Table of Contents
- 1 Why static variables are not thread safe?
- 2 Are static variables thread safe in C?
- 3 Are static local variables shared between threads?
- 4 How do I make a static variable thread safe in C++?
- 5 What is local static variable in C?
- 6 What would happen if we declared a local variable as static local?
- 7 Is it thread safe to use a local static variable?
- 8 Is static initialization in C++11 thread safe?
Why static variables are not thread safe?
Static variables are not thread safe. Instance variables do not require thread synchronization unless shared among threads. But, static variables are always shared by all the threads in the process. Hence, access to static variable is not thread safe.
Are static variables thread safe in C?
In C, local static variables are initialized in a thread-safe manner because they’re always initialized at program startup, before any threads can be created. It is not allowed to initialize local static variables with non-constant values for precisely that reason.
Is local static thread safe?
The implementation must not introduce any deadlock around execution of the initializer. So yes, you’re safe.
Why static local variables are not allowed?
In Java, a static variable is a class variable (for whole class). So if we have static local variable (a variable with scope limited to function), it violates the purpose of static. Hence compiler does not allow static local variable.
Static variables are indeed shared between threads, but the changes made in one thread may not be visible to another thread immediately, making it seem like there are two copies of the variable.
How do I make a static variable thread safe in C++?
There are three ways in C++ to initialize variables in a thread safe way.
- Constant expressions.
- The function std::call_once in combination with the flag std::once_flag.
- Static variables with block scope.
Is static global variable thread safe?
According to following resources, in C++(Specially Visual C++) scoped static variable initialization isn’t thread safe. But, global static variables are safe.
Is static variable initialization thread safe?
The rule for static variables at block scope (as opposed to static variables with global scope) is that they are initialized the first time execution reaches their declaration. …
What is local static variable in C?
A local static variable is a variable, whose lifetime doesn’t stop with a function call where it is declared. It extends until the lifetime of a complete program. These variables are used to count the number of times a function is called. The default value of static variable is 0.
What would happen if we declared a local variable as static local?
When applied to a local variable, the static keyword defines the local variable as having static duration, meaning the variable will only be created once, and will not be destroyed until the end of the program.
How are local variables thread safe?
Local variables are stored in each thread’s own stack. That means that local variables are never shared between threads. That also means that all local primitive variables are thread safe.
Why are local variables thread safe in Java?
On its stack(basically thread stack), local primitives and local reference variables are stored. Hence one thread does not share its local variables with any other thread as these local variables and references are inside the thread’s private stack. Hence local variables are always thread-safe.
Is it thread safe to use a local static variable?
Using a local static variable makes the program not thread-safe in the same way that a global variable (when not protected by locks) is not thread-safe. You can think of local static variables as “global” in the sense of the program’s memory space, but with limited access enforced by the programming language at the scope in which it is defined.
Is static initialization in C++11 thread safe?
Starting in C++11, scoped static initialization is now thread-safe, but it comes with a cost: Reentrancy now invokes undefined behavior.] The rule for static variables at block scope (as opposed to static variables with global scope) is that they are initialized the first time execution reaches their declaration.
Is –FNO-threadsafe-statics safe to use?
So yes, you’re safe. (This says nothing of course about the subsequent access to the variable through the reference.) –fno-threadsafe-statics also worth mentioning. In gcc: Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics.
When should static variables be initialized in C++?
Starting in C++11, scoped static initialization is now thread-safe, but it comes with a cost: Reentrancy now invokes undefined behavior.] The rule for static variables at block scope (as opposed to static variables with global scope) is that they are initialized the first time execution reaches their declaration.