The Cooperative Multitasking Environment
The cooperative multitasking environment is a standard part of system 7.0.
The Macintosh Operating System and the Finder work together to provide this
environment. MultiFinder is now transparent to the user; the user always has
the capability to run more than one application at a time. Because the user may
choose to run other applications in addition to your application, your
application needs to be capable of existing in a shared environment.
The Operating System schedules the processing of all applications and desk
accessories. When a user opens a document or application, the Operating
System loads the application code into memory and schedules the application to
run. The application runs at the next available opportunity. The next available
opportunity usually means when the current process or application gives up
the CPU. In most cases, the application runs immediately (or appears to the
user to run immediately).
Once an application is executing, the CPU is available only to that application.
The application can only be interrupted by hardware interrupts, and these are
transparent to the application. However, to allow the user to interact with
your application and others, you must periodically relinquish the CPU using
your application lets the user interact with your application and also with
other applications.
Although the user can have a number of open documents and applications, only
one application is the active application. The active application is the
application currently interacting with the user; its icon appears in the right
side of the menu bar. The active application displays its menu bar and is
responsible for highlighting the controls of its frontmost window.
When your application is the active application and the user switches to
another application (by clicking in the window of a document belonging to
another application, for example), the Operating System sends your
application a suspend event. When your application receives a suspend event,
it should prepare to suspend processing, allowing the user to switch to the
other application. For example, in response to a suspend event, your
application should remove the highlighting from the controls of its frontmost
window and take any other necessary actions. The suspension actually occurs
Your application also needs to be able to resume processing when the user
chooses to work with your application again. Your application receives a
resume event when the user switches back to your application. In response to a
resume event, your application should update the contents of its windows and
highlight the controls of its frontmost window.
The Operating System preserves the environment of your application when it
is suspended and re stores that environment before sending it a resume event.
Your application does not need to preserve or restore the operating
environment in response to suspend or resume events.
When you perform user testing of your application, you might want to
observe people using other applications as well as your application, to make
sure that your application works well in a cooperative environment.
information on how your application can handle suspend and resume events and
how your application can take advantage of the cooperative multitasking
environment.