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// @file distlock.h
/* Copyright 2009 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "pch.h"
#include "dbclient.h"
#include "distlock.h"
namespace mongo {
LabeledLevel DistributedLock::logLvl( 1 );
DistributedLock::LastPings DistributedLock::lastPings;
ThreadLocalValue<string> distLockIds("");
/* ==================
* Module initialization
*/
boost::once_flag _init = BOOST_ONCE_INIT;
static string* _cachedProcessString = NULL;
static void initModule() {
// cache process string
stringstream ss;
ss << getHostName() << ":" << cmdLine.port << ":" << time(0) << ":" << rand();
_cachedProcessString = new string( ss.str() );
}
/* =================== */
string getDistLockProcess() {
boost::call_once( initModule, _init );
assert( _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;
}
class DistributedLockPinger {
public:
DistributedLockPinger()
: _mutex( "DistributedLockPinger" ) {
}
void _distLockPingThread( ConnectionString addr, string process, unsigned long long sleepTime ) {
setThreadName( "LockPinger" );
string pingId = pingThreadId( addr, process );
log( DistributedLock::logLvl - 1 ) << "creating distributed lock ping thread for " << addr
<< " and process " << process
<< " (sleeping for " << sleepTime << "ms)" << endl;
static int loops = 0;
while( ! inShutdown() && ! shouldKill( addr, process ) ) {
log( DistributedLock::logLvl + 2 ) << "distributed lock pinger '" << pingId << "' about to ping." << endl;
Date_t pingTime;
try {
ScopedDbConnection conn( addr, 30.0 );
pingTime = jsTime();
// refresh the entry corresponding to this process in the lockpings collection
conn->update( DistributedLock::lockPingNS ,
BSON( "_id" << process ) ,
BSON( "$set" << BSON( "ping" << pingTime ) ) ,
true );
string err = conn->getLastError();
if ( ! err.empty() ) {
warning() << "pinging failed for distributed lock pinger '" << pingId << "'."
<< causedBy( err ) << endl;
conn.done();
// Sleep for normal ping time
sleepmillis(sleepTime);
continue;
}
// remove really old entries from the lockpings collection if they're not holding a lock
// (this may happen if an instance of a process was taken down and no new instance came up to
// replace it for a quite a while)
// if the lock is taken, the take-over mechanism should handle the situation
auto_ptr<DBClientCursor> c = conn->query( DistributedLock::locksNS , BSONObj() );
// TODO: Would be good to make clear whether query throws or returns empty on errors
uassert( 16060, str::stream() << "cannot query locks collection on config server " << conn.getHost(), c.get() );
set<string> pids;
while ( c->more() ) {
BSONObj lock = c->next();
if ( ! lock["process"].eoo() ) {
pids.insert( lock["process"].valuestrsafe() );
}
}
Date_t fourDays = pingTime - ( 4 * 86400 * 1000 ); // 4 days
conn->remove( DistributedLock::lockPingNS , BSON( "_id" << BSON( "$nin" << pids ) << "ping" << LT << fourDays ) );
err = conn->getLastError();
if ( ! err.empty() ) {
warning() << "ping cleanup for distributed lock pinger '" << pingId << " failed."
