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/* Copyright 2009 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
#include "mongo/platform/basic.h"
#include "mongo/s/catalog/legacy/distlock.h"
#include "mongo/db/server_options.h"
#include "mongo/client/dbclientcursor.h"
#include "mongo/client/connpool.h"
#include "mongo/s/type_locks.h"
#include "mongo/s/type_lockpings.h"
#include "mongo/util/concurrency/thread_name.h"
#include "mongo/util/log.h"
#include "mongo/util/timer.h"
namespace mongo {
using std::endl;
using std::list;
using std::set;
using std::string;
using std::stringstream;
using std::unique_ptr;
using std::vector;
LabeledLevel DistributedLock::logLvl( 1 );
DistributedLock::LastPings DistributedLock::lastPings;
ThreadLocalValue<string> distLockIds("");
/* ==================
* Module initialization
*/
static SimpleMutex _cachedProcessMutex("distlock_initmodule");
static string* _cachedProcessString = NULL;
static void initModule() {
SimpleMutex::scoped_lock lk(_cachedProcessMutex);
if (_cachedProcessString) {
// someone got the lock before us
return;
}
// cache process string
stringstream ss;
ss << getHostName() << ":" << serverGlobalParams.port << ":" << time(0) << ":" << rand();
_cachedProcessString = new string( ss.str() );
}
/* =================== */
string getDistLockProcess() {
if (!_cachedProcessString)
initModule();
verify( _cachedProcessString );
return *_cachedProcessString;
}
string getDistLockId() {
string s = distLockIds.get();
if ( s.empty() ) {
stringstream ss;
ss << getDistLockProcess() << ":" << getThreadName() << ":" << rand();
s = ss.str();
distLockIds.set( s );
}
return s;
}
LockException::LockException(StringData msg, int code): LockException(msg, code, OID()) {
}
LockException::LockException(StringData msg, int code, DistLockHandle lockID):
DBException(msg.toString(), code),
_mustUnlockID(lockID) {
}
DistLockHandle LockException::getMustUnlockID() const {
return _mustUnlockID;
}
/**
* Create a new distributed lock, potentially with a custom sleep and takeover time. If a custom sleep time is
* specified (time between pings)
*/
DistributedLock::DistributedLock( const ConnectionString& conn , const string& name , unsigned long long lockTimeout, bool asProcess )
: _conn(conn), _name(name),
_processId( asProcess ? getDistLockId() : getDistLockProcess() ),
_lockTimeout( lockTimeout == 0 ? LOCK_TIMEOUT : lockTimeout ),
_maxClockSkew( _lockTimeout / LOCK_SKEW_FACTOR ), _maxNetSkew( _maxClockSkew ),
_lockPing( _maxClockSkew )
{
LOG( logLvl ) << "created new distributed lock for " << name << " on " << conn
<< " ( lock timeout : " << _lockTimeout
<< ", ping interval : " << _lockPing << ", process : " << asProcess << " )" << endl;
}
DistLockPingInfo DistributedLock::LastPings::getLastPing(const ConnectionString& conn,
const string& lockName) {
stdx::lock_guard<stdx::mutex> lock(_mutex);
return _lastPings[std::make_pair(conn.toString(), lockName)];
}
void DistributedLock::LastPings::setLastPing(const ConnectionString& conn,
const string& lockName,
const DistLockPingInfo& pd) {
stdx::lock_guard<stdx::mutex> lock(_mutex);
_lastPings[std::make_pair(conn.toString(), lockName)] = pd;
}
Date_t DistributedLock::getRemoteTime() const {
return DistributedLock::remoteTime(_conn, _maxNetSkew);
}
bool DistributedLock::isRemoteTimeSkewed() const {
return !DistributedLock::checkSkew(_conn,
NUM_LOCK_SKEW_CHECKS,
_maxClockSkew,
_maxNetSkew);
}
const ConnectionString& DistributedLock::getRemoteConnection() const {
return _conn;
}
const string& DistributedLock::getProcessId() const {
return _processId;
}
/**
* Returns the remote time as reported by the cluster or server. The maximum difference between the reported time
* and the actual time on the remote server (at the completion of the function) is the maxNetSkew
*/
Date_t DistributedLock::remoteTime( const ConnectionString& cluster, unsigned long long maxNetSkew ) {
ConnectionString server( *cluster.getServers().begin() );
// Get result and delay if successful, errMsg if not
bool success = false;
BSONObj result;
string errMsg;
Milliseconds delay{0};
unique_ptr<ScopedDbConnection> connPtr;
try {
connPtr.reset( new ScopedDbConnection( server.toString() ) );
ScopedDbConnection& conn = *connPtr;
Date_t then = jsTime();
success = conn->runCommand( string( "admin" ), BSON( "serverStatus" << 1 ), result );
delay = jsTime() - then;
if ( !success ) errMsg = result.toString();
conn.done();
}
catch ( const DBException& ex ) {
if ( connPtr && connPtr->get()->isFailed() ) {
// Return to the pool so the pool knows about the failure
connPtr->done();
}
success = false;
errMsg = ex.toString();
}
if( !success ) {
throw TimeNotFoundException( str::stream() << "could not get status from server "
<< server.toString() << " in cluster "
<< cluster.toString() << " to check time"
<< causedBy( errMsg ),
13647 );
}
// Make sure that our delay is not more than 2x our maximum network skew, since this is the max our remote
// time value can be off by if we assume a response in the middle of the delay.
