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D.10 Synchronous Task Control
This clause describes a language-defined private
semaphore (suspension object), which can be used for two-stage suspend
operations and as a simple building block for implementing higher-level
The following language-defined
package Ada.Synchronous_Task_Control is
type Suspension_Object is limited private;
procedure Set_True(S : in out Suspension_Object);
procedure Set_False(S : in out Suspension_Object);
function Current_State(S : Suspension_Object) return Boolean;
procedure Suspend_Until_True(S : in out Suspension_Object);
... -- not specified by the language
The type Suspension_Object is a by-reference type.
An object of the type Suspension_Object has two
visible states: true and false. Upon initialization, its value is set
The operations Set_True and Set_False are atomic
with respect to each other and with respect to Suspend_Until_True; they
set the state to true and false respectively.
Current_State returns the current state of the
The procedure Suspend_Until_True blocks the calling
task until the state of the object S is true; at that point the task
becomes ready and the state of the object becomes false.
is raised upon calling Suspend_Until_True if another task is already
waiting on that suspension object. Suspend_Until_True is a potentially
blocking operation (see 9.5.1
The implementation is required to allow the calling
of Set_False and Set_True during any protected action, even one that
has its ceiling priority in the Interrupt_Priority range.
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