class Fifo_system

Class Fifo_system: Class that comprises the individual fifos.

Public Methods

Creation and removal of the fifo system and the fifos

Read/write and control access to the fifos

Access to information about the fifo system

Access to information about the fifos

Documentation

Class Fifo_system: Class that comprises the individual fifos. The fifos themselves are objects that reside in shared memory. The Fifo_sytem itself is an object in the local address space of the process and regulates the access to the fifos. This is necessary as different processes attach the same shared memory at different address locations.
The class Fifo_sytem allows to create and delete fifos, coordinates the read/write operations and can return various status information about the fifo system.
Note: This class (and not the Fifo class) controls all the shared resources that controls the access to the fifos.

Modifications:

• Initialise the pointers to the fifos in shared memory to NULL in the constructor to allow check in remove_fifo_system whether we actually succeeded to create the IPC resources as we attempt to delete them.
  CW Mar 17, 99

• Add empty_fifo member function.
  Notized that the garbage demon doesn't properly handle a process that crashed and leaves a non-empty fifo behind. We fix this by expanding delete_fifo such that it empties the fifo. The fifo_entries that are found in there will be put back into the INPUT fifo.
  CW Dec 7, 1999

Creation and removal of the fifo system and the fifos

Fifo_system(char* filename, int nfifos, int fifo_depth)

Creates the Fifo system. Creates/attaches to the shared memory and semaphores and (possibly) initialises them.

Parameters:

filename - : project file for the shared resources (see package otools)
nfifos - : maximum number of fifos.
fifo_depth - : default depth of the fifos.

~Fifo_system()

Destructor

int remove_fifo_system()

Removes the fifo system. The destructor only deletes the fifo system for the calling process and deletes the shared resources only if the calling process is the last one to detach. remove_fifo_system in contrast forces the removal of the system.

Fifo* create_fifo(const char* name, const char* type, Fifo::sFifo_mode mode, int slot_nb = -1)

Creates a fifo in the fifo system. Checks whether the fifo already exists or has to be created. If we attach to an existing fifo, check the mode.

Parameters:

name - : name of the fifo - see constructor of class fifo for details.
type - : type of the fifo - see constructor of class fifo for details.
mode - : mode of the fifo - see constructor of class fifo for details.
slot_nb - : index of the fifo in the array of fifos - see constructor of class fifo for details.

Returns:

Pointer fo the fifo or NULL.

int delete_fifo( Fifo* pFifo )

Delete the fifo pointed to by pFifo. Note that the INPUT fifo cannot be deleted.

int delete_fifo(const char* name )

Delete the fifo with the name name

int remove_fifo(const char* name)

Removes the fifo - same of delete - do not use - will become obsolte

int empty_fifo( Fifo* pFifo )

Empties a fifo. It reads all remaining fifo_entries in the fifo and releases them, i.e. they are put back into the INPUT fifo.

int empty_fifo( const char* pcFifoName )

Empties a fifo. It reads all remaining fifo_entries in the fifo and releases them, i.e. they are put back into the INPUT fifo.

Read/write and control access to the fifos

int write_fifo(const char* fifo_name, Fifo_entry &fev)

Write the fifo entry fev into the fifo named name.

Returns:

0 if success, -1 if error.

int write_fifo(Fifo* fifo, Fifo_entry &fev)

Write the fifo entry fev into the fifo pointed to by fifo.

Returns:

0 if success, -1 if error.

int read_fifo(const char* fifo_name, Fifo_entry &fev, int mode = -1 )

Read the fifo given by the string name.

Parameters:

- fifo_name name of the fifo
fev - reference to the fifo entry
mode - (optional) if not given then the default mode from the fifo header will be taken.

Returns:

0 if success, -1 if error.

int read_fifo(Fifo* fifo, Fifo_entry &fev, int mode = -1 )

Overloaded read_fifo to allow reading a fifo pointed to by a pointer

int unblock_fifo( const Fifo* fifo ) const

Unlocks the fifo pointed to by fifo

int unblock_fifo( const char* fifo_name ) const

Unlocks the named fifo

int lock()

Locks the entire fifo system.

int unlock()

Unlocks the entire fifo system.

Access to information about the fifo system

void print()

Prints system information to cout

int get_status() const

Returns the status of the system.

Returns:

unused, in_use, locking, locked, error

const char* get_name() const

Returns the name of the fifo system

pid_t get_creator() const

Returns the PID of the process that originally created the system

int get_nb_fifos() const

Returns the maximum number of fifos.

int get_fifo_depth() const

Returns the depth of the fifos.

int get_nproc_att() const

Returns the number of processes that are currently attached to the fifo.

Fifo* find_fifo(const char* name) const

Given the name of a fifo, return a pointer to it.

Access to information about the fifos

int get_nproc_waiting(const Fifo* fifo) const

Return the number of processes that are waiting on the fifo *fifo for events.

int get_nproc_waiting(const char* Fifo_name ) const

Return the number of processes that are waiting on the fifo Fifo_name for events.

int get_fifo_cnt( Fifo* fifo ) const

Return the number of events in the fifo *fifo.

int get_fifo_cnt( const char* Fifo_name ) const

Return the number of events in the fifo named Fifo_name.

int get_fifo_cnts( int &nFifos, int* &addr ) const

Get the number of events in every fifo. This member function returns the exact number of all the fifos at a given point (they are the semaphore counts of the system).

Parameters:

nFifos - reference to the number of fifos.
addr - reference to the address of the array with the values

Returns:

0 if success, -1 otherwise. Note: The client is responsible for deleting the array *addr.

int get_fifo_locks( int &nFifos, int* &addr ) const

Returns the lock semaphores for every fifo. The same note as get_fifo_cnts applies here.

This class has no child classes.

Friends:

class Fifo
class Fifo_iterator

Author:

C.Witzig
Date: Nov 20, 1997

Version:

Last update: Dec 7, 1999

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