Class RCriticalSection

RCriticalSection

Support

Supported from 5.0

Description

A handle to a critical section.

A critical section itself is a Kernel object, and is implemented using a semaphore. The class RCriticalSection inherits privately from RSemaphore as a matter of implementation and this is, in effect, equivalent to using a semaphore.

The public functions of RSemaphore are not part of the public API of this class.

As with all handles, they should be closed after use. This class provides the necessary Close() function, which should be called when the handle is no longer required.

Derivation

RCriticalSection A handle to a critical section RHandleBase A handle to an object RSemaphore A handle to a semaphore

Defined in RCriticalSection:
Close(), CreateLocal(), IsBlocked(), RCriticalSection(), Signal(), Wait()

Inherited from RHandleBase:
Duplicate(), Handle(), SetHandle()

Inherited from RSemaphore:
Count(), CreateGlobal(), Open(), OpenGlobal()

See also:

• RHandleBase::Close()

RCriticalSection();

Description

Constructs the object.

The constructor exists to initialise private data within this handle; it does not create the critical section object.

TInt CreateLocal(TOwnerType aType=EOwnerProcess);

Description

Creates a critical section and opens this handle to the critical section.

The Kernel side object representing the critical section is unnamed. This means that it is not possible to search for the critical section, which makes it local to the current process.

By default, any thread in the process can use this instance of RCriticalSection to access the critical section. However, specifying EOwnerThread as the parameter to this function, means that only the creating thread can use this instance of RCriticalSection to access the critical section; any other thread in this process that wants to access the critical section must duplicate this handle.

Parameters

TOwnerType aType An enumeration whose enumerators define the ownership of this critical section handle. If not explicitly specified, EOwnerProcess is taken as default.

Return value

TInt KErrNone if successful otherwise another of the system wide error codes.

See also:

• RHandleBase::Duplicate()

void Close();

Description

Closes the handle to the critical section object.

As a critical section object is implemented using a semaphore, this has the effect of closing the handle to the semaphore.

void Wait();

Description

Waits for access to the critical section.

If no other thread is in the critical section, control returns immediately and the current thread can continue into the section.

If another thread is already in the critical section, the current thread is marked as waiting (on a semaphore); the current thread is added to the end of a FIFO queue of threads maintained by this critical section.

void Signal();

Description

Signals an exit from the critical section.

A thread calls Signal() when it exits from the critical section. The first thread waiting on the critical section’s queue of threads is removed from that queue and, provided that it is not suspended for any other reason, is marked as ready to run. That thread will, therefore, be the next to proceed into the critical section.

TBool IsBlocked() const;

Description

Tests whether the critical section is occupied by another thread.

Return value

TBool True, if the critical section is occupied by another thread. False, otherwise.