What are Pointers? How to Use Them? and How they can Improve your C++ Programming Skills
Modern C++: Upgrade Your Skills with Shared Pointers!
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Is pointer assignment atomic in C++?
C++11 does know about threads, but once again doesn't say anything about the atomicity of assigning pointers. However C++11 does contain std::atomic<T*>, which is guaranteed to be atomic. Note that even if writing to a raw pointer is atomic on your platform the compiler is still free to move that assingment around, so that doesn't really buy ...
Is assigning a pointer in C program considered atomic on x86-64
My question is whether pointer assignment can be considered atomic on x86_64 architecture for a C program compiled with gcc m64 flag. OS is 64bit Linux and CPU is Intel (R) Xeon (R) CPU D-1548. One thread will be setting a pointer and another thread accessing the pointer. There is only one writer thread and one reader thread.
Guarantees about atomic pointer assignment
In C++03 there are no such guaranties, because the language in not aware of threads. However on Win32 pointer assignment is guaranteed to be atomic. Simple reads and writes to properly-aligned 32-bit variables are atomic operations. In other words, you will not end up with only one portion of the variable updated; all bits are updated in an ...
std::atomic<std::shared_ptr>
The partial template specialization of std::atomic for std:: shared_ptr < T > allows users to manipulate shared_ptr objects atomically.. If multiple threads of execution access the same std::shared_ptr object without synchronization and any of those accesses uses a non-const member function of shared_ptr then a data race will occur unless all such access is performed through an instance of std ...
std::atomic
Notes. There are non-member function template equivalents for all member functions of std::atomic.Those non-member functions may be additionally overloaded for types that are not specializations of std::atomic, but are able to guarantee atomicity.The only such type in the standard library is std:: shared_ptr < U >.. _Atomic is a keyword and used to provide atomic types in C.
Atomics
The atomic wrapper on a pointer T* std::atomic<T*> or on an integral type integ std::atomic<integ> enables the CAS (compare-and-swap) operations. ... The copy assignment operator for MyType must be trivial for all base classes of MyType and all non-static members of MyType. Only an automatic by the compiler-generated copy assignment operator is ...
Assignment operators
Assignment and compound assignment operators are binary operators that modify the variable to their left using the value to their right. Operator ... lhs is a (possibly qualified or atomic (since C11)) pointer and rhs is a null pointer constant such as NULL or a nullptr_t value (since C23) lhs has type (possibly qualified or atomic ...
C++
atomic specializations for integral (1) and pointer (2) types support compound assignments: Each of these functions accesses the contained value, apply the proper operator and return the value the contained value had immediately before the operation; all in a single atomic operation that cannot be affected by other threads. These functions behave as if the proper fetch_* member function was ...
Toward a Better Use of C11 Atomics
The ATOMIC_VAR_INIT () macro can be used to initialize atomic objects with static storage duration to a non-zero value, while the atomic_init () macro is used to initialize automatic or dynamically allocated objects. For example, the following statically initializes the global atomic variable index to -1: atomic_int index = ATOMIC_VAR_INIT (-1);
Interlocked Variable Access
The interlocked functions provide a simple mechanism for synchronizing access to a variable that is shared by multiple threads. They also perform operations on variables in an atomic manner. The threads of different processes can use these functions if the variable is in shared memory. The InterlockedIncrement and InterlockedDecrement functions ...
Is assigning a pointer atomic in go · Issue #38667
More generally, pointer assignment is atomic, but you need more than that to make an example like yours work. The Go project does not use the issue tracker for questions. Please use a forum for this discussion.
std::atomic<T>::operator=
pointer types only: atomic::fetch_max (C++26) atomic::fetch_min (C++26) ... Unlike most assignment operators, the assignment operators for atomic types do not return a reference to their left-hand arguments. They return a copy of the stored value instead. See also (constructor)
The atomic types (C++11)
Specializations and instantiations of the atomic template must have a deleted copy constructor, a deleted copy assignment operator, and a constexpr value constructor.. The standard library provides full specializations of the atomic template for integral types, one full specialization for the bool type, and partial specializations for all pointer types.
