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// fsync.cpp
#include "pch.h"
#include "mongo/db/d_concurrency.h"
#include "mongo/db/commands.h"
#include "mongo/db/dur.h"
#include "mongo/db/client.h"
#include "mongo/util/background.h"
namespace mongo {
class FSyncLockThread : public BackgroundJob {
void doRealWork();
public:
FSyncLockThread() : BackgroundJob( true ) {}
virtual ~FSyncLockThread(){}
virtual string name() const { return "FSyncLockThread"; }
virtual void run() {
Client::initThread( "fsyncLockWorker" );
try {
doRealWork();
}
catch ( std::exception& e ) {
error() << "FSyncLockThread exception: " << e.what() << endl;
}
cc().shutdown();
}
};
/* see unlockFsync() for unlocking:
db.$cmd.sys.unlock.findOne()
*/
class FSyncCommand : public Command {
public:
static const char* url() { return "http://www.mongodb.org/display/DOCS/fsync+Command"; }
bool locked;
bool pendingUnlock;
SimpleMutex m; // protects locked var above
string err;
boost::condition _threadSync;
boost::condition _unlockSync;
FSyncCommand() : Command( "fsync" ), m("lockfsync") { locked=false; pendingUnlock=false; }
virtual LockType locktype() const { return NONE; }
virtual bool slaveOk() const { return true; }
virtual bool adminOnly() const { return true; }
virtual void help(stringstream& h) const { h << url(); }
virtual bool run(const string& dbname, BSONObj& cmdObj, int, string& errmsg, BSONObjBuilder& result, bool fromRepl) {
if (Lock::isLocked()) {
errmsg = "fsync: Cannot execute fsync command from contexts that hold a data lock";
return false;
}
bool sync = !cmdObj["async"].trueValue(); // async means do an fsync, but return immediately
bool lock = cmdObj["lock"].trueValue();
log() << "CMD fsync: sync:" << sync << " lock:" << lock << endl;
if( lock ) {
if ( ! sync ) {
errmsg = "fsync: sync option must be true when using lock";
return false;
}
SimpleMutex::scoped_lock lk(m);
err = "";
(new FSyncLockThread())->go();
while ( ! locked && err.size() == 0 ) {
_threadSync.wait( m );
}
if ( err.size() ){
errmsg = err;
return false;
}
log() << "db is now locked for snapshotting, no writes allowed. db.fsyncUnlock() to unlock" << endl;
log() << " For more info see " << FSyncCommand::url() << endl;
result.append("info", "now locked against writes, use db.fsyncUnlock() to unlock");
result.append("seeAlso", FSyncCommand::url());
}
else {
// the simple fsync command case
if (sync) {
Lock::GlobalWrite w; // can this be GlobalRead? and if it can, it should be nongreedy.
getDur().commitNow();
}
// question : is it ok this is not in the dblock? i think so but this is a change from past behavior,
// please advise.
result.append( "numFiles" , MemoryMappedFile::flushAll( sync ) );
}
return 1;
}
} fsyncCmd;
SimpleMutex filesLockedFsync("filesLockedFsync");
void FSyncLockThread::doRealWork() {
SimpleMutex::scoped_lock lkf(filesLockedFsync);
Lock::GlobalWrite global(true/*stopGreed*/);
SimpleMutex::scoped_lock lk(fsyncCmd.m);
verify( ! fsyncCmd.locked ); // impossible to get here if locked is true
try {
getDur().syncDataAndTruncateJournal();
}
catch( std::exception& e ) {
error() << "error doing syncDataAndTruncateJournal: " << e.what() << endl;
fsyncCmd.err = e.what();
fsyncCmd._threadSync.notify_one();
fsyncCmd.locked = false;
return;
}
global.downgrade();
try {
MemoryMappedFile::flushAll(true);
}
catch( std::exception& e ) {
error() << "error doing flushAll: " << e.what() << endl;
fsyncCmd.err = e.what();
fsyncCmd._threadSync.notify_one();
fsyncCmd.locked = false;
return;
}
verify( ! fsyncCmd.locked );
fsyncCmd.locked = true;
fsyncCmd._threadSync.notify_one();
while ( ! fsyncCmd.pendingUnlock ) {
fsyncCmd._unlockSync.wait(fsyncCmd.m);
}
fsyncCmd.pendingUnlock = false;
fsyncCmd.locked = false;
fsyncCmd.err = "unlocked";
fsyncCmd._unlockSync.notify_one();
}
bool lockedForWriting() {
return fsyncCmd.locked;
}
// @return true if unlocked
bool _unlockFsync() {
verify(!Lock::isLocked());
SimpleMutex::scoped_lock lk( fsyncCmd.m );
if( !fsyncCmd.locked ) {
return false;
}
fsyncCmd.pendingUnlock = true;
fsyncCmd._unlockSync.notify_one();
fsyncCmd._threadSync.notify_one();
while ( fsyncCmd.locked ) {
fsyncCmd._unlockSync.wait( fsyncCmd.m );
}
return true;
}
}
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