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 memoryptr - 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 PetscDeviceContext
s 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
PetscDeviceContext
s for consecutive reads.
Operations using separate PetscDeviceContext
s 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 variablesPetscFoo->data
may not be).
See Also#
PetscDeviceArrayZero()
, PetscDeviceMalloc()
, PetscDeviceCalloc()
,
PetscDeviceFree()
Level#
intermediate
Location#
src/sys/objects/device/interface/memory.cxx
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