Atomic Pointers in Go 1.19
In Obj-C, atomic properties will ensure operations are performed one after another, to prevent threads from accessing a memory address at the same time. Since Go is multithreaded, it supports atomic operations as well. Go 1.19 introduces new atomic types. My favorite addition is atomic.Pointer , it provides a sleek alternative to atomic.Value .
Is assignment to C++ int and pointer variables atomic?
While int *could* be atomic on a given platform, it is certainly not required. Consider, for example, an implementation of C on a typical 8-bit CPU - all ints will have to be accessed with a pair of loads or stores. Pardon if this is the wrong newsgroup for this question, and/or if this question is naive.
std::atomic_...<std::shared_ptr>
7) Stores the shared pointer r in the shared pointer pointed to by p and returns the value formerly pointed-to by p, atomically. Equivalent to p->swap(r) and returns a copy of r after the swap. atomic_compare_exchange_weak_explicit (p, expected, desired, std::memory_order_seq_cst,std::memory_order_seq_cst).
atomic
Objects of atomic types contain a value of a particular type (T).The main characteristic of atomic objects is that access to this contained value from different threads cannot cause data races (i.e., doing that is well-defined behavior, with accesses properly sequenced).Generally, for all other objects, the possibility of causing a data race for accessing the same object concurrently qualifies ...
std::shared_ptr
std::shared_ptr is a smart pointer that retains shared ownership of an object through a pointer. Several shared_ptr objects may own the same object. The object is destroyed and its memory deallocated when either of the following happens: the last remaining shared_ptr owning the object is destroyed; ; the last remaining shared_ptr owning the object is assigned another pointer via operator= or ...
atomic package
The following example shows how to maintain a scalable frequently read, but infrequently updated data structure using copy-on-write idiom. package main import ( "sync" "sync/atomic" ) func main() { type Map map[string]string var m atomic.Value m.Store(make(Map)) var mu sync.Mutex // used only by writers // read function can be used to read the data without further synchronization read := func ...
reference assignment is atomic so why is Interlocked.Exchange(ref
Reference assignment is atomic. Interlocked.Exchange does not do only reference assignment. It does a read of the current value of a variable, stashes away the old value, and assigns the new value to the variable, all as an atomic operation. my colleague said that on some platforms it's not guaranteed that reference assignment is atomic.
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C++11 does know about threads, but once again doesn't say anything about the atomicity of assigning pointers. However C++11 does contain std::atomic<T*>, which is guaranteed to be atomic. Note that even if writing to a raw pointer is atomic on your platform the compiler is still free to move that assingment around, so that doesn't really buy ...
My question is whether pointer assignment can be considered atomic on x86_64 architecture for a C program compiled with gcc m64 flag. OS is 64bit Linux and CPU is Intel (R) Xeon (R) CPU D-1548. One thread will be setting a pointer and another thread accessing the pointer. There is only one writer thread and one reader thread.
In C++03 there are no such guaranties, because the language in not aware of threads. However on Win32 pointer assignment is guaranteed to be atomic. Simple reads and writes to properly-aligned 32-bit variables are atomic operations. In other words, you will not end up with only one portion of the variable updated; all bits are updated in an ...
The partial template specialization of std::atomic for std:: shared_ptr < T > allows users to manipulate shared_ptr objects atomically.. If multiple threads of execution access the same std::shared_ptr object without synchronization and any of those accesses uses a non-const member function of shared_ptr then a data race will occur unless all such access is performed through an instance of std ...
Notes. There are non-member function template equivalents for all member functions of std::atomic.Those non-member functions may be additionally overloaded for types that are not specializations of std::atomic, but are able to guarantee atomicity.The only such type in the standard library is std:: shared_ptr < U >.. _Atomic is a keyword and used to provide atomic types in C.
