L4::Semaphore Struct Reference

C++ Kernel-provided semaphore interface, see Kernel-provided semaphore for the C interface. More...

#include <semaphore>

Inheritance diagram for L4::Semaphore:

Collaboration diagram for L4::Semaphore:

Public Member Functions
l4_msgtag_t	up (l4_utcb_t *utcb=l4_utcb()) noexcept
	Semaphore up operation (wrapper for trigger()).
l4_msgtag_t	down (l4_timeout_t timeout=L4_IPC_NEVER, l4_utcb_t *utcb=l4_utcb()) noexcept
	Semaphore down operation.
Public Member Functions inherited from L4::Triggerable
l4_msgtag_t	trigger (l4_utcb_t *utcb=l4_utcb()) noexcept
	Trigger the object.
Public Member Functions inherited from L4::Irq_eoi
l4_msgtag_t	unmask (unsigned irqnum, l4_umword_t *label=0, l4_timeout_t to=L4_IPC_NEVER, l4_utcb_t *utcb=l4_utcb()) noexcept
	Unmask the given interrupt line.

Additional Inherited Members
Protected Types inherited from L4::Kobject_t< Semaphore, Triggerable, L4_PROTO_SEMAPHORE >
typedef Semaphore	Class
	The target interface type (inheriting from Kobject_t)
typedef Typeid::Iface< PROTO, Semaphore >	__Iface
	The interface description for the derived class.
typedef Typeid::Merge_list< Typeid::Iface_list< __Iface >, typename Base::__Iface_list >	__Iface_list
	The list of all RPC interfaces provided directly or through inheritance.
Protected Types inherited from L4::Kobject_t< Triggerable, Irq_eoi, L4_PROTO_IRQ >
typedef Triggerable	Class
	The target interface type (inheriting from Kobject_t)
typedef Typeid::Iface< PROTO, Triggerable >	__Iface
	The interface description for the derived class.
typedef Typeid::Merge_list< Typeid::Iface_list< __Iface >, typename Base::__Iface_list >	__Iface_list
	The list of all RPC interfaces provided directly or through inheritance.
Protected Member Functions inherited from L4::Kobject_t< Semaphore, Triggerable, L4_PROTO_SEMAPHORE >
L4::Cap< Class >	c () const noexcept
	Get the capability to ourselves.
Protected Member Functions inherited from L4::Kobject_t< Triggerable, Irq_eoi, L4_PROTO_IRQ >
L4::Cap< Class >	c () const noexcept
	Get the capability to ourselves.
Static Protected Member Functions inherited from L4::Kobject_t< Semaphore, Triggerable, L4_PROTO_SEMAPHORE >
static void	__check_protocols__ () noexcept
	Helper to check for protocol conflicts.
Static Protected Member Functions inherited from L4::Kobject_t< Triggerable, Irq_eoi, L4_PROTO_IRQ >
static void	__check_protocols__ () noexcept
	Helper to check for protocol conflicts.

Detailed Description

C++ Kernel-provided semaphore interface, see Kernel-provided semaphore for the C interface.

This is the interface for kernel-provided semaphore objects. The object provides the classical functions up() and down() for counting the semaphore and blocking. The semaphore is a Triggerable with respect to the up() function, this means that a semaphore can be bound to an interrupt line at an ICU (L4::Icu) and incoming interrupts increment the semaphore counter.

The down() method decrements the semaphore counter and blocks if the counter is already zero. Blocking on a semaphore may—as all blocking operations—either return successfully, or be aborted due to an expired timeout provided to the down() operation, or due to an L4::Thread::ex_regs() operation with the L4_THREAD_EX_REGS_CANCEL flag set.

The main reason for using a semaphore instead of an L4::Irq is to ensure that incoming trigger signals do not interfere with any open-wait operations, as used for example in a server loop.

Definition at line 52 of file semaphore.

Member Function Documentation

down()

l4_msgtag_t L4::Semaphore::down ( l4_timeout_t  timeout = L4_IPC_NEVER, l4_utcb_t *  utcb = l4_utcb()  )

inlinenoexcept

Semaphore down operation.

Parameters

timeout	Timeout for blocking the semaphore down operation. Note: The receive timeout of this timeout-pair is significant for blocking, the send part is usually non-blocking.
utcb	UTCB to be used for this operation, shall be the UTCB of the calling thread. See l4_utcb.

Returns

Syscall return tag. Use l4_error() to check for errors.

Return values

-L4_EPERM

No L4_CAP_FPAGE_S right on invoked semaphore capability.

This method decrements the semaphore counter by one, or blocks if the counter is already zero, until either a timeout or cancel condition hits or the counter is increased by an up() operation.

Definition at line 88 of file semaphore.

up()

l4_msgtag_t L4::Semaphore::up ( l4_utcb_t *  utcb = l4_utcb() )

inlinenoexcept

Semaphore up operation (wrapper for trigger()).

Parameters

utcb	UTCB to be used for this operation, shall be the UTCB of the calling thread. See l4_utcb.

Returns

Syscall return tag for a send-only operation, this means there is no return value except L4_MSGTAG_ERROR indicating success or failure of the send operation. Use l4_ipc_error() to check for errors and do not use l4_error().

Increases the semaphore counter by one if it is smaller than an unspecified limit. The unspecified limit is guaranteed to be at least 2^31-1.

Definition at line 68 of file semaphore.

References L4::Triggerable::trigger().

Here is the call graph for this function:

---

The documentation for this struct was generated from the following file:

• l4/sys/semaphore