FBB::ISharedStream - std::istream operations on shared memory
#include <bobcat/isharedstream>
Linking option: -lpthread -lbobcat
This class offers the features of the std::istream class,
operating on shared memory.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
FBB::ISharedBuf (private inheritance),
std::istream,
FBB::SharedEnum__ (cf. sharedmemory(3bobcat) for a description
of this last base class).
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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- 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.
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- 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.
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- 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.
All members of std::istream, and the enum values
kB, MB, and GB, defined by FBB::ISharedEnum__ are
available.
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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
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.
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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 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
bobcat/isharedstream - defines the class interface
bobcat(7), chmod(1), osharedstream(3bobcat),
sharedblock(3bobcat), sharedcondition(3bobcat),
sharedmemory(3bobcat), sharedmutex(3bobcat),
sharedpos(3bobcat), sharedreadme(7bobcat),
sharedsegment(3bobcat), sharedstream(3bobcat),
sharedbuf(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_5.07.00-x.dsc: detached signature;
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- bobcat_5.07.00-x.tar.gz: source archive;
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- bobcat_5.07.00-x_i386.changes: change log;
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- libbobcat1_5.07.00-x_*.deb: debian package containing the
libraries;
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- libbobcat1-dev_5.07.00-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).