<< causedBy( err ) << endl;
conn.done();
// Sleep for normal ping time
sleepmillis(sleepTime);
continue;
}
// create index so remove is fast even with a lot of servers
if ( loops++ == 0 ) {
conn->ensureIndex( DistributedLock::lockPingNS , BSON( "ping" << 1 ) );
}
log( DistributedLock::logLvl - ( loops % 10 == 0 ? 1 : 0 ) ) << "cluster " << addr << " pinged successfully at " << pingTime
<< " by distributed lock pinger '" << pingId
<< "', sleeping for " << sleepTime << "ms" << endl;
// Remove old locks, if possible
// Make sure no one else is adding to this list at the same time
scoped_lock lk( _mutex );
int numOldLocks = _oldLockOIDs.size();
if( numOldLocks > 0 )
log( DistributedLock::logLvl - 1 ) << "trying to delete " << _oldLockOIDs.size() << " old lock entries for process " << process << endl;
bool removed = false;
for( list<OID>::iterator i = _oldLockOIDs.begin(); i != _oldLockOIDs.end();
i = ( removed ? _oldLockOIDs.erase( i ) : ++i ) ) {
removed = false;
try {
// Got OID from lock with id, so we don't need to specify id again
conn->update( DistributedLock::locksNS ,
BSON( "ts" << *i ),
BSON( "$set" << BSON( "state" << 0 ) ) );
// Either the update went through or it didn't, either way we're done trying to
// unlock
log( DistributedLock::logLvl - 1 ) << "handled late remove of old distributed lock with ts " << *i << endl;
removed = true;
}
catch( UpdateNotTheSame& ) {
log( DistributedLock::logLvl - 1 ) << "partially removed old distributed lock with ts " << *i << endl;
removed = true;
}
catch ( std::exception& e) {
warning() << "could not remove old distributed lock with ts " << *i
<< causedBy( e ) << endl;
}
}
if( numOldLocks > 0 && _oldLockOIDs.size() > 0 ){
log( DistributedLock::logLvl - 1 ) << "not all old lock entries could be removed for process " << process << endl;
}
conn.done();
}
catch ( std::exception& e ) {
warning() << "distributed lock pinger '" << pingId << "' detected an exception while pinging."
<< causedBy( e ) << endl;
}
sleepmillis(sleepTime);
}
warning() << "removing distributed lock ping thread '" << pingId << "'" << endl;
if( shouldKill( addr, process ) )
finishKill( addr, process );
}
void distLockPingThread( ConnectionString addr, long long clockSkew, string processId, unsigned long long sleepTime ) {
try {
jsTimeVirtualThreadSkew( clockSkew );
_distLockPingThread( addr, processId, sleepTime );
}
catch ( std::exception& e ) {
error() << "unexpected error while running distributed lock pinger for " << addr << ", process " << processId << causedBy( e ) << endl;
}
catch ( ... ) {
error() << "unknown error while running distributed lock pinger for " << addr << ", process " << processId << endl;
}
}
string pingThreadId( const ConnectionString& conn, const string& processId ) {
return conn.toString() + "/" + processId;
}
string got( DistributedLock& lock, unsigned long long sleepTime ) {
// Make sure we don't start multiple threads for a process id
scoped_lock lk( _mutex );
const ConnectionString& conn = lock.getRemoteConnection();
const string& processId = lock.getProcessId();
string s = pingThreadId( conn, processId );
// Ignore if we already have a pinging thread for this process.
if ( _seen.count( s ) > 0 ) return s;
// Check our clock skew
try {
if( lock.isRemoteTimeSkewed() ) {
throw LockException( str::stream() << "clock skew of the cluster " << conn.toString() << " is too far out of bounds to allow distributed locking." , 13650 );
}
}
catch( LockException& e) {
throw LockException( str::stream() << "error checking clock skew of cluster " << conn.toString() << causedBy( e ) , 13651);
}
boost::thread t( boost::bind( &DistributedLockPinger::distLockPingThread, this, conn, getJSTimeVirtualThreadSkew(), processId, sleepTime) );
_seen.insert( s );
return s;
}
void addUnlockOID( const OID& oid ) {
// Modifying the lock from some other thread
scoped_lock lk( _mutex );
_oldLockOIDs.push_back( oid );
}
bool willUnlockOID( const OID& oid ) {
scoped_lock lk( _mutex );
return find( _oldLockOIDs.begin(), _oldLockOIDs.end(), oid ) != _oldLockOIDs.end();
}
