Provided by: libbobcat-dev_4.08.06-1build1_amd64 bug

NAME

       FBB::SharedStream - I/O operations on shared memory

SYNOPSIS

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

DESCRIPTION

       This  class  combines the features of the std::istream and std::ostream classes, operating
       on shared memory. As with std::fstream objects, a seekp or seekg member call  is  required
       to switch from writing to reading or v.v.

       As  with  std::fstream objects, FBB::SharedStream objects do not keep separate offsets for
       reading and writing: the seek-members always refer to the (single)  offset  maintained  by
       the FBB::SharedMemory object to which the SharedStream object interfaces.

       So,  although  tellg  and  tellp return identical values, tellg should not be called after
       writing to a SharedStream object, and tellp should not be  called  after  reading  from  a
       SharedStream  object, as calling members related to reading (tellg) after writing and v.v.
       put the stream in its fail state.

NAMESPACE

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

INHERITS FROM

       FBB::SharedStreambuf (private inheritance),
       std::istream,
       std::ostream,
       FBB::SharedEnum__ (cf. sharedmemory(3bobcat) for a description of this 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      SharedStream():
              The   default  constructor  defines  a  stub  a  SharedStream  object  that  cannot
              immediately be used to access shared memory. To use it, its member open must  first
              be called.

       o      SharedStream(size_t  maxSize,  SizeUnit  sizeUnit,  std::ios::openmode  openMode  =
              std::ios::in | std::ios::out, size_t access = 0600):
              This constructor creates a stream inheriting the facilities of an std::istream  and
              std::ostream  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 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.

       o      SharedStream(int id, std::ios::openmode openMode = std::ios::in | std::ios::out):
              This constructor creates a stream inheriting the facilities of an std::istream  and
              std::ostream that connects to a shared memory segment having ID id.

              Specifying  the  ios::trunc  flag  immediately  clears  the  contents 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 are not available.

OVERLOADED OPERATORS

              No overloaded move and copy assignment operators are available.

MEMBER FUNCTIONS

              All  members  of  std::istream and std::ostream and the enum values kB, MB, and GB,
              defined by FBB::SharedEnum__ 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 SharedStream object interfaces.  This member does not alter the value
              returned by the stream’s tellg and tellp members.

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

       o      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)).  Creating  a
              SharedCondition  object does not alter the value returned by the stream’s tellg and
              tellp members.

              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::SharedStream 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  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. Following the  information  about
              the shared memory, end is inserted into out.

       o      void   open(size_t   maxSize,  SizeUnit  sizeUnit,  std::ios::openmode  openMode  =
              std::ios::in | std::ios::out, 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::SharedStream. A
              matching close member does not exist and is not required.

              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 opening fails, an FBB::Exception is thrown.

       o      void open(int id, std::ios::openmode openMode = std::ios::in | std::ios::out):
              This member connects the FBB::SharedStream 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.

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

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

       o      void remove():
              The shared memory is first locked. Next, all  shared  memory  is  returned  to  the
              operating  system.  The  FBB::SharedStream  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

       #include <iostream>
       #include <string>
       #include <ostream>
       #include <istream>

       #include <bobcat/exception>
       #include <bobcat/sharedstream>
       #include <bobcat/sharedcondition>

       using namespace std;
       using namespace FBB;

       int main()
       {
           SharedStream sharedStream;

           int id = -1;

           while (true)
           {
               cout <<
                       "\n"
                       " K             kill (no lock) existing shared segment\n"
                       " S             show stats of current shared segment\n"
                       " L <id>        Load segment <id>\n"
                       " C             Install a SharedCondition at offset 0\n"
                       " c            create new shared memory (sets id)\n"
       //                " l            lock segment id until key pressed\n"
       //                " p <x> c      put char c at offset x\n"
                       " q            quit\n"
       //                " r <x> <n>    read n chars from offset x\n"
       //                " w <x> args   write all args at offset x\n"
                         " i            insert lines (until empty) at the current "
                                                                       "offset\n"

                         " x            extract lines (until EOF) from the current "
                                                                       "offset\n"
                         " X            extract the next line from the current "
                                                                       "offset\n"
                         "              when nodified via ’N’\n"
                         " N            notify a waiting X\n"
                         " s <x>        seek (abs) offset x\n"
                       "? ";

               char ch;
               cin >> ch;

               ios::off_type offset;

               cout << "Requested: " << ch << ’\n’;

               sharedStream.clear();

               switch (ch)
               {
                   case ’c’:
                   {
                       sharedStream.open(1, SharedStream::kB);

                       id = sharedStream.id();
                       cout << "id = " << id << ’\n’;
                       sharedStream.memInfo(cout);
                       cout << ’\n’;
                   }
                   break;

                   case ’C’:
                   {
                       sharedStream.seekp(0);
                       SharedCondition cond(sharedStream.createSharedCondition());
                       sharedStream.seekg(cond.width());
                       break;
                   }

                   case ’K’:         // delete segment
                   {
                       if (id == -1)
                       {
                           cout << "No segment loaded\n";
                           continue;
                       }

                       cout << "Removing segment id = " << id << ’\n’;
                       if (ch == ’R’)
                           sharedStream.remove();
                       else
                           sharedStream.kill();

                       id = -1;
                   }
                   break;

                   case ’L’:
                       cin >> id;
                       cout << "Loading segment " << id << ’\n’;
                       sharedStream.open(id);
                       sharedStream.memInfo(cout);
                       cout << ’\n’;
                   break;