if (delay > Milliseconds(maxNetSkew * 2)) {
throw TimeNotFoundException( str::stream()
<< "server " << server.toString() << " in cluster "
<< cluster.toString()
<< " did not respond within max network delay of "
<< maxNetSkew << "ms",
13648 );
}
return result["localTime"].Date() - (delay / 2);
}
bool DistributedLock::checkSkew( const ConnectionString& cluster, unsigned skewChecks, unsigned long long maxClockSkew, unsigned long long maxNetSkew ) {
vector<HostAndPort> servers = cluster.getServers();
if(servers.size() < 1) return true;
vector<long long> avgSkews;
for(unsigned i = 0; i < skewChecks; i++) {
// Find the average skew for each server
unsigned s = 0;
for(vector<HostAndPort>::iterator si = servers.begin(); si != servers.end(); ++si,s++) {
if(i == 0) avgSkews.push_back(0);
// Could check if this is self, but shouldn't matter since local network connection should be fast.
ConnectionString server( *si );
vector<long long> skew;
BSONObj result;
Date_t remote = remoteTime( server, maxNetSkew );
Date_t local = jsTime();
// Remote time can be delayed by at most MAX_NET_SKEW
// Skew is how much time we'd have to add to local to get to remote
avgSkews[s] += (remote - local).count();
LOG( logLvl + 1 ) << "skew from remote server " << server << " found: "
<< (remote - local).count();
}
}
// Analyze skews
long long serverMaxSkew = 0;
long long serverMinSkew = 0;
for(unsigned s = 0; s < avgSkews.size(); s++) {
long long avgSkew = (avgSkews[s] /= skewChecks);
// Keep track of max and min skews
if(s == 0) {
serverMaxSkew = avgSkew;
serverMinSkew = avgSkew;
}
else {
if(avgSkew > serverMaxSkew)
serverMaxSkew = avgSkew;
if(avgSkew < serverMinSkew)
serverMinSkew = avgSkew;
}
}
long long totalSkew = serverMaxSkew - serverMinSkew;
// Make sure our max skew is not more than our pre-set limit
if(totalSkew > (long long) maxClockSkew) {
LOG( logLvl + 1 ) << "total clock skew of " << totalSkew << "ms for servers " << cluster << " is out of " << maxClockSkew << "ms bounds." << endl;
return false;
}
LOG( logLvl + 1 ) << "total clock skew of " << totalSkew << "ms for servers " << cluster << " is in " << maxClockSkew << "ms bounds." << endl;
return true;
}
Status DistributedLock::checkStatus(double timeout) {
BSONObj lockObj;
try {
ScopedDbConnection conn(_conn.toString(), timeout );
lockObj = conn->findOne( LocksType::ConfigNS,
BSON( LocksType::name(_name) ) ).getOwned();
conn.done();
}
catch ( DBException& e ) {
return e.toStatus();
}
if ( lockObj.isEmpty() ) {
return Status(ErrorCodes::LockFailed,
str::stream() << "no lock for " << _name << " exists in the locks collection");
}
if ( lockObj[LocksType::state()].numberInt() < 2 ) {
return Status(ErrorCodes::LockFailed,
str::stream() << "lock " << _name << " current state is not held ("
<< lockObj[LocksType::state()].numberInt() << ")");
}
if ( lockObj[LocksType::process()].String() != _processId ) {
return Status(ErrorCodes::LockFailed,
str::stream() << "lock " << _name << " is currently being held by "
<< "another process ("
<< lockObj[LocksType::process()].String() << ")");
}
return Status::OK();
}
static void logErrMsgOrWarn(StringData messagePrefix,
StringData lockName,
StringData errMsg,
StringData altErrMsg) {
if (errMsg.empty()) {
LOG(DistributedLock::logLvl - 1) << messagePrefix << " '" << lockName << "' " <<
altErrMsg << std::endl;
}
else {
warning() << messagePrefix << " '" << lockName << "' " << causedBy(errMsg.toString());
}
}
// Semantics of this method are basically that if the lock cannot be acquired, returns false,
// can be retried. If the lock should not be tried again (some unexpected error),
// a LockException is thrown.
