PetscDeviceContextWaitForContext#

Make one context wait for another context to finish

Synopsis#

#include <petscdevice.h> 
PetscErrorCode PetscDeviceContextWaitForContext(PetscDeviceContext dctxa, PetscDeviceContext dctxb)

Not Collective

Input Parameters#

dctxa - The PetscDeviceContext object that is waiting
dctxb - The PetscDeviceContext object that is being waited on

Notes#

Serializes two PetscDeviceContexts. Serialization is performed asynchronously; the host does not wait for the serialization to actually occur.

This routine uses only the state of dctxb at the moment this routine was called, so any future work queued will not affect dctxa. It is safe to pass the same context to both arguments (in which case this routine does nothing).

DAG representation#

  time ->

  -> dctxa ---/- |= CALL =| - dctxa ->
             /
  -> dctxb -/------------------------>

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).