void kill( const ConnectionString& conn, const string& processId ) {
// Make sure we're in a consistent state before other threads can see us
scoped_lock lk( _mutex );
string pingId = pingThreadId( conn, processId );
assert( _seen.count( pingId ) > 0 );
_kill.insert( pingId );
}
bool shouldKill( const ConnectionString& conn, const string& processId ) {
return _kill.count( pingThreadId( conn, processId ) ) > 0;
}
void finishKill( const ConnectionString& conn, const string& processId ) {
// Make sure we're in a consistent state before other threads can see us
scoped_lock lk( _mutex );
string pingId = pingThreadId( conn, processId );
_kill.erase( pingId );
_seen.erase( pingId );
}
set<string> _kill;
set<string> _seen;
mongo::mutex _mutex;
list<OID> _oldLockOIDs;
} distLockPinger;
const string DistributedLock::lockPingNS = "config.lockpings";
const string DistributedLock::locksNS = "config.locks";
/**
* 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) , _id( BSON( "_id" << name ) ), _processId( asProcess ? getDistLockId() : getDistLockProcess() ),
_lockTimeout( lockTimeout == 0 ? LOCK_TIMEOUT : lockTimeout ), _maxClockSkew( _lockTimeout / LOCK_SKEW_FACTOR ), _maxNetSkew( _maxClockSkew ), _lockPing( _maxClockSkew ),
_mutex( "DistributedLock" )
{
log( logLvl - 1 ) << "created new distributed lock for " << name << " on " << conn
<< " ( lock timeout : " << _lockTimeout
<< ", ping interval : " << _lockPing << ", process : " << asProcess << " )" << endl;
}
DistributedLock::PingData DistributedLock::LastPings::getLastPing( const ConnectionString& conn, const string& lockName ){
scoped_lock lock( _mutex );
return _lastPings[ std::pair< string, string >( conn.toString(), lockName ) ];
}
void DistributedLock::LastPings::setLastPing( const ConnectionString& conn, const string& lockName, const PingData& pd ){
scoped_lock lock( _mutex );
_lastPings[ std::pair< string, string >( conn.toString(), lockName ) ] = pd;
}
Date_t DistributedLock::getRemoteTime() {
return DistributedLock::remoteTime( _conn, _maxNetSkew );
}
bool DistributedLock::isRemoteTimeSkewed() {
return !DistributedLock::checkSkew( _conn, NUM_LOCK_SKEW_CHECKS, _maxClockSkew, _maxNetSkew );
}
const ConnectionString& DistributedLock::getRemoteConnection() {
return _conn;
}
const string& DistributedLock::getProcessId() {
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() );
ScopedDbConnection conn( server );
BSONObj result;
long long delay;
try {
Date_t then = jsTime();
bool success = conn->runCommand( string("admin"), BSON( "serverStatus" << 1 ), result );
delay = jsTime() - then;
if( !success )
throw TimeNotFoundException( str::stream() << "could not get status from server "
<< server.toString() << " in cluster " << cluster.toString()
<< " to check time", 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 > (long long) (maxNetSkew * 2) )
throw TimeNotFoundException( str::stream() << "server " << server.toString()
<< " in cluster " << cluster.toString()
<< " did not respond within max network delay of "
<< maxNetSkew << "ms", 13648 );
}
catch(...) {
conn.done();
throw;
}
conn.done();
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] += (long long) (remote - local);
log( logLvl + 1 ) << "skew from remote server " << server << " found: " << (long long) (remote - local) << endl;
}
}
// 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;
}
// For use in testing, ping thread should run indefinitely in practice.
bool DistributedLock::killPinger( DistributedLock& lock ) {
if( lock._threadId == "") return false;
distLockPinger.kill( lock._conn, lock._processId );
return true;
}
// 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.
// If we are only trying to re-enter a currently held lock, reenter should be true.
// Note: reenter doesn't actually make this lock re-entrant in the normal sense, since it can still only
// be unlocked once, instead it is used to verify that the lock is already held.
bool DistributedLock::lock_try( const string& why , bool reenter, BSONObj * other ) {
// TODO: Start pinging only when we actually get the lock?
// If we don't have a thread pinger, make sure we shouldn't have one
if( _threadId == "" ){
scoped_lock lk( _mutex );
_threadId = distLockPinger.got( *this, _lockPing );
}
// This should always be true, if not, we are using the lock incorrectly.
assert( _name != "" );
// write to dummy if 'other' is null
BSONObj dummyOther;
if ( other == NULL )
other = &dummyOther;
ScopedDbConnection conn( _conn );
BSONObjBuilder queryBuilder;
queryBuilder.appendElements( _id );
queryBuilder.append( "state" , 0 );
{
// make sure its there so we can use simple update logic below
BSONObj o = conn->findOne( locksNS , _id ).getOwned();
// Case 1: No locks
if ( o.isEmpty() ) {
try {
log( logLvl ) << "inserting initial doc in " << locksNS << " for lock " << _name << endl;
conn->insert( locksNS , BSON( "_id" << _name << "state" << 0 << "who" << "" ) );
}
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["state"].numberInt() > 0 ) {
string lockName = o["_id"].String() + string("/") + o["process"].String();
bool canReenter = reenter && o["process"].String() == _processId && ! distLockPinger.willUnlockOID( o["ts"].OID() ) && o["state"].numberInt() == 2;
if( reenter && ! canReenter ) {
log( logLvl - 1 ) << "not re-entering distributed lock " << lockName;
if( o["process"].String() != _processId ) log( logLvl - 1 ) << ", different process " << _processId << endl;
else if( o["state"].numberInt() == 2 ) log( logLvl - 1 ) << ", state not finalized" << endl;
else log( logLvl - 1 ) << ", ts " << o["ts"].OID() << " scheduled for late unlock" << endl;
// reset since we've been bounced by a previous lock not being where we thought it was,
// and should go through full forcing process if required.
// (in theory we should never see a ping here if used correctly)
*other = o; other->getOwned(); conn.done(); resetLastPing();
return false;
}
BSONObj lastPing = conn->findOne( lockPingNS , o["process"].wrap( "_id" ) );
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( "_id" << o["process"].String() << "ping" << (Date_t) 0 );
}
unsigned long long elapsed = 0;
unsigned long long takeover = _lockTimeout;
PingData _lastPingCheck = getLastPing();
log( logLvl ) << "checking last ping for lock '" << lockName << "'" << " against process " << _lastPingCheck.get<0>() << " and ping " << _lastPingCheck.get<1>() << endl;
try {
Date_t remote = remoteTime( _conn );
// 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["state"].numberInt() == 2 && ( _lastPingCheck.get<0>() != lastPing["_id"].String() || _lastPingCheck.get<1>() != lastPing["ping"].Date() );
bool recTSChange = _lastPingCheck.get<3>() != o["ts"].OID();
if( recPingChange || recTSChange ) {
// If the ping has changed since we last checked, mark the current date and time
setLastPing( PingData( lastPing["_id"].String().c_str(), lastPing["ping"].Date(), remote, o["ts"].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(_lastPingCheck.get<2>() >= remote)
elapsed = 0;
else
elapsed = remote - _lastPingCheck.get<2>();
}
}
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 && ! canReenter ) {
log( logLvl ) << "could not force lock '" << lockName << "' because elapsed time " << elapsed << " <= takeover time " << takeover << endl;
*other = o; other->getOwned(); conn.done();
return false;
}
else if( elapsed > takeover && canReenter ) {
log( logLvl - 1 ) << "not re-entering distributed lock " << lockName << "' because elapsed time " << elapsed << " > takeover time " << takeover << endl;
*other = o; other->getOwned(); conn.done();
return false;
}
log( logLvl - 1 ) << ( canReenter ? "re-entering" : "forcing" ) << " lock '" << lockName << "' because "
<< ( canReenter ? "re-entering is allowed, " : "" )
<< "elapsed time " << elapsed << " > takeover time " << takeover << endl;
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
uassert( 14023, str::stream() << "remote time in cluster " << _conn.toString() << " is now skewed, cannot force lock.", !isRemoteTimeSkewed() );
