PetscDeviceMemset#

Memset device-aware memory

Synopsis#

#include <petscdevice.h> 
PetscErrorCode PetscDeviceMemset(PetscDeviceContext dctx, void *ptr, PetscInt v, std::size_t n)

Not Collective, Asynchronous, Auto-dependency aware

Input Parameters#

dctx - The PetscDeviceContext used to memset the memory
ptr - The pointer to the memory
v - The value to set
n - The amount (in bytes) to set

Notes#

ptr must have been allocated by PetscDeviceMalloc() or PetscDeviceCalloc().

The user should prefer PetscDeviceArrayZero() over this routine as it automatically computes the number of bytes to copy from the size of the pointer types, though they should note that it only zeros memory.

This routine is analogous to memset(). That is, this routine copies the value static_cast<unsigned char>(v) into each of the first count characters of the object pointed to by dest.

If dest is on device, this routine is asynchronous.

DAG representation#

  time ->

  -> dctx - |= CALL =| - dctx ->
  -> dest --------------------->

Asynchronous API Notes#

This routine is explicitly marked as exhibiting asynchronous behavior. Asynchronous behavior implies that routines launching operations on (or associated with) a PetscDeviceContext may return to the caller before the operation has completed.

Sequential Consistency:

Operations using the same PetscDeviceContext which access objects or memory regions are ordered per the language specification.

Operations using separate PetscDeviceContexts which access the same object or memory region are strongly write-ordered. That is, the following operations:

write-write
write-read
read-write

are strongly ordered. Formally:

Given an operation A-B (e.g. A = write, B = read) on an object or memory region M such that A “happens-before” B, where A uses PetscDeviceContext X and B uses PetscDeviceContext Y, then B shall not begin before A completes. This implies that any side-effects resulting from A are also observed by B.

Note the omission of read-read; there is no implied ordering between separate PetscDeviceContexts for consecutive reads.

Operations using separate PetscDeviceContexts which access separate objects or memory regions may execute in an arbitrary order and offer no guarantee of sequential consistency.

Memory Consistency:

If this routine modifies the participating object(s) then – unless otherwise stated – the contents of any externally held references to internal data structures should be considered to be in an undefined state. A well-defined state can only be restored by re-acquiring these references through the appropriate API or by calling PetscDeviceContextSynchronize().

Unless otherwise stated, exceptions to this rule are:

References returned by the routine itself. If a routine returns a pointer, the value of the top-most pointer is guaranteed to always be valid. For example, given a routine which asynchronously allocates memory and returns a pointer to the memory, the value of said pointer is immediately valid but dereferencing the pointer may not be.
References to structures. If a routine returns a PetscFoo, or array thereof then the objects themselves are always valid (though their member variables PetscFoo->data may not be).