                   case ’S’:
                       if (id == -1)
                       {
                           cout << "No segment loaded\n";
                           continue;
                       }
                       sharedStream.memInfo(cout);
                       cout << ’\n’;
                   break;

                   case ’s’:
                   {
                       size_t offset;
                       if (id == -1)
                       {
                           cout << "No segment loaded\n";
                           continue;
                       }
                       cin >> offset;
                       sharedStream.seekg(offset);
                       sharedStream.seekp(offset);
                       cout << "tellg: " << sharedStream.tellg() << ", "
                               "tellp: " << sharedStream.tellp() << ’\n’;
                   }
                   break;

                   case ’i’:
                   {
                       string line;
                       getline(cin, line);
                       sharedStream.seekp(0, ios::cur);
                       while (true)
                       {
                           cout << "? ";
                           if (not getline(cin, line) || line.empty())
                               break;
                           sharedStream << line << endl;
                           cout <<
                                   "   tellp: " << sharedStream.tellp() << ’\n’;
                       }
                           cout << // "   tellg: " << sharedStream.tellg() << ", "
                                   "   tellp: " << sharedStream.tellp() << ’\n’;
                   }
                   break;

                   case ’x’:
                   {
                       string line;
                       sharedStream.seekg(0, ios::cur);

                       while (true)
                       {
                           cout << ": ";
                           if (not getline(sharedStream, line))
                               break;
                           cout << line << "\n"
                                   "   tellg: " << sharedStream.tellg() << ", "
                                   "   tellp: " << sharedStream.tellp() << ’\n’;
                       }
                   }
                   break;

                   case ’X’:
                   {
                       SharedCondition cond(sharedStream.attachSharedCondition(0));

                       string line;
                       sharedStream.seekg(cond.width());

                       cond.lock();

                       while (true)
                       {
                           cond.wait();

                           cout << ": ";
                           if (not getline(sharedStream, line))
                               break;

                           cout << line << "\n"
                                   "   tellg: " << sharedStream.tellg() << ", "
                                   "   tellp: " << sharedStream.tellp() << ’\n’;
                       }
                       cout << "All done\n";
                       cond.unlock();
                   }
                   break;

                   case ’N’:
                   {
                       string line;
                       getline(cin, line);

                       SharedCondition cond(sharedStream.attachSharedCondition(0));
                       while (true)
                       {
                           cout << "’enter’ or ’q’? ";
                           getline(cin, line);

                           if (line == "q")
                               break;

                           cond.lock();
                           cond.notify();
                           cond.unlock();
                       }
                   }
                   break;

                   case ’p’:           // put a char behind the last written
                   {
                       if (id == -1)
                       {
                           cout << "No segment loaded\n";
                           continue;
                       }

                       cin >> offset >> ch;
                       if (!cin)
                           throw Exception() << "cmd specification error";

                       sharedStream.seekp(offset);
                       cout << "Segment id = " << id << " at write offset " <<
                                                           sharedStream.tellp() << ’\n’;
                       sharedStream.put(ch);
                   }
                   break;

                   case ’r’:           // put a char behind the last written
                   {
                       if (id == -1)
                       {
                           cout << "No segment loaded\n";
                           continue;
                       }

                       int n;

                       cin >> offset >> n;
                       if (!cin)
                           throw Exception() << "cmd specification error";

                       char buf[n];

                       sharedStream.seekg(offset);
                       cout << "Segment id = " << id << " at offset " <<
                                sharedStream.tellg() << ", to read " << n << " bytes\n";

                       n = sharedStream.read(buf, n).gcount();

                       if (n < 0)
                           cout << "No data at " << offset << ’\n’;
                       else
                       {
                           cout << "Retrieved " << n << " bytes, containing `";
                           cout.write(buf, n);
                           cout << "’\n";

                           for (auto ch: buf)
                               cout << static_cast<int>(ch) << ’ ’;
                           cout << ’\n’;
                       }
                   }
                   break;

                   case ’w’:           // write chars at offset
                   {
                       if (id == -1)
                       {
                           cout << "No segment loaded\n";
                           continue;
                       }

                       string line;

                       cin >> offset;
                       getline(cin, line);
                       if (!cin)
                           throw Exception() << "cmd specification error";

                       streampos pos = sharedStream.seekp(offset).tellp();

                       cout << "Segment id = " << id << " at offset " <<
                                pos << ", to write " << line.length() << " bytes\n";

                       sharedStream.write(line.data(), line.length());

                       if (!sharedStream)
                           cout << "No room left to write any bytes\n";
                       else
                           cout << "Wrote " << (sharedStream.tellp() - pos) << " bytes\n";
                   }
                   break;

                   case ’q’:
                   return 0;

                   default:
                       cout << "request not implemented: " << ch << ’\n’;
                   break;
               }
           }
       }

FILES

       bobcat/sharedstream - defines the class interface

SEE ALSO

       bobcat(7),         chmod(1),        isharedstream(3bobcat),        osharedstream(3bobcat),
       sharedblock(3bobcat),           sharedcondition(3bobcat),            sharedmemory(3bobcat)
       sharedmutex(3bobcat), sharedpos(3bobcat), sharedsegment(3bobcat), sharedstreambuf(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_4.08.06-x.dsc: detached signature;

       o      bobcat_4.08.06-x.tar.gz: source archive;

       o      bobcat_4.08.06-x_i386.changes: change log;

       o      libbobcat1_4.08.06-x_*.deb: debian package holding the libraries;

       o      libbobcat1-dev_4.08.06-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).