cuda extern __shared__
cuda extern shared is a declaration in C++ that specifies the usage of shared memory in CUDA programs. The keyword "extern" is used to indicate that the shared memory is defined externally, typically in the global scope. The "shared" qualifier is used to specify that the variable or array should be allocated in the shared memory.
When using the cuda extern shared declaration, the following steps are typically involved:
Define the shared memory variable: The shared memory variable is typically declared in the global scope, outside of any function. It can be a single variable or an array, depending on the requirements of the program.
Allocate shared memory: To allocate shared memory, the size of the shared memory variable needs to be specified. This is usually done using the CUDA runtime function "cudaMallocShared()". The allocated shared memory can be accessed by all threads within a thread block.
Use shared memory in kernel function: The kernel function is the function that is executed on the GPU. To use the shared memory variable within the kernel function, it needs to be declared as a parameter of the function. This allows all threads within the thread block to access the shared memory.
Access shared memory within the kernel function: Once the shared memory variable is declared as a parameter of the kernel function, it can be accessed by all threads within the thread block. Each thread can read from or write to the shared memory location specified by the shared memory variable.
Free shared memory: After the kernel function has completed its execution, the shared memory needs to be freed to avoid memory leaks. This is typically done using the CUDA runtime function "cudaFreeShared()".
By using the cuda extern shared declaration, programmers can take advantage of shared memory to optimize memory access and improve performance in CUDA programs.