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::ISharedStreambuf (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:
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
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.
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.
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 are not available.
OVERLOADED OPERATORS
The overloaded move and copy 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.
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.
int id() const:
The ID of the shared memory segment is returned.
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.
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.
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.
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.
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.
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
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: