/usr/share/doc/libbobcat3-dev/man/sharedstream.3.html

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<title>FBB::SharedStream</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<h1>FBB::SharedStream</h1>
<h2>libbobcat-dev_3.19.01-x.tar.gz</h2>
<h2>2005-2013</h2>

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<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<title>FBB::SharedStream(3bobcat)</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<h1>FBB::SharedStream(3bobcat)</h1>
<h2>libbobcat-dev_3.19.01-x.tar.gz I/O on shared memory</h2>
<h2>2005-2013</h2>


<p>
<h2>NAME</h2>FBB::SharedStream - I/O operations on shared memory
<p>
<h2>SYNOPSIS</h2>
    <strong>#include &lt;bobcat/sharedstream&gt;</strong><br>
    Linking option: <em>-lpthread -lbobcat</em> 
<p>
<h2>DESCRIPTION</h2>
<p>
This class combines the features of the <strong>std::istream</strong> and
<strong>std::ostream</strong> classes, operating on shared memory. As with <em>std::fstream</em>
objects, a <em>seekp</em> or <em>seekg</em> member call is required to switch from
writing to reading or v.v.
<p>
<h2>NAMESPACE</h2>
    <strong>FBB</strong><br>
    All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace <strong>FBB</strong>.
<p>
<h2>INHERITS FROM</h2>
    <strong>FBB::SharedStreambuf</strong> (private inheritance),<br>
    <strong>std::istream</strong>,<br>
    <strong>std::ostream</strong>,<br>
    <strong>FBB::SharedEnum__</strong> (cf. <strong>sharedmemory</strong>(3bobcat) for a description of
        this last base class).
<p>
<h2>CONSTRUCTORS</h2>
    <ul>
    <li> <strong>SharedStream()</strong>:<br>
       The default constructor defines a stub a <strong>SharedStream</strong> object that
        cannot immediately be used to access shared memory. To use it, its
        member <em>open</em> must first be called.
<p>
<li> <strong>SharedStream(size_t maxSize, SizeUnit sizeUnit, 
            std::ios::openmode openMode = std::ios::in | std::ios::out,
            size_t access = 0600)</strong>:<br>
       This constructor creates a stream inheriting the facilities of an
        <em>std::istream</em> and <em>std::ostream</em> that interfaces to a shared
        memory segment having a capacity of at least <em>maxSize * sizeUnit</em>
        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 <em>ios::in | ios::out</em> 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 <em>access</em>
        parameter, using the well-known (<strong>chmod</strong>(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 <em>FBB::Exception</em> is thrown.
<p>
<li> <strong>SharedStream(int id, std::ios::openmode openMode = std::ios::in |
        std::ios::out)</strong>:<br> 
       This constructor creates a stream inheriting the facilities of an
        <em>std::istream</em> and <em>std::ostream</em> that connects to a shared memory
        segment having ID <em>id</em>. If construction succeeds the shared memory
        is ready for use. If construction fails (e.g., no shared memory
        segment having ID <em>id</em> exists), an <em>FBB::Exception</em> is
        thrown. Specifying the <em>ios::trunc</em> flag immediately clears the
        contents of the shared memory.
    </ul>
    Copy and move constructors are not available.
<p>
<h2>OVERLOADED OPERATORS</h2>
<p>
The overloaded move and copy assignment operators are not available.
<p>
<h2>MEMBER FUNCTIONS</h2>
<p>
All members of <em>std::istream</em> and <em>std::ostream</em> and the <em>enum</em>
values <em>kB, MB</em>, and <em>GB</em>, defined by <em>FBB::SharedEnum__</em> are available. 
<p>
<ul>
    <li> <strong>void clear()</strong>:<br>
       This member clears the error states of the <em>std::istream</em>
        and <em>std::ostream</em> base class objects.
<p>
<li> <strong>int id() const</strong>:<br>
       The ID of the shared memory segment is returned.
<p>
<li> <strong>void kill()</strong>:<br>
       Without locking the shared memory first,  all shared memory is returned
        to the operating system. The <strong>FBB::SharedStream</strong> object is unusable
        after returning from <em>kill</em>. Other processes that were using the
        shared memory can continue to do so.
<p>
<li> <strong>void remove()</strong>:<br>
       The shared memory is first locked. Next, all shared memory is returned
        to the operating system. The <strong>FBB::SharedStream</strong> object is unusable
        after returning from <em>remove</em>. Other processes that were using the
        shared memory can continue to do so.
<p>
<li> <strong>void memInfo(std::ostream &amp;out, char const *end = "\n")</strong>:<br>
       Information about the <em>SharedMemory</em> object is inserted into the
        provide <em>ostream</em> 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, <em>end</em> is inserted into <em>out</em>.
<p>
<li> <strong>void open(size_t maxSize, SizeUnit sizeUnit,
            std::ios::openmode openMode = std::ios::in | std::ios::out,
            size_t access = 0600)</strong>:<br>
       This member creates a shared memory segment having a capacity of at
        least <em>maxSize * sizeUnit</em> bytes, and connects the shared memory
        segment to the <strong>FBB::SharedStream</strong>. A matching <em>close</em> 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
        <em>ios::in | ios::out</em> 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 <em>access</em> parameter, using the well-known
        (<strong>chmod</strong>(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 <em>FBB::Exception</em> is
        thrown.
<p>
<li> <strong>void open(int id, std::ios::openmode openMode = std::ios::in |
        std::ios::out)</strong>:<br> 
       This member connects the <strong>FBB::SharedStream</strong> object to a shared
        memory segment having ID <em>id</em>. A matching <em>close</em> 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 <em>id</em> exists), an <em>FBB::Exception</em> is
        thrown. Specifying the <em>ios::trunc</em> flag immediately clears the
        contents of the shared memory.
    </ul>
<p>
<h2>EXAMPLE</h2>
<p>
<pre>
#include &lt;iostream&gt;
#include &lt;string&gt;
#include &lt;ostream&gt;
#include &lt;istream&gt;