bool DistributedLock::lock_try(const string& why, BSONObj* other, double timeout) {
// This should always be true, if not, we are using the lock incorrectly.
verify( _name != "" );
LOG( logLvl ) << "trying to acquire new distributed lock for " << _name << " on " << _conn
<< " ( lock timeout : " << _lockTimeout
<< ", ping interval : " << _lockPing << ", process : " << _processId << " )"
<< endl;
// write to dummy if 'other' is null
BSONObj dummyOther;
if ( other == NULL )
other = &dummyOther;
ScopedDbConnection conn(_conn.toString(), timeout );
BSONObjBuilder queryBuilder;
queryBuilder.append( LocksType::name() , _name );
queryBuilder.append( LocksType::state() , 0 );
{
// make sure its there so we can use simple update logic below
BSONObj o = conn->findOne( LocksType::ConfigNS , BSON( LocksType::name(_name) ) ).getOwned();
// Case 1: No locks
if ( o.isEmpty() ) {
try {
LOG( logLvl ) << "inserting initial doc in " << LocksType::ConfigNS << " for lock " << _name << endl;
conn->insert( LocksType::ConfigNS,
BSON( LocksType::name(_name)
<< LocksType::state(0)
<< LocksType::who("")
<< LocksType::lockID(OID()) ));
}
catch ( UserException& e ) {
warning() << "could not insert initial doc for distributed lock " << _name << causedBy( e ) << endl;
}
}
// Case 2: A set lock that we might be able to force
else if ( o[LocksType::state()].numberInt() > 0 ) {
string lockName = o[LocksType::name()].String() + string("/") + o[LocksType::process()].String();
BSONObj lastPing = conn->findOne( LockpingsType::ConfigNS, o[LocksType::process()].wrap( LockpingsType::process() ) );
if ( lastPing.isEmpty() ) {
LOG( logLvl ) << "empty ping found for process in lock '" << lockName << "'" << endl;
// TODO: Using 0 as a "no time found" value Will fail if dates roll over, but then, so will a lot.
lastPing = BSON( LockpingsType::process(o[LocksType::process()].String()) <<
LockpingsType::ping(Date_t()) );
}
unsigned long long elapsed = 0;
unsigned long long takeover = _lockTimeout;
DistLockPingInfo lastPingEntry = getLastPing();
LOG(logLvl) << "checking last ping for lock '" << lockName
<< "' against process " << lastPingEntry.processId
<< " and ping " << lastPingEntry.lastPing;
try {
Date_t remote = remoteTime( _conn );
auto pingDocProcessId = lastPing[LockpingsType::process()].String();
auto pingDocPingValue = lastPing[LockpingsType::ping()].Date();
// Timeout the elapsed time using comparisons of remote clock
// For non-finalized locks, timeout 15 minutes since last seen (ts)
// For finalized locks, timeout 15 minutes since last ping
bool recPingChange =
o[LocksType::state()].numberInt() == 2 &&
(lastPingEntry.processId != pingDocProcessId ||
lastPingEntry.lastPing != pingDocPingValue);
bool recTSChange = lastPingEntry.lockSessionId != o[LocksType::lockID()].OID();
if (recPingChange || recTSChange) {
// If the ping has changed since we last checked, mark the current date and time
setLastPing(DistLockPingInfo(pingDocProcessId,
pingDocPingValue,
remote,
o[LocksType::lockID()].OID(),
OID()));
}
else {
// GOTCHA! Due to network issues, it is possible that the current time
// is less than the remote time. We *have* to check this here, otherwise
// we overflow and our lock breaks.
