Synchronization

Synchronization services (handling calls for the same services from different threads) are performed through the DKI thread. This thread is typically used for the shutdown and initialization of drivers, so it makes sense that synchronization services be handled within the DKI thread as well. The DKI thread is launched by the ChorusOS operating system microkernel at initialization time.

By ensuring this type of synchronization the DKI thread avoids using any other synchronization mechanism (locks) in the driver implementations.

The DKI thread acts as a synchronization mechanism in the following two cases:

Normal Case

In the normal case, all calls related to initialization/shutdown of the drivers are performed implicitly in the context of the DKI thread. This means that drivers need not be concerned with synchronization issues, because their routines are called directly from the DKI thread.

Special Cases

There are two special cases in which a driver must use DKI thread services to ensure synchronization:

• Hot-pluggable device drivers

  With a hot-pluggable device driver, the initialization/shutdown process must be executed at runtime (not as part of the kernel/drivers initialization process). In this case, drivers use DKI thread services (described below) to provide synchronization with any running drivers.

• Deferred driver initialization

  In some cases, a device driver may defer its initialization until it is opened. In this scheme, initialization/shutdown processes are executed at runtime (at time of open/close) and not as part of the kernel/driver's initialization process. Thus, this kind of driver uses thread services to synchronize with drivers that are already running.

  This is a way to resolve conflicts that arise when the same resources are used by multiple drivers. By using deferred driver initialization, drivers which share resources can be loaded at the same time (as long as they are not opened at the me time).

DKI thread related services are described below. See the man pages for complete descriptions of the commands listed:

svDkiThreadCall

synchronously invokes a routine in the context of the DKI thread.

svDkiThreadTrigger

asynchronously invokes a routine in the context of the DKI thread.