HP SVA V2.0 Parallel Compositing Reference Guide

Table 2-6 Context Functions (continued)
DescriptionFunction
Retrieves a context property as an integer.
pcContextGetInteger
Retrieves a context property as a string.
pcContextGetString
Sets an integer context property.
pcContextSetInteger
Sets a string context property.
pcContextSetString
Synchronizes context changes for all hosts.
pcContextSync
Parallel compositing is based on the concept of multiple processes or threads creating parts of
an image that are then combined and displayed. The Library identifies each of these processes
or threads as a host. To coordinate their work, the hosts share a context. Each host creates the
context using a “context create” function. The hosts can share information and coordinate their
execution through the context.
One of the hosts is the master and the remaining hosts are called slaves. From a Library point of
view, the distinction between the master and the slaves is slight.
All hosts have access to the full API with one exception. The master creates the context by calling
pcContextCreateMaster. This function specifies all the hosts that will be members of the
context. The slaves create the context by calling pcContextCreate.
A host is identified by a tuple:
hostName:hostId
hostName
Name of the system that runs the host.
hostId
An integer used to distinguish two hosts running on the same system.
This tuple is represented frequently as a string with a colon separating the two parts. For example:
red4:2 (system red4, hostId 2)
n1.cei.com:0 (system n1.cei.com, hostId 0)
Each host that is a member of a context must have a unique hostName:hostId tuple. However,
two hosts in different contexts having the same hostName:hostId pair are unrelated from the
point of view of the Library. The Library must be able to create a network connection to a machine
using the hostName. How this works can vary based on the network in use.
2.5 Context Properties
A Library session can contain one or more contexts. A context is a shared space among the hosts
that are members of the context. Each of the hosts can set and retrieve properties of the context.
Table 2-7 and Table 2-8 characterize context properties based on various characteristics. Use the
two tables in combination to understand how context properties differ.
As described in Table 2-7, a property's value is either global or host-specific. Global properties
have a single value that is the same for all hosts in the context. A host-specific property can have
a different value for each host.
Some properties cannot be set when the context is created. The Can Set On Context Create column
in the two tables provides this information.
Some properties cannot change (read-only) once the context is created. The Can Change After
Context Create column in the two tables provides this information.
Table 2-8 provides some examples of how the characteristics of the properties can affect their
behavior. Note that only the master can specify properties when creating a context.
30 Overview of Functions and Properties