Safety in Python's dictionary
I have a class which holds a dictionary
class OrderBook:
orders = {'Restaurant1': None,
'Restaurant2': None,
'Restaurant3': None,
'Restaurant4': None}
...
- 7,571
145
votes
6
answers
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Are non-synchronised static methods thread safe if they don't modify static class variables?
I was wondering if you have a static method that is not synchronised, but does not modify any static variables is it thread-safe? What about if the method creates local variables inside it? For ...
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votes
8
answers
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Is the != check thread safe?
I know that compound operations such as i++ are not thread safe as they involve multiple operations.
But is checking the reference with itself a thread safe operation?
a != a //is this thread-safe
...
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129
votes
8
answers
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views
Is Random class thread safe?
Is it valid to share one instance of the Random class between multiple threads? And to call nextInt(int) from multiple threads in particular?
- 6,139
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votes
3
answers
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views
Does const mean thread-safe in C++11?
I hear that const means thread-safe in C++11. Is that true?
Does that mean const is now the equivalent of Java's synchronized?
Are they running out of keywords?
- 81.1k
120
votes
3
answers
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views
What do each memory_order mean?
I read a chapter and I didn't like it much. I'm still unclear what the differences is between each memory order. This is my current speculation which I understood after reading the much more simple ...
user34537
119
votes
7
answers
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views
Find if the installed PHP is threadsafe or nonthreadsafe?
How do I find out whether the installed version of PHP is threadsafe or not thread safe?
Please note that I'm not asking the difference between a threadsafe/non thread safe installation. I would like ...
- 1,337
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votes
3
answers
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Is SecureRandom thread safe?
Is SecureRandom thread safe? That is, after initializing it, can access to the next random number be relied on to be thread safe? Examining the source code seems to show that it is, and this bug ...
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110
votes
8
answers
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views
What's the best way of implementing a thread-safe Dictionary?
I was able to implement a thread-safe Dictionary in C# by deriving from IDictionary and defining a private SyncRoot object:
public class SafeDictionary<TKey, TValue>: IDictionary<TKey, ...
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votes
4
answers
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Threadsafe vs re-entrant
Recently, I asked a question, with title as "Is malloc thread safe?", and inside that I asked, "Is malloc re-entrant?"
I was under the impression that all re-entrant are thread-safe.
Is this ...
- 12.4k
107
votes
4
answers
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views
Is a HashMap thread-safe for different keys?
If I have two multiple threads accessing a HashMap, but guarantee that they'll never be accessing the same key at the same time, could that still lead to a race condition?
- 9,197
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votes
8
answers
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Why are local variables thread safe in Java
I was reading multi-threading in Java and I come across this
Local variables are thread safe in Java.
Since then I have been thinking How/Why local variables are thread safe.
Can somebody please ...
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votes
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answers
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views
How to ensure thread safety of utility static method?
Is there any general way or rules exits by which we can ensure the thread safety of static methods specifically used in various Utility classes of any applications. Here I want to specifically point ...
- 29.5k
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votes
3
answers
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how to know what is NOT thread-safe in ruby?
starting from Rails 4, everything would have to run in threaded environment by default. What this means is all of the code we write AND ALL the gems we use are required to be threadsafe
so, I have ...
- 33.9k
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votes
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Why is this class not thread safe?
class ThreadSafeClass extends Thread
{
private static int count = 0;
public synchronized static void increment()
{
count++;
}
public synchronized void decrement()
...
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votes
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answers
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Is it safe to call a synchronized method from another synchronized method?
If a synchronized method calls another synchronized method, is it thread safe?
void synchronized method1() {
method2()
}
void synchronized method2() {
}
- 21k
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iphone ios running in separate thread
What is the best way to run code on a separate thread? Is it:
[NSThread detachNewThreadSelector: @selector(doStuff) toTarget:self withObject:NULL];
Or:
NSOperationQueue *queue = [...
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votes
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answers
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Safety of Thread.current[] usage in rails
I keep getting conflicting opinions on the practice of storing information in the Thread.current hash (e.g., the current_user, the current subdomain, etc.). The technique has been proposed as a way to ...
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votes
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lock(new object()) -- Cargo cult or some crazy "language special case"?
I'm reviewing some code written by a consultant, and while dozens of red flags have already popped up, I can't wrap my head around the following snippet:
private void foo()
{
if (InvokeRequired)
...
user434817
87
votes
9
answers
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views
How do you implement a singleton efficiently and thread-safely? [duplicate]
The usual pattern for a singleton class is something like
static Foo &getInst()
{
static Foo *inst = NULL;
if(inst == NULL)
inst = new Foo(...);
return *inst;
}
However, it's my ...
- 5,559
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votes
14
answers
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views
Android - Best and safe way to stop thread
I want to know which is the best way to stop a thread in Android. I know I can use AsyncTask instead of it and that there is a cancel() method. I have to use Threads in my situation. Here is how I'm ...
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votes
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answers
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votes
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answers
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How to create a task (TPL) running a STA thread?
Using Thread is pretty straightforward
Thread thread = new Thread(MethodWhichRequiresSTA);
thread.SetApartmentState(ApartmentState.STA);
How to accomplish the same using Tasks in a WPF ...
- 2,506
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votes
4
answers
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views
Is RestTemplate thread safe?
Is a Spring RestTemplate thread-safe? That is
Is a RestTemplate a Strategy object that multiple connections can safely share. or
Is a RestTemplate a connection object (like a data-base connection), ...
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votes
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answers
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how to make an application thread safe?
I thought thread safe, in particular, means it must satisfy the need for multiple threads to access the same shared data. But, it seems this definition is not enough.
Can anyone please list out the ...
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votes
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What is "Linearizability"?
Can anyone out there help me understand what Linearizability is? I need an explanation that is simple and easy to understand. I'm reading The Art of Multiprocessor Programming by Maruice Herilihy ...
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What is the difference between SynchronizedCollection<T> and the other concurrent collections?
How does SynchronizedCollection<T> and the concurrent collections in the System.Collections.Concurrent namespace differ from each other, apart from Concurrent Collections being a namespace and ...
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votes
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Is java.sql.Connection thread safe?
To rephrase the question: should I avoid sharing instances of classes which implement java.sql.Connection between different threads?
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votes
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answers
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difference between standard's atomic bool and atomic flag
I wasn't aware of the std::atomic variables but was aware about the std::mutex (weird right!) provided by the standard; however one thing caught my eye: there are two seemingly-same (to me) atomic ...
- 3,014