if (lastPingEntry.configLocalTime >= remote)
elapsed = 0;
else
elapsed = (remote - lastPingEntry.configLocalTime).count();
}
}
catch( LockException& e ) {
// Remote server cannot be found / is not responsive
warning() << "Could not get remote time from " << _conn << causedBy( e );
// If our config server is having issues, forget all the pings until we can see it again
resetLastPing();
}
if (elapsed <= takeover) {
LOG(1) << "could not force lock '" << lockName
<< "' because elapsed time " << elapsed
<< " <= takeover time " << takeover;
*other = o; other->getOwned(); conn.done();
return false;
}
LOG(0) << "forcing lock '" << lockName
<< "' because elapsed time " << elapsed
<< " > takeover time " << takeover;
if( elapsed > takeover ) {
// Lock may forced, reset our timer if succeeds or fails
// Ensures that another timeout must happen if something borks up here, and resets our pristine
// ping state if acquired.
resetLastPing();
try {
// Check the clock skew again. If we check this before we get a lock
// and after the lock times out, we can be pretty sure the time is
// increasing at the same rate on all servers and therefore our
// timeout is accurate
if (isRemoteTimeSkewed()) {
string msg(str::stream() << "remote time in cluster "
<< _conn.toString()
<< " is now skewed, cannot force lock.");
throw LockException(msg, ErrorCodes::DistributedClockSkewed);
}
// Make sure we break the lock with the correct "ts" (OID) value, otherwise
// we can overwrite a new lock inserted in the meantime.
conn->update( LocksType::ConfigNS,
BSON( LocksType::name(_name) <<
LocksType::state(o[LocksType::state()].numberInt()) <<
LocksType::lockID(o[LocksType::lockID()].OID()) ),
BSON( "$set" << BSON( LocksType::state(0) ) ) );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
// TODO: Clean up all the extra code to exit this method, probably with a refactor
if ( !errMsg.empty() || !err["n"].type() || err["n"].numberInt() < 1 ) {
logErrMsgOrWarn("Could not force lock", lockName, errMsg, "(another force won");
*other = o; other->getOwned(); conn.done();
return false;
}
}
catch( UpdateNotTheSame& ) {
// Ok to continue since we know we forced at least one lock document, and all lock docs
// are required for a lock to be held.
warning() << "lock forcing " << lockName << " inconsistent" << endl;
}
catch (const LockException& ) {
// Let the exception go up and don't repackage the exception.
throw;
}
catch( std::exception& e ) {
conn.done();
string msg(str::stream() << "exception forcing distributed lock "
<< lockName << causedBy(e));
throw LockException(msg, 13660);
}
}
else {
// Not strictly necessary, but helpful for small timeouts where thread
// scheduling is significant. This ensures that two attempts are still
// required for a force if not acquired, and resets our state if we
// are acquired.
resetLastPing();
// Test that the lock is held by trying to update the finalized state of the lock to the same state
// if it does not update or does not update on all servers, we can't re-enter.
try {
// Test the lock with the correct "ts" (OID) value
conn->update( LocksType::ConfigNS,
BSON( LocksType::name(_name) <<
LocksType::state(2) <<
LocksType::lockID(o[LocksType::lockID()].OID()) ),
BSON( "$set" << BSON( LocksType::state(2) ) ) );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
// TODO: Clean up all the extra code to exit this method, probably with a refactor
if ( ! errMsg.empty() || ! err["n"].type() || err["n"].numberInt() < 1 ) {
logErrMsgOrWarn("Could not re-enter lock", lockName, errMsg, "(not sure lock is held");
*other = o; other->getOwned(); conn.done();
return false;
}
}
catch( UpdateNotTheSame& ) {
// NOT ok to continue since our lock isn't held by all servers, so isn't valid.
warning() << "inconsistent state re-entering lock, lock " << lockName << " not held" << endl;
*other = o; other->getOwned(); conn.done();
return false;
}
catch( std::exception& e ) {
conn.done();
string msg(str::stream() << "exception re-entering distributed lock "
<< lockName << causedBy(e));
throw LockException(msg, 13660);
}
LOG( logLvl - 1 ) << "re-entered distributed lock '" << lockName << "'" << endl;
*other = o.getOwned();
conn.done();
return true;
}
LOG( logLvl - 1 ) << "lock '" << lockName << "' successfully forced" << endl;
// We don't need the ts value in the query, since we will only ever replace locks with state=0.
