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//usr/share/doc/db4-devel-4.7.25/examples_cxx/MpoolExample.cpp

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997,2008 Oracle.  All rights reserved.
 *
 * $Id: MpoolExample.cpp,v 12.8 2008/01/08 20:58:26 bostic Exp $
 */

#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <iostream>
#include <fstream>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include <db_cxx.h>

using std::cout;
using std::cerr;
using std::ios;
using std::ofstream;

#define	MPOOL	"mpool"

int init(const char *, int, int);
int run(DB_ENV *, int, int, int);

static int usage();

const char *progname = "MpoolExample";			// Program name.

class MpoolExample : public DbEnv
{
public:
	MpoolExample();
	int initdb(const char *home, int cachesize);
	int run(int hits, int pagesize, int npages);

private:
	static const char FileName[];

// no need for copy and assignment
	MpoolExample(const MpoolExample &);
	void operator = (const MpoolExample &);
};

int main(int argc, char *argv[])
{
	int ret;
	int cachesize = 20 * 1024;
	int hits = 1000;
	int npages = 50;
	int pagesize = 1024;

for (int i = 1; i < argc; ++i) {
		if (strcmp(argv[i], "-c") == 0) {
			if ((cachesize = atoi(argv[++i])) < 20 * 1024)
				usage();
		}
		else if (strcmp(argv[i], "-h") == 0) {
			if ((hits = atoi(argv[++i])) <= 0)
				usage();
		}
		else if (strcmp(argv[i], "-n") == 0) {
			if ((npages = atoi(argv[++i])) <= 0)
				usage();
		}
		else if (strcmp(argv[i], "-p") == 0) {
			if ((pagesize = atoi(argv[++i])) <= 0)
				usage();
		}
		else {
			usage();
		}
	}

// Initialize the file.
	if ((ret = init(MPOOL, pagesize, npages)) != 0)
		return (ret);

try {
		MpoolExample app;

cout << progname
		     << ": cachesize: " << cachesize
		     << "; pagesize: " << pagesize
		     << "; N pages: " << npages << "\n";

if ((ret = app.initdb(NULL, cachesize)) != 0)
			return (ret);
		if ((ret = app.run(hits, pagesize, npages)) != 0)
			return (ret);
		cout << "MpoolExample: completed\n";
		return (EXIT_SUCCESS);
	}
	catch (DbException &dbe) {
		cerr << "MpoolExample: " << dbe.what() << "\n";
		return (EXIT_FAILURE);
	}
}

//
// init --
//	Create a backing file.
//
int
init(const char *file, int pagesize, int npages)
{
	// Create a file with the right number of pages, and store a page
	// number on each page.
	ofstream of(file, ios::out | ios::binary);

if (of.fail()) {
		cerr << "MpoolExample: " << file << ": open failed\n";
		return (EXIT_FAILURE);
	}
	char *p = new char[pagesize];
	memset(p, 0, pagesize);

// The pages are numbered from 0.
	for (int cnt = 0; cnt <= npages; ++cnt) {
		*(db_pgno_t *)p = cnt;
		of.write(p, pagesize);
		if (of.fail()) {
			cerr << "MpoolExample: " << file << ": write failed\n";
			return (EXIT_FAILURE);
		}
	}
	delete [] p;
	return (EXIT_SUCCESS);
}

static int
usage()
{
	cerr << "usage: MpoolExample [-c cachesize] "
	     << "[-h hits] [-n npages] [-p pagesize]\n";
	return (EXIT_FAILURE);
}

// Note: by using DB_CXX_NO_EXCEPTIONS, we get explicit error returns
// from various methods rather than exceptions so we can report more
// information with each error.
//
MpoolExample::MpoolExample()
:	DbEnv(DB_CXX_NO_EXCEPTIONS)
{
}

int MpoolExample::initdb(const char *home, int cachesize)
{
	set_error_stream(&cerr);
	set_errpfx("MpoolExample");
	set_cachesize(0, cachesize, 0);

open(home, DB_CREATE | DB_INIT_MPOOL, 0);
	return (EXIT_SUCCESS);
}

//
// run --
//	Get a set of pages.
//
int
MpoolExample::run(int hits, int pagesize, int npages)
{
	db_pgno_t pageno;
	int cnt, ret;
	void *p;

// Open the file in the environment.
	DbMpoolFile *mfp;

if ((ret = memp_fcreate(&mfp, 0)) != 0) {
		cerr << "MpoolExample: memp_fcreate failed: "
		     << strerror(ret) << "\n";
		return (EXIT_FAILURE);
	}
	mfp->open(MPOOL, 0, 0, pagesize);

cout << "retrieve " << hits << " random pages... ";

srand((unsigned int)time(NULL));
	for (cnt = 0; cnt < hits; ++cnt) {
		pageno = (rand() % npages) + 1;
		if ((ret = mfp->get(&pageno, NULL, 0, &p)) != 0) {
			cerr << "MpoolExample: unable to retrieve page "
			     << (unsigned long)pageno << ": "
			     << strerror(ret) << "\n";
			return (EXIT_FAILURE);
		}
		if (*(db_pgno_t *)p != pageno) {
			cerr << "MpoolExample: wrong page retrieved ("
			     << (unsigned long)pageno << " != "
			     << *(int *)p << ")\n";
			return (EXIT_FAILURE);
		}
		if ((ret = mfp->put(p, DB_PRIORITY_UNCHANGED, 0)) != 0) {
			cerr << "MpoolExample: unable to return page "
			     << (unsigned long)pageno << ": "
			     << strerror(ret) << "\n";
			return (EXIT_FAILURE);
		}
	}

cout << "successful.\n";

// Close the pool.
	if ((ret = close(0)) != 0) {
		cerr << "MpoolExample: " << strerror(ret) << "\n";
		return (EXIT_FAILURE);
	}
	return (EXIT_SUCCESS);
}