The atomic wrapper on a pointer T* std::atomic<T*> or on an integral type integ std::atomic<integ> enables the CAS (compare-and-swap) operations. ... The copy assignment operator for MyType must be trivial for all base classes of MyType and all non-static members of MyType. Only an automatic by the compiler-generated copy assignment operator is ...
Assignment and compound assignment operators are binary operators that modify the variable to their left using the value to their right. Operator ... lhs is a (possibly qualified or atomic (since C11)) pointer and rhs is a null pointer constant such as NULL or a nullptr_t value (since C23) lhs has type (possibly qualified or atomic ...
atomic specializations for integral (1) and pointer (2) types support compound assignments: Each of these functions accesses the contained value, apply the proper operator and return the value the contained value had immediately before the operation; all in a single atomic operation that cannot be affected by other threads. These functions behave as if the proper fetch_* member function was ...
The ATOMIC_VAR_INIT () macro can be used to initialize atomic objects with static storage duration to a non-zero value, while the atomic_init () macro is used to initialize automatic or dynamically allocated objects. For example, the following statically initializes the global atomic variable index to -1: atomic_int index = ATOMIC_VAR_INIT (-1);
The interlocked functions provide a simple mechanism for synchronizing access to a variable that is shared by multiple threads. They also perform operations on variables in an atomic manner. The threads of different processes can use these functions if the variable is in shared memory. The InterlockedIncrement and InterlockedDecrement functions ...
More generally, pointer assignment is atomic, but you need more than that to make an example like yours work. The Go project does not use the issue tracker for questions. Please use a forum for this discussion.
pointer types only: atomic::fetch_max (C++26) atomic::fetch_min (C++26) ... Unlike most assignment operators, the assignment operators for atomic types do not return a reference to their left-hand arguments. They return a copy of the stored value instead. See also (constructor)
Specializations and instantiations of the atomic template must have a deleted copy constructor, a deleted copy assignment operator, and a constexpr value constructor.. The standard library provides full specializations of the atomic template for integral types, one full specialization for the bool type, and partial specializations for all pointer types.
In Obj-C, atomic properties will ensure operations are performed one after another, to prevent threads from accessing a memory address at the same time. Since Go is multithreaded, it supports atomic operations as well. Go 1.19 introduces new atomic types. My favorite addition is atomic.Pointer , it provides a sleek alternative to atomic.Value .
While int *could* be atomic on a given platform, it is certainly not required. Consider, for example, an implementation of C on a typical 8-bit CPU - all ints will have to be accessed with a pair of loads or stores. Pardon if this is the wrong newsgroup for this question, and/or if this question is naive.
7) Stores the shared pointer r in the shared pointer pointed to by p and returns the value formerly pointed-to by p, atomically. Equivalent to p->swap(r) and returns a copy of r after the swap. atomic_compare_exchange_weak_explicit (p, expected, desired, std::memory_order_seq_cst,std::memory_order_seq_cst).
Objects of atomic types contain a value of a particular type (T).The main characteristic of atomic objects is that access to this contained value from different threads cannot cause data races (i.e., doing that is well-defined behavior, with accesses properly sequenced).Generally, for all other objects, the possibility of causing a data race for accessing the same object concurrently qualifies ...
std::shared_ptr is a smart pointer that retains shared ownership of an object through a pointer. Several shared_ptr objects may own the same object. The object is destroyed and its memory deallocated when either of the following happens: the last remaining shared_ptr owning the object is destroyed; ; the last remaining shared_ptr owning the object is assigned another pointer via operator= or ...
The following example shows how to maintain a scalable frequently read, but infrequently updated data structure using copy-on-write idiom. package main import ( "sync" "sync/atomic" ) func main() { type Map map[string]string var m atomic.Value m.Store(make(Map)) var mu sync.Mutex // used only by writers // read function can be used to read the data without further synchronization read := func ...
Reference assignment is atomic. Interlocked.Exchange does not do only reference assignment. It does a read of the current value of a variable, stashes away the old value, and assigns the new value to the variable, all as an atomic operation. my colleague said that on some platforms it's not guaranteed that reference assignment is atomic.