// 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( locksNS , BSON( "_id" << _id["_id"].String() << "state" << o["state"].numberInt() << "ts" << o["ts"] ),
BSON( "$set" << BSON( "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 ) {
( errMsg.empty() ? log( logLvl - 1 ) : warning() ) << "Could not force lock '" << lockName << "' "
<< ( !errMsg.empty() ? causedBy(errMsg) : string("(another force won)") ) << endl;
*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( std::exception& e ) {
conn.done();
throw LockException( str::stream() << "exception forcing distributed lock "
<< lockName << causedBy( e ), 13660);
}
}
else {
assert( canReenter );
// Lock may be re-entered, reset our timer if succeeds or fails
// 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( locksNS , BSON( "_id" << _id["_id"].String() << "state" << 2 << "ts" << o["ts"] ),
BSON( "$set" << BSON( "state" << 2 ) ) );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
// TODO: Clean up all the extra code to exit this method, probably with a refactor
if ( ! errMsg.empty() || ! err["n"].type() || err["n"].numberInt() < 1 ) {
( errMsg.empty() ? log( logLvl - 1 ) : warning() ) << "Could not re-enter lock '" << lockName << "' "
<< ( !errMsg.empty() ? causedBy(errMsg) : string("(not sure lock is held)") )
<< " gle: " << err
<< endl;
*other = o; other->getOwned(); conn.done();
return false;
}
}
catch( UpdateNotTheSame& ) {
// NOT ok to continue since our lock isn't held by all servers, so isn't valid.
warning() << "inconsistent state re-entering lock, lock " << lockName << " not held" << endl;
*other = o; other->getOwned(); conn.done();
return false;
}
catch( std::exception& e ) {
conn.done();
throw LockException( str::stream() << "exception re-entering distributed lock "
<< lockName << causedBy( e ), 13660);
}
log( logLvl - 1 ) << "re-entered distributed lock '" << lockName << "'" << endl;
*other = o; other->getOwned(); conn.done();
return true;
}
log( logLvl - 1 ) << "lock '" << lockName << "' successfully forced" << endl;
// We don't need the ts value in the query, since we will only ever replace locks with state=0.
}
// Case 3: We have an expired lock
else if ( o["ts"].type() ) {
queryBuilder.append( o["ts"] );
}
}
// Always reset our ping if we're trying to get a lock, since getting a lock implies the lock state is open
// and no locks need to be forced. If anything goes wrong, we don't want to remember an old lock.
resetLastPing();
bool gotLock = false;
BSONObj currLock;
BSONObj lockDetails = BSON( "state" << 1 << "who" << getDistLockId() << "process" << _processId <<
"when" << jsTime() << "why" << why << "ts" << OID::gen() );
BSONObj whatIWant = BSON( "$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 << ":\n"
<< lockDetails.jsonString(Strict, true) << "\n"
<< query.jsonString(Strict, true) << endl;
conn->update( locksNS , query , whatIWant );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
currLock = conn->findOne( locksNS , _id );
if ( !errMsg.empty() || !err["n"].type() || err["n"].numberInt() < 1 ) {
( errMsg.empty() ? log( logLvl - 1 ) : warning() ) << "could not acquire lock '" << lockName << "' "
<< ( !errMsg.empty() ? causedBy( errMsg ) : string("(another update won)") ) << endl;
*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( locksNS , _id );
// 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["ts"] < lockDetails["ts"] || indUpdate["state"].numberInt() == 0 ) {
BSONObj grabQuery = BSON( "_id" << _id["_id"].String() << "ts" << indUpdate["ts"].OID() );
// Change ts so we won't be forced, state so we won't be relocked
BSONObj grabChanges = BSON( "ts" << lockDetails["ts"].OID() << "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( locksNS, grabQuery, BSON( "$set" << grabChanges ) );
indUpdate = indDB->findOne( locksNS, _id );
// Our lock should now be set until forcing.
