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# 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 `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 variables `PetscFoo->data` may not be).

## See Also

`PetscDeviceArrayZero()`, `PetscDeviceMalloc()`, `PetscDeviceCalloc()`, `PetscDeviceFree()`

## Level

intermediate

## Location

src/sys/objects/device/interface/memory.cxx

Index of all Device routines
Table of Contents for all manual pages
Index of all manual pages