focal (3) isharedstream.3bobcat.gz
NAME
FBB::ISharedStream - std::istream operations on shared memory
SYNOPSIS
#include <bobcat/isharedstream>
Linking option: -lpthread -lbobcat
DESCRIPTION
This class offers the features of the std::istream class, operating on shared memory.
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the
namespace FBB.
INHERITS FROM
FBB::ISharedBuf (private inheritance),
std::istream,
FBB::SharedEnum__ (cf. sharedmemory(3bobcat) for a description of this last base class).
SIZEUNIT ENUMERATION
The enum SizeUnit defines the following symbolic constants:
o kB, representing 1024 (2**10) bytes of memory;
o MB, representing 1048576 (2**20) bytes of memory;
o GB, representing 1073741824 (2**30) bytes of memory
CONSTRUCTORS
o ISharedStream():
The default constructor defines a stub a ISharedStream object that cannot immediately be used to
access shared memory. To use it, its member open must first be called.
o ISharedStream(size_t maxSize, SizeUnit sizeUnit, std::ios::openmode openMode = std::ios::in,
size_t access = 0600):
This constructor creates an std::istream that interfaces to a shared memory segment having a
capacity of at least maxSize * sizeUnit bytes. By default, the shared memory segment is opened for
reading. Different from the open modes used for file streams, creating a shared memory stream with
open modes ios::in is OK. In this case the shared memory segment is created and once information
has been written to the shared memory by another process (or object) the information can be read.
The shared memory’s access rights are defined by the access parameter, using the well-known
(chmod(1)) way to define the access rights for the owner, the group and others, using octal
digits. If construction succeeds the shared memory is ready for use. If construction fails, an
FBB::Exception is thrown.
o ISharedStream(int id, std::ios::openmode openMode = std::ios::in):
This constructor creates an std::istream that connects to a shared memory segment having ID id. If
construction succeeds the shared memory is ready for use. If construction fails (e.g., no shared
memory segment having ID id exists), an FBB::Exception is thrown.
Copy and move constructors (and assignment operators) are not available.
MEMBER FUNCTIONS
All members of std::istream, and the enum values kB, MB, and GB, defined by FBB::ISharedEnum__ are
available.
o 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 ISharedStream object
interfaces. This member does not alter the value returned by the stream’s tellg member.
An FBB::Exception is thrown if the FBB::SharedCondition object could not be constructed.
o int id() const:
The ID of the shared memory segment is returned.
o void kill():
Without locking the shared memory first, all shared memory is returned to the operating system.
The FBB::ISharedStream object is unusable after returning from kill. Other processes that were
using the shared memory can continue to do so.
o void memInfo(std::ostream &out, char const *end = "\n"):
Information about the ISharedMemory 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. Following the information about the shaed memory, end is inserted into out.
o void open(size_t maxSize, SizeUnit sizeUnit, std::ios::openmode openMode = std::ios::in, size_t
access = 0600):
This member creates a shared memory segment having a capacity of at least maxSize * sizeUnit
bytes, and connects the shared memory segment to the FBB::ISharedStream. A matching close member
does not exist and is not required. By default, the shared memory segment is opened for reading.
Different from the open modes used for file streams, creating a shared memory stream with open
modes ios::in is OK. In this case the shared memory segment is created and once information has
been written to the shared memory by another process it can be read. The shared memory’s access
rights are defined by the access parameter, using the well-known (chmod(1)) way to define the
access rights for the owner, the group and others, using octal digits. If opening succeeds the
shared memory is ready for use. If opening fails, an FBB::Exception is thrown.
o void open(int id, std::ios::openmode openMode = std::ios::in):
This member connects the FBB::ISharedStream object to a shared memory segment having ID id. A
matching close member does not exist and is not required. If opening succeeds the shared memory is
ready for use. If opening fails (e.g., no shared memory segment having ID id exists), an
FBB::Exception is thrown.
o void remove():
The shared memory is first locked. Next, all shared memory is returned to the operating system.
The FBB::ISharedStream object is unusable after returning from remove. Other processes that were
using the shared memory can continue to do so.
o bool truncate(std::streamsize offset):
If offset is not exceeding the value returned by seekg(0, std::ios::end), then this latter value
is changed to offset and true is returned. Otherwise false is returned, and the value returned by
seekg is not altered. If the value returned by tellg exceeded offset, tellg’s return value it is
reduced to offset as well. Subsequent read operations on the shared memory can only succeed as
long as tellg’s return value hasn’t reached the value offset.
EXAMPLE
See the sharedstream(3bobcat) man page.
FILES
bobcat/isharedstream - defines the class interface
SEE ALSO
bobcat(7), chmod(1), osharedstream(3bobcat), sharedblock(3bobcat), sharedcondition(3bobcat), sharedmemory(3bobcat), sharedmutex(3bobcat), sharedpos(3bobcat), sharedreadme(7bobcat), sharedsegment(3bobcat), sharedstream(3bobcat), sharedbuf(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);
DISTRIBUTION FILES
o bobcat_5.02.00-x.dsc: detached signature;
o bobcat_5.02.00-x.tar.gz: source archive;
o bobcat_5.02.00-x_i386.changes: change log;
o libbobcat1_5.02.00-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_5.02.00-x_*.deb: debian package holding the libraries, headers and manual pages;
o http://sourceforge.net/projects/bobcat: public archive location;
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).