#include &lt;bobcat/exception&gt;
#include &lt;bobcat/sharedstream&gt;

using namespace std;
using namespace FBB;

int main()
{
    SharedStream shared;

    int id = -1;

    while (true)
    {
        cout &lt;&lt; 
                "\n"
                " K             kill (no lock) existing shared segment\n"
                " R             remove existing shared segment\n"
                " S             show stats of current shared segment\n"
                " L &lt;id&gt;        Load segment &lt;id&gt;\n"
                " c            create new shared memory (sets id)\n"
                " l            lock segment id until key pressed\n"
                " p &lt;x&gt; c      put char c at offset x\n"
                " q            quit\n"
                " r &lt;x&gt; &lt;n&gt;    read n chars from offset x\n"
                " w &lt;x&gt; args   write all args at offset x\n"
                "? ";

        char ch;
        cin &gt;&gt; ch;

        ios::off_type offset;

        cout &lt;&lt; "Requested: " &lt;&lt; ch &lt;&lt; '\n';

        shared.clear();

        switch (ch)
        {
            case 'c':
            {
                shared.open(1, SharedStream::kB);

                id = shared.id();
                cout &lt;&lt; "id = " &lt;&lt; id &lt;&lt; '\n';
                shared.memInfo(cout);
                cout &lt;&lt; '\n';
            }
            break;
        
            case 'K':         // delete segment
            case 'R':         // delete segment
            {
                if (id == -1)
                {
                    cout &lt;&lt; "No segment loaded\n";
                    continue;
                }

                cout &lt;&lt; "Removing segment id = " &lt;&lt; id &lt;&lt; '\n';
                if (ch == 'R')
                    shared.remove();
                else
                    shared.kill();

                id = -1;
            }
            break;

            case 'L':
                cin &gt;&gt; id;
                cout &lt;&lt; "Loading segment " &lt;&lt; id &lt;&lt; '\n';
                shared.open(id);
                shared.memInfo(cout);
                cout &lt;&lt; '\n';
            break;

            case 'S':
                if (id == -1)
                {
                    cout &lt;&lt; "No segment loaded\n";
                    continue;
                }
                shared.memInfo(cout);
                cout &lt;&lt; '\n';
            break;
            
            case 'p':           // put a char behind the last written
            {
                if (id == -1)
                {
                    cout &lt;&lt; "No segment loaded\n";
                    continue;
                }

                cin &gt;&gt; offset &gt;&gt; ch;
                if (!cin)
                    throw Exception() &lt;&lt; "cmd specification error";
    
                shared.seekp(offset);
                cout &lt;&lt; "Segment id = " &lt;&lt; id &lt;&lt; " at write offset " &lt;&lt; 
                                                    shared.tellp() &lt;&lt; '\n';
                shared.put(ch);
            }
            break;
                
