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Code Editor : LockExample.cpp

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997,2008 Oracle.  All rights reserved.
 *
 * $Id: LockExample.cpp,v 12.6 2008/01/08 20:58:26 bostic Exp $
 */

#include <sys/types.h>

#include <errno.h>
#include <iostream>
#include <stdlib.h>
#include <string.h>

#include <db_cxx.h>

using std::cin;
using std::cout;
using std::cerr;

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

//
// An example of a program using DBLock and related classes.
//
class LockExample : public DbEnv
{
public:
	void run();
	int error_code() { return (ecode); }

LockExample(const char *home, u_int32_t maxlocks, int do_unlink);

private:
	static const char FileName[];
	int ecode;

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

static int usage();          // forward

int
main(int argc, char *argv[])
{
	const char *home;
	int do_unlink;
	u_int32_t maxlocks;
	int i;

home = "TESTDIR";
	maxlocks = 0;
	do_unlink = 0;
	for (int argnum = 1; argnum < argc; ++argnum) {
		if (strcmp(argv[argnum], "-h") == 0) {
			if (++argnum >= argc)
				return (usage());
			home = argv[argnum];
		}
		else if (strcmp(argv[argnum], "-m") == 0) {
			if (++argnum >= argc)
				return (usage());
			if ((i = atoi(argv[argnum])) <= 0)
				return (usage());
			maxlocks = (u_int32_t)i;  /* XXX: possible overflow. */
		}
		else if (strcmp(argv[argnum], "-u") == 0) {
			do_unlink = 1;
		}
		else {
			return (usage());
		}
	}

try {
		int ecode;

if (do_unlink) {
			// Create an environment that immediately
			// removes all files.
			LockExample tmp(home, maxlocks, do_unlink);
			if ((ecode = tmp.error_code()) != 0)
				return (ecode);
		}

LockExample app(home, maxlocks, do_unlink);
		if ((ecode = app.error_code()) != 0)
			return (ecode);
		app.run();
		app.close(0);
		return (EXIT_SUCCESS);
	}
	catch (DbException &dbe) {
		cerr << "LockExample: " << dbe.what() << "\n";
		return (EXIT_FAILURE);
	}
}

LockExample::LockExample(const char *home, u_int32_t maxlocks, int do_unlink)
:	DbEnv(0)
,	ecode(0)
{
	int ret;

if (do_unlink) {
		if ((ret = remove(home, DB_FORCE)) != 0) {
			cerr << progname << ": DbEnv::remove: "
			     << strerror(errno) << "\n";
			ecode = EXIT_FAILURE;
		}
	}
	else {
		set_error_stream(&cerr);
		set_errpfx("LockExample");
		if (maxlocks != 0)
			set_lk_max_locks(maxlocks);
		open(home, DB_CREATE | DB_INIT_LOCK, 0);
	}
}

void LockExample::run()
{
	long held;
	size_t len;
	u_int32_t locker;
	int did_get, ret;
	DbLock *locks = 0;
	int lockcount = 0;
	int lockid = 0;
	char objbuf[1024];

//
	// Accept lock requests.
	//
	lock_id(&locker);
	for (held = 0;;) {
		cout << "Operation get/release [get]> ";
		cout.flush();

char opbuf[16];
		cin.getline(opbuf, sizeof(opbuf));
		if (cin.eof())
			break;
		if ((len = strlen(opbuf)) <= 1 || strcmp(opbuf, "get") == 0) {
			// Acquire a lock.
			cout << "input object (text string) to lock> ";
			cout.flush();
			cin.getline(objbuf, sizeof(objbuf));
			if (cin.eof())
				break;
			if ((len = strlen(objbuf)) <= 0)
				continue;

char lockbuf[16];
			do {
				cout << "lock type read/write [read]> ";
				cout.flush();
				cin.getline(lockbuf, sizeof(lockbuf));
				if (cin.eof())
					break;
				len = strlen(lockbuf);
			} while (len >= 1 &&
				 strcmp(lockbuf, "read") != 0 &&
				 strcmp(lockbuf, "write") != 0);

db_lockmode_t lock_type;
			if (len <= 1 || strcmp(lockbuf, "read") == 0)
				lock_type = DB_LOCK_READ;
			else
				lock_type = DB_LOCK_WRITE;

Dbt dbt(objbuf, (u_int32_t)strlen(objbuf));

DbLock lock;
			ret = lock_get(locker, DB_LOCK_NOWAIT, &dbt,
				       lock_type, &lock);
			did_get = 1;
			lockid = lockcount++;
			if (locks == NULL) {
				locks = new DbLock[1];
			}
			else {
				DbLock *newlocks = new DbLock[lockcount];
				for (int lockno = 0;
				    lockno < lockid; lockno++) {
					newlocks[lockno] = locks[lockno];
				}
				delete locks;
				locks = newlocks;
			}
			locks[lockid] = lock;
		} else {
			// Release a lock.
			do {
				cout << "input lock to release> ";
				cout.flush();
				cin.getline(objbuf, sizeof(objbuf));
				if (cin.eof())
					break;
			} while ((len = strlen(objbuf)) <= 0);
			lockid = strtol(objbuf, NULL, 16);
			if (lockid < 0 || lockid >= lockcount) {
				cout << "Lock #" << lockid << " out of range\n";
				continue;
			}
			DbLock lock = locks[lockid];
			ret = lock_put(&lock);
			did_get = 0;
		}

switch (ret) {
		case 0:
			cout << "Lock #" << lockid << " "
			     <<  (did_get ? "granted" : "released")
			     << "\n";
			held += did_get ? 1 : -1;
			break;
		case DB_LOCK_NOTGRANTED:
			cout << "Lock not granted\n";
			break;
		case DB_LOCK_DEADLOCK:
			cerr << "LockExample: lock_"
			     << (did_get ? "get" : "put")
			     << ": " << "returned DEADLOCK";
			break;
		default:
			cerr << "LockExample: lock_get: %s",
				strerror(errno);
		}
	}
	cout << "\n";
	cout << "Closing lock region " << held << " locks held\n";
	if (locks != 0)
		delete locks;
}

static int
usage()
{
	cerr << "usage: LockExample [-u] [-h home] [-m maxlocks]\n";
	return (EXIT_FAILURE);
}

${this.title}

Code Editor : LockExample.cpp