}
// Case 3: We have an expired lock
else if ( o[LocksType::lockID()].type() ) {
queryBuilder.append( o[LocksType::lockID()] );
}
}
// Always reset our ping if we're trying to get a lock, since getting a lock implies the lock state is open
// and no locks need to be forced. If anything goes wrong, we don't want to remember an old lock.
resetLastPing();
bool gotLock = false;
BSONObj currLock;
BSONObj lockDetails = BSON( LocksType::state(1)
<< LocksType::who(getDistLockId())
<< LocksType::process(_processId)
<< LocksType::when(jsTime())
<< LocksType::why(why)
<< LocksType::lockID(OID::gen()) );
BSONObj whatIWant = BSON( "$set" << lockDetails );
BSONObj query = queryBuilder.obj();
string lockName = _name + string("/") + _processId;
try {
// Main codepath to acquire lock
LOG( logLvl ) << "about to acquire distributed lock '" << lockName << "'";
LOG( logLvl + 1 ) << "trying to acquire lock " << query.toString( false, true )
<< " with details " << lockDetails.toString( false, true ) << endl;
conn->update( LocksType::ConfigNS , query , whatIWant );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
currLock = conn->findOne( LocksType::ConfigNS , BSON( LocksType::name(_name) ) );
if ( !errMsg.empty() || !err["n"].type() || err["n"].numberInt() < 1 ) {
logErrMsgOrWarn("could not acquire lock", lockName, errMsg, "(another update won)");
*other = currLock;
other->getOwned();
gotLock = false;
}
else {
gotLock = true;
}
}
catch ( UpdateNotTheSame& up ) {
// this means our update got through on some, but not others
warning() << "distributed lock '" << lockName << " did not propagate properly." << causedBy( up ) << endl;
// Overall protection derives from:
// All unlocking updates use the ts value when setting state to 0
// This ensures that during locking, we can override all smaller ts locks with
// our own safe ts value and not be unlocked afterward.
for ( unsigned i = 0; i < up.size(); i++ ) {
ScopedDbConnection indDB(up[i].first);
BSONObj indUpdate;
try {
indUpdate = indDB->findOne( LocksType::ConfigNS , BSON( LocksType::name(_name) ) );
// If we override this lock in any way, grab and protect it.
// We assume/ensure that if a process does not have all lock documents, it is no longer
// holding the lock.
// Note - finalized locks may compete too, but we know they've won already if competing
// in this round. Cleanup of crashes during finalizing may take a few tries.
if( indUpdate[LocksType::lockID()] < lockDetails[LocksType::lockID()] || indUpdate[LocksType::state()].numberInt() == 0 ) {
BSONObj grabQuery = BSON( LocksType::name(_name)
<< LocksType::lockID(indUpdate[LocksType::lockID()].OID()) );
// Change ts so we won't be forced, state so we won't be relocked
BSONObj grabChanges = BSON( LocksType::lockID(lockDetails[LocksType::lockID()].OID())
<< LocksType::state(1) );
// Either our update will succeed, and we'll grab the lock, or it will fail b/c some other
// process grabbed the lock (which will change the ts), but the lock will be set until forcing
indDB->update( LocksType::ConfigNS, grabQuery, BSON( "$set" << grabChanges ) );
indUpdate = indDB->findOne( LocksType::ConfigNS, BSON( LocksType::name(_name) ) );
// The tournament was interfered and it is not safe to proceed further.
// One case this could happen is when the LockPinger processes old
// entries from addUnlockOID. See SERVER-10688 for more detailed
// description of race.
if ( indUpdate[LocksType::state()].numberInt() <= 0 ) {
LOG( logLvl - 1 ) << "lock tournament interrupted, "
<< "so no lock was taken; "
<< "new state of lock: " << indUpdate << endl;
// We now break and set our currLock lockID value to zero, so that
// we know that we did not acquire the lock below. Later code will
// cleanup failed entries.
currLock = BSON(LocksType::lockID(OID()));
indDB.done();
break;
}
}
// else our lock is the same, in which case we're safe, or it's a bigger lock,
// in which case we won't need to protect anything since we won't have the lock.
