# FBB::SharedBuf(3bobcat)

## Shared memory streambuf
(libbobcat-dev_6.07.01)

## 2005-2025

## NAME

FBB::SharedBuf - streambuf interfacing to shared memory

## SYNOPSIS

#include <bobcat/sharedbuf>
Linking option: -lpthread -lbobcat

## DESCRIPTION

This class implements a specialization of the std::streambuf class, allowing stream classes (std::istream, std::ostream, FBB::ISharedStream, FBB::OSharedStream and FBB::SharedStream) to perform I/O operations on shared memory. FBB::SharedBuf objects interface to a FBB::SharedMemory objects.

## NAMESPACE

FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

## INHERITS FROM

std::streambuf, FBB::SharedEnum__ (cf. sharedmemory(3bobcat) for a description of the latter class).

## SIZEUNIT ENUMERATION

The enum SizeUnit defines the following symbolic constants:

- kB, representing 1024 (2**10) bytes of memory;
- MB, representing 1048576 (2**20) bytes of memory;
- GB, representing 1073741824 (2**30) bytes of memory

## CONSTRUCTORS

- SharedBuf():
  The default constructor defines a stub SharedBuf object that cannot immediately be used to access shared memory. Before it can be used by, shared stream classes like FBB::SharedStream, its member setMemory must first have been called.

- SharedBuf(size_t maxSize, SizeUnit sizeUnit, std::ios::openmode openMode = std::ios::in | std::ios::out, size_t access = 0600):
  This constructor creates a shared memory segment having a capacity of at least maxSize * sizeUnit bytes.

  By default, the shared memory segment is opened for reading and writing. Different from the open modes used for file streams, creating a shared memory stream with open modes ios::in | ios::out is OK. In this case the shared memory segment is created and once information has been written to the shared memory it can also be read again.

  The shared memory's access rights are defined by the access parameter, interpreted as an octal value, using the well-known (chmod(1)) way to define the access rights for owner, group and others.

  If construction fails, an FBB::Exception is thrown.

- SharedBuf(int id, std::ios::openmode openMode = std::ios::in | std::ios::out):
  This constructor connects to a shared memory segment having ID id.

  Specifying the ios::trunc flag immediately clears the content of the shared memory.

  An FBB::Exception is thrown if construction fails (e.g., no shared memory segment having ID id exists),

Copy and move constructors (and assignment operators) are not available.

## MEMBER FUNCTIONS

All members of std::streambuf and the enum values kB, MB, and GB, defined by FBB::SharedEnum__ are available.

- void clear():
  The shared memory is first locked. Next, all shared data segment are returned to the operating system, after which the shared memory segment is unlocked again. Returning from clear the shared memory The FBB::SharedMemory object is effectively re-initialized, with offset and nReadable returning 0.

- int id() const:
  The ID of the shared memory segment is returned.

- void kill():
  Without locking the shared memory the FBB::SharedBuf's shared memory is deleted. The FBB::SharedBuf object is unusable after returning from kill.

- void memInfo(std::ostream &out):
  Information about the SharedMemory object is inserted into the provide ostream object. The IDs of the shared segments, their sizes, the maximum number of shared memory segments, the number of bytes that can be read from the shared memory, and its actual storage capacity, etc., are displayed. The inserted information is not terminated by a final newline character.

- void remove():
  The shared memory is locked, and the FBB::SharedBuf's shared memory is deleted. The FBB::SharedBuf object is unusable after returning from remove.

- void setMemory(SharedMemory &&tmp):
  The anonymous temporary SharedMemory object that is passed to setMemory defines the new shared memory segment to which the FBB::SharedBuf object interfaces. It can also be called to reuse a FBB::SharedBuf object again after calling kill or remove.

- FBB::SharedMemory &sharedMemory():
  A reference to the FBB::SharedMemory object to which the FBB::SharedBuf object interfaces is returned.

## PROTECTED MEMBER FUNCTIONS

- FBB::SharedCondition attachSharedCondition(std::ios::off_type offset, std::ios::seekdir origin):
  Returns an FBB::SharedCondition(3) object, interfacing to a shared condition variable located at offset offset (relative to origin) in the SharedMemory object to which the SharedStreamBuf object interfaces.

  An FBB::Exception is thrown if the FBB::SharedCondition object could not be constructed.

- FBB::SharedCondition createSharedCondition():
  Returns an FBB::SharedCondition(3) object, interfacing to a newly created shared condition variable which is created at the current offset of the SharedMemory object to which the SharedStream object interfaces (or at the first offset of the next physical shared memory data block, cf. sharedcondition(3bobcat))

.

An FBB::Exception is thrown if the FBB::SharedCondition object could not be constructed.

- void setOpenMode(std::ios::openmode flag):
  The streambuf's openmode is changed to the settings defined by flag. This member is used by, e.g., SharedStream::open, to adapt the FBB::SharedBuf's openmode to the flags that are passed to open.

- FBB::SharedMemory &sharedMemory():
  Returns a reference to the FBB::SharedMemory object to which the SharedBuf object interfaces.

## EXAMPLE

See the sharedstream(3bobcat) man page.

## FILES

bobcat/sharedbuf - defines the class interface

## SEE ALSO

bobcat(7), chmod(1), isharedstream(3bobcat), osharedstream(3bobcat), sharedblock(3bobcat), sharedcondition(3bobcat), sharedmemory(3bobcat) sharedmutex(3bobcat), sharedpos(3bobcat), sharedreadme(7bobcat), sharedsegment(3bobcat), sharedstream(3bobcat)

## BUGS

Note that by default exceptions thrown from within a std::stream object are caught by the stream object, setting its ios::failbit flag. To allow exceptions to leave a stream object, its exceptions member can be called, e.g., using:

        myStream.exceptions(ios::failbit | ios::badbit | ios::eofbit);

## BOBCAT PROJECT FILES

- https://fbb-git.gitlab.io/bobcat/: gitlab project page;

Debian Bobcat project files:

- libbobcat6: debian package containing the shared library, changelog and copyright note;
- libbobcat-dev: debian package containing the static library, headers, manual pages, and developer info;

## BOBCAT

Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.

## COPYRIGHT

This is free software, distributed under the terms of the GNU General Public License (GPL).

## AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).