assert( indUpdate["state"].numberInt() == 1 );
}
// 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();
throw LockException( str::stream() << "distributed lock " << lockName
<< " had errors communicating with individual server "
<< up[1].first << causedBy( e ), 13661 );
}
assert( !indUpdate.isEmpty() );
// Find max TS value
if ( currLock.isEmpty() || currLock["ts"] < indUpdate["ts"] ) {
currLock = indUpdate.getOwned();
}
indDB.done();
}
// Locks on all servers are now set and safe until forcing
if ( currLock["ts"] == lockDetails["ts"] ) {
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;
// Register the lock for deletion, to speed up failover
// Not strictly necessary, but helpful
distLockPinger.addUnlockOID( lockDetails["ts"].OID() );
gotLock = false;
}
}
catch( std::exception& e ) {
conn.done();
throw LockException( str::stream() << "exception creating distributed lock "
<< lockName << causedBy( e ), 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() ) == "state" )
finalLockDetails.append( "state", 2 );
else finalLockDetails.append( el );
}
conn->update( locksNS , _id , BSON( "$set" << finalLockDetails.obj() ) );
BSONObj err = conn->getLastErrorDetailed();
string errMsg = DBClientWithCommands::getLastErrorString(err);
currLock = conn->findOne( locksNS , _id );
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();
// Register the bad final lock for deletion, in case it exists
distLockPinger.addUnlockOID( lockDetails["ts"].OID() );
throw LockException( str::stream() << "exception finalizing winning lock"
<< causedBy( e ), 13662 );
}
}
*other = currLock;
other->getOwned();
// Log our lock results
if(gotLock)
log( logLvl - 1 ) << "distributed lock '" << lockName << "' acquired, ts : " << currLock["ts"].OID() << endl;
else
log( logLvl - 1 ) << "distributed lock '" << lockName << "' was not acquired." << endl;
conn.done();
return gotLock;
}
// Unlock now takes an optional pointer to the lock, so you can be specific about which
// particular lock you want to unlock. This is required when the config server is down,
// and so cannot tell you what lock ts you should try later.
void DistributedLock::unlock( BSONObj* oldLockPtr ) {
assert( _name != "" );
string lockName = _name + string("/") + _processId;
const int maxAttempts = 3;
int attempted = 0;
BSONObj oldLock;
if( oldLockPtr ) oldLock = *oldLockPtr;
while ( ++attempted <= maxAttempts ) {
ScopedDbConnection conn( _conn );
try {
if( oldLock.isEmpty() )
oldLock = conn->findOne( locksNS, _id );
if( oldLock["state"].eoo() || oldLock["state"].numberInt() != 2 || oldLock["ts"].eoo() ) {
warning() << "cannot unlock invalid distributed lock " << oldLock << endl;
conn.done();
break;
}
// Use ts when updating lock, so that new locks can be sure they won't get trampled.
conn->update( locksNS ,
BSON( "_id" << _id["_id"].String() << "ts" << oldLock["ts"].OID() ),
BSON( "$set" << BSON( "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( logLvl - 1 ) << "distributed lock '" << lockName << "' unlocked. " << endl;
conn.done();
return;
}
catch( UpdateNotTheSame& ) {
log( logLvl - 1 ) << "distributed lock '" << lockName << "' unlocked (messily). " << endl;
conn.done();
break;
}
catch ( std::exception& e) {
warning() << "distributed lock '" << lockName << "' failed unlock attempt."
<< causedBy( e ) << endl;
conn.done();
// TODO: If our lock timeout is small, sleeping this long may be unsafe.
if( attempted != maxAttempts) sleepsecs(1 << attempted);
}
}
if( attempted > maxAttempts && ! oldLock.isEmpty() && ! oldLock["ts"].eoo() ) {
log( logLvl - 1 ) << "could not unlock distributed lock with ts " << oldLock["ts"].OID()
<< ", will attempt again later" << endl;
// We couldn't unlock the lock at all, so try again later in the pinging thread...
distLockPinger.addUnlockOID( oldLock["ts"].OID() );
}
else if( attempted > maxAttempts ) {
warning() << "could not unlock untracked distributed lock, a manual force may be required" << endl;
}
warning() << "distributed lock '" << lockName << "' couldn't consummate unlock request. "
<< "lock may be taken over after " << ( _lockTimeout / (60 * 1000) )
<< " minutes timeout." << endl;
}
}
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