            case 'r':           // put a char behind the last written
            {
                if (id == -1)
                {
                    cout &lt;&lt; "No segment loaded\n";
                    continue;
                }

                int n;

                cin &gt;&gt; offset &gt;&gt; n;
                if (!cin)
                    throw Exception() &lt;&lt; "cmd specification error";

                char buf[n];

                shared.seekg(offset);
                cout &lt;&lt; "Segment id = " &lt;&lt; id &lt;&lt; " at offset " &lt;&lt; 
                         shared.tellg() &lt;&lt; ", to read " &lt;&lt; n &lt;&lt; " bytes\n";
    
                n = shared.read(buf, n).gcount();
    
                if (n &lt; 0)
                    cout &lt;&lt; "No data at " &lt;&lt; offset &lt;&lt; '\n';
                else
                {
                    cout &lt;&lt; "Retrieved " &lt;&lt; n &lt;&lt; " bytes, containing `";
                    cout.write(buf, n);
                    cout &lt;&lt; "'\n";
    
                    for (auto ch: buf)
                        cout &lt;&lt; static_cast&lt;int&gt;(ch) &lt;&lt; ' ';
                    cout &lt;&lt; '\n';
                }
            }
            break;
                
            case 'w':           // write chars at offset
            {
                if (id == -1)
                {
                    cout &lt;&lt; "No segment loaded\n";
                    continue;
                }

                string line;

                cin &gt;&gt; offset;
                getline(cin, line);
                if (!cin)
                    throw Exception() &lt;&lt; "cmd specification error";
    
                streampos pos = shared.seekp(offset).tellp();

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

                if (!shared)
                    cout &lt;&lt; "No room left to write any bytes\n";
                else
                    cout &lt;&lt; "Wrote " &lt;&lt; (shared.tellp() - pos) &lt;&lt; " bytes\n";
            }
            break;
                
            case 'q':
            return 0;

            default:
                cout &lt;&lt; "request not implemented: " &lt;&lt; ch &lt;&lt; '\n';
            break;
        }
    }
}

</pre>

<p>
<h2>FILES</h2>
    <em>bobcat/sharedstream</em> - defines the class interface
<p>
<h2>SEE ALSO</h2>
    <strong>bobcat</strong>(7),  <strong>chmod</strong>(1),
        <strong>isharedstream</strong>(3bobcat),
        <strong>osharedstream</strong>(3bobcat),
        <strong>sharedblock</strong>(3bobcat), 
        <strong>sharedmemory</strong>(3bobcat)
        <strong>sharedmutex</strong>(3bobcat), 
        <strong>sharedpos</strong>(3bobcat), 
        <strong>sharedsegment</strong>(3bobcat),
        <strong>sharedstreambuf</strong>(3bobcat)
<p>
<h2>BUGS</h2>
    Note that by default exceptions thrown from within a <strong>std::stream</strong>
object are caught by the stream object, setting its <em>ios::failbit</em> flag. To
allow exceptions to leave a stream object, its <em>exceptions</em> member can be
called, e.g., using:
        <pre>

    myStream.exceptions(ios::failbit | ios::badbit | ios::eofbit);
        
</pre>

<p>

<h2>DISTRIBUTION FILES</h2>
    <ul>
    <li> <em>bobcat_3.19.01-x.dsc</em>: detached signature;
    <li> <em>bobcat_3.19.01-x.tar.gz</em>: source archive;
    <li> <em>bobcat_3.19.01-x_i386.changes</em>: change log;
    <li> <em>libbobcat1_3.19.01-x_*.deb</em>: debian package holding the
            libraries;
    <li> <em>libbobcat1-dev_3.19.01-x_*.deb</em>: debian package holding the
            libraries, headers and manual pages;
    <li> <em>http://sourceforge.net/projects/bobcat</em>: public archive location;
    </ul>
<p>
<h2>BOBCAT</h2>
    Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
<p>
<h2>COPYRIGHT</h2>
    This is free software, distributed under the terms of the 
    GNU General Public License (GPL).
<p>
<h2>AUTHOR</h2>
    Frank B. Brokken (<strong>f.b.brokken@rug.nl</strong>).
<p>
libbobcat-dev 3.19.01-1ubuntu1 / usr / share / doc / libbobcat3-dev / man / sharedstream.3.html
