/usr/include/dballe/core/structbuf.h is in libdballe-dev 7.21-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 | /*
* core/structbuf - memory or file-backed storage of structures
*
* Copyright (C) 2014 ARPA-SIM <urpsim@smr.arpa.emr.it>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* Author: Enrico Zini <enrico@enricozini.com>
*/
#ifndef DBALLE_CORE_STRUCTBUF_H
#define DBALLE_CORE_STRUCTBUF_H
#include <wreport/error.h>
#include <cstdlib>
#include <unistd.h>
#include <sys/mman.h>
namespace dballe {
namespace structbuf {
int make_anonymous_tmpfile();
void write_buffer(int fd, void* buf, size_t size);
}
/**
* Buffer of simple structures that becomes file backed if it grows beyond a
* certain size.
*
* bufsize is the number of T items that we keep in memory before becoming
* file-backed.
*/
template<typename T, int bufsize=1024>
class Structbuf
{
protected:
/**
* In-memory buffer using during appending. When it becomes full, it is
* flushed out to a temporary file.
*/
T* membuf = nullptr;
/// Number of items in membuf
unsigned membuf_last = 0;
/**
* Memory area used for reading. It points to membuf if we are
* memory-backed, or it is the mmap view of the file if we are file-backed
*/
const T* readbuf = (const T*)MAP_FAILED;
/// Number of items appended so far
size_t m_count = 0;
/// Unix file descriptor to the temporary file, or -1 if we are memory
/// backed
int tmpfile_fd = -1;
public:
Structbuf()
: membuf(new T[bufsize])
{
}
~Structbuf()
{
delete[] membuf;
if (tmpfile_fd != -1)
{
if (readbuf != MAP_FAILED)
munmap((void*)readbuf, m_count * sizeof(T));
::close(tmpfile_fd);
}
}
/// Get the number of structures that have been added to the buffer so far
size_t size() const { return m_count; }
/// Return true if the buffer has become file-backed
bool is_file_backed() const { return tmpfile_fd != -1; }
/// Append an item to the buffer
void append(const T& val)
{
if (readbuf != MAP_FAILED)
throw wreport::error_consistency("writing to a Structbuf that is already being read");
if (membuf_last == bufsize)
write_to_file();
membuf[membuf_last++] = val;
++m_count;
}
/// Stop appending and get ready to read back the data
void ready_to_read()
{
if (tmpfile_fd == -1)
readbuf = membuf;
else
{
// Flush the remaining memory data to file
if (membuf_last) write_to_file();
// mmap the file for reading
readbuf = (const T*)mmap(nullptr, m_count * sizeof(T), PROT_READ, MAP_SHARED, tmpfile_fd, 0);
if (readbuf == MAP_FAILED)
throw wreport::error_system("cannot map temporary file contents to memory");
}
}
/// Read back an item
const T& operator[](size_t idx) const
{
return readbuf[idx];
}
protected:
void write_to_file()
{
if (tmpfile_fd == -1)
tmpfile_fd = structbuf::make_anonymous_tmpfile();
structbuf::write_buffer(tmpfile_fd, membuf, sizeof(T) * membuf_last);
membuf_last = 0;
}
};
}
#endif
|