}
catch( std::exception& e ) {
conn.done();
string msg(str::stream() << "distributed lock " << lockName
<< " had errors communicating with individual server "
<< up[1].first << causedBy(e));
throw LockException(msg, 13661);
}
verify( !indUpdate.isEmpty() );
// Find max TS value
if ( currLock.isEmpty() || currLock[LocksType::lockID()] < indUpdate[LocksType::lockID()] ) {
currLock = indUpdate.getOwned();
}
indDB.done();
}
// Locks on all servers are now set and safe until forcing
if ( currLock[LocksType::lockID()] == lockDetails[LocksType::lockID()] ) {
LOG( logLvl - 1 ) << "lock update won, completing lock propagation for '" << lockName << "'" << endl;
gotLock = true;
}
else {
LOG( logLvl - 1 ) << "lock update lost, lock '" << lockName << "' not propagated." << endl;
gotLock = false;
}
}
catch( std::exception& e ) {
conn.done();
string msg(str::stream() << "exception creating distributed lock "
<< lockName << causedBy(e));
throw LockException(msg, 13663 );
}
// Complete lock propagation
if( gotLock ) {
// This is now safe, since we know that no new locks will be placed on top of the ones we've checked for at
// least 15 minutes. Sets the state = 2, so that future clients can determine that the lock is truly set.
// The invariant for rollbacks is that we will never force locks with state = 2 and active pings, since that
// indicates the lock is active, but this means the process creating/destroying them must explicitly poll
// when something goes wrong.
try {
BSONObjBuilder finalLockDetails;
BSONObjIterator bi( lockDetails );
while( bi.more() ) {
BSONElement el = bi.next();
if( (string) ( el.fieldName() ) == LocksType::state() )
finalLockDetails.append( LocksType::state(), 2 );
else finalLockDetails.append( el );
}
conn->update( LocksType::ConfigNS , BSON( LocksType::name(_name) ) , BSON( "$set" << finalLockDetails.obj() ) );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
currLock = conn->findOne( LocksType::ConfigNS , BSON( LocksType::name(_name) ) );
if ( !errMsg.empty() || !err["n"].type() || err["n"].numberInt() < 1 ) {
warning() << "could not finalize winning lock " << lockName
<< ( !errMsg.empty() ? causedBy( errMsg ) : " (did not update lock) " ) << endl;
gotLock = false;
}
else {
// SUCCESS!
gotLock = true;
}
}
catch( std::exception& e ) {
conn.done();
string msg(str::stream() << "exception finalizing winning lock" << causedBy(e));
// Inform caller about the potential orphan lock.
throw LockException(msg,
13662,
lockDetails[LocksType::lockID()].OID());
}
}
*other = currLock;
other->getOwned();
// Log our lock results
if(gotLock)
LOG( logLvl - 1 ) << "distributed lock '" << lockName <<
"' acquired, ts : " << currLock[LocksType::lockID()].OID() << endl;
else
LOG( logLvl - 1 ) << "distributed lock '" << lockName << "' was not acquired." << endl;
conn.done();
return gotLock;
}
// This function *must not* throw exceptions, since it can be used in destructors - failure
// results in queuing and trying again later.
bool DistributedLock::unlock(const DistLockHandle& lockID) {
verify(_name != "");
string lockName = _name + string("/") + _processId;
const int maxAttempts = 3;
int attempted = 0;
while ( ++attempted <= maxAttempts ) {
// Awkward, but necessary since the constructor itself throws exceptions
unique_ptr<ScopedDbConnection> connPtr;
try {
connPtr.reset( new ScopedDbConnection( _conn.toString() ) );
ScopedDbConnection& conn = *connPtr;
// Use ts when updating lock, so that new locks can be sure they won't get trampled.
conn->update(LocksType::ConfigNS,
BSON(LocksType::name(_name)
<< LocksType::lockID(lockID)),
BSON("$set" << BSON(LocksType::state(0))));
// Check that the lock was actually unlocked... if not, try again
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
if ( !errMsg.empty() || !err["n"].type() || err["n"].numberInt() < 1 ){
warning() << "distributed lock unlock update failed, retrying "
<< ( errMsg.empty() ? causedBy( "( update not registered )" ) : causedBy( errMsg ) ) << endl;
conn.done();
continue;
}
LOG(0) << "distributed lock '" << lockName << "' unlocked. ";
conn.done();
return true;
}
catch (const UpdateNotTheSame&) {
LOG(0) << "distributed lock '" << lockName << "' unlocked (messily). ";
// This isn't a connection problem, so don't throw away the conn
connPtr->done();
return true;
}
catch ( std::exception& e) {
warning() << "distributed lock '" << lockName << "' failed unlock attempt."
<< causedBy( e ) << endl;
// TODO: If our lock timeout is small, sleeping this long may be unsafe.
if( attempted != maxAttempts) sleepsecs(1 << attempted);
}
}
return false;
}
}
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