FBB::SharedBuf - streambuf interfacing to shared memory
#include <bobcat/sharedbuf>
Linking option: -lpthread -lbobcat
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.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
The enum SizeUnit defines the following symbolic
constants:
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- kB, representing 1024 (2**10) bytes of memory;
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- MB, representing 1048576 (2**20) bytes of memory;
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- GB, representing 1073741824 (2**30) bytes of memory
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- 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.
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- 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.
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- 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.
All members of std::streambuf and the enum values
kB, MB, and GB, defined by FBB::SharedEnum__ are
available.
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- 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.
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- int id() const:
The ID of the shared memory segment is returned.
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- 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.
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- 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.
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- 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.
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- 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.
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- FBB::SharedMemory &sharedMemory():
A reference to the FBB::SharedMemory object to which the
FBB::SharedBuf object interfaces is returned.
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- 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.
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- 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.
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- 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.
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- FBB::SharedMemory &sharedMemory():
Returns a reference to the FBB::SharedMemory object to which the
SharedBuf object interfaces.
bobcat/sharedbuf - defines the class interface
bobcat(7), chmod(1), isharedstream(3bobcat),
osharedstream(3bobcat), sharedblock(3bobcat),
sharedcondition(3bobcat), sharedmemory(3bobcat)
sharedmutex(3bobcat), sharedpos(3bobcat),
sharedreadme(7bobcat), sharedsegment(3bobcat),
sharedstream(3bobcat)
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);
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- https://fbb-git.gitlab.io/bobcat/: gitlab project page;
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- bobcat_6.02.02-x.dsc: detached signature;
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- bobcat_6.02.02-x.tar.gz: source archive;
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- bobcat_6.02.02-x_i386.changes: change log;
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- libbobcat1_6.02.02-x_*.deb: debian package containing the
libraries;
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- libbobcat1-dev_6.02.02-x_*.deb: debian package containing the
libraries, headers and manual pages;
Bobcat is an acronym of `Brokken’s Own Base Classes And
Templates’.
This is free software, distributed under the terms of the GNU
General Public License (GPL).
Frank B. Brokken (f.b.brokken@rug.nl).