Delete unused AtomicCommitWriteLock(). (#3383)

## Summary

This PR deletes unused `AtomicCommitWriteLock()` and simplifies code.

## Test Plan

None.

util/db/dbutil.go

@@ -204,12 +204,12 @@ func (db *Accessor) IsSharedCacheConnection() bool {
 // Atomic executes a piece of code with respect to the database atomically.
 // For transactions where readOnly is false, sync determines whether or not to wait for the result.
 func (db *Accessor) Atomic(fn idemFn, extras ...interface{}) (err error) {
-	return db.atomic(fn, nil, extras...)
+	return db.atomic(fn, extras...)
 }
 
 // Atomic executes a piece of code with respect to the database atomically.
 // For transactions where readOnly is false, sync determines whether or not to wait for the result.
-func (db *Accessor) atomic(fn idemFn, commitLocker sync.Locker, extras ...interface{}) (err error) {
+func (db *Accessor) atomic(fn idemFn, extras ...interface{}) (err error) {
 	atomicDeadline := time.Now().Add(time.Second)
 
 	// note that the sql library will drop panics inside an active transaction
@@ -232,29 +232,6 @@ func (db *Accessor) atomic(fn idemFn, commitLocker sync.Locker, extras ...interf
 	var conn *sql.Conn
 	ctx := context.Background()
 
-	commitWriteLockTaken := false
-	if commitLocker != nil && db.IsSharedCacheConnection() {
-		// When we're using in memory database, the sqlite implementation forces us to use a shared cache
-		// mode so that multiple connections ( i.e. read and write ) could share the database instance.
-		// ( it would also create issues between precompiled statements and regular atomic calls, as the former
-		// would generate a connection on the fly).
-		// when using a shared cache, we have to be aware that there are additional locking mechanisms that are
-		// internal to the sqlite. Two of them which play a role here are the sqlite_unlock_notify which
-		// prevents a shared cache locks from returning "database is busy" error and would block instead, and
-		// table level locks, which ensure that at any one time, a single table may have any number of active
-		// read-locks or a single active write lock.
-		// see https://www.sqlite.org/sharedcache.html for more details.
-		// These shared cache constrains are more strict than the WAL based concurrency limitations, which allows
-		// one writer and multiple readers at the same time.
-		// In particular, the shared cache limitation means that since a connection could become a writer, any synchronization
-		// operating that would prevent this operation from completing could result with a deadlock.
-		// This is the reason why for shared cache connections, we'll take the lock before starting the write transaction,
-		// and would keep it along. It will cause a degraded performance when using a shared cache connection
-		// compared to a private cache connection, but would grentee correct locking semantics.
-		commitLocker.Lock()
-		commitWriteLockTaken = true
-	}
-
 	for i := 0; (i == 0) || dbretry(err); i++ {
 		if i > 0 {
 			if i < infoTxRetries {
@@ -271,21 +248,11 @@ func (db *Accessor) atomic(fn idemFn, commitLocker sync.Locker, extras ...interf
 
 	if err != nil {
 		// fail case - unable to create database connection
-		if commitLocker != nil && commitWriteLockTaken {
-			commitLocker.Unlock()
-		}
 		return
 	}
 	defer conn.Close()
 
 	for i := 0; ; i++ {
-		// check if the lock was taken in previous iteration
-		if commitLocker != nil && (!db.IsSharedCacheConnection()) && commitWriteLockTaken {
-			// undo the lock.
-			commitLocker.Unlock()
-			commitWriteLockTaken = false
-		}
-
 		if i > 0 {
 			if i < infoTxRetries {
 				db.getDecoratedLogger(fn, extras).Infof("db.atomic: %d retries (last err: %v)", i, err)
@@ -319,12 +286,6 @@ func (db *Accessor) atomic(fn idemFn, commitLocker sync.Locker, extras ...interf
 			}
 		}
 
-		// if everytyhing went well, take the lock, as we're going to attempt to commit the transaction to database.
-		if commitLocker != nil && (!commitWriteLockTaken) && (!db.IsSharedCacheConnection()) {
-			commitLocker.Lock()
-			commitWriteLockTaken = true
-		}
-
 		err = tx.Commit()
 		if err == nil {
 			// update the deadline, as it might have been updated.
@@ -335,11 +296,6 @@ func (db *Accessor) atomic(fn idemFn, commitLocker sync.Locker, extras ...interf
 		}
 	}
 
-	// if we've errored, make sure to unlock the commitLocker ( if there is any )
-	if err != nil && commitLocker != nil && commitWriteLockTaken {
-		commitLocker.Unlock()
-	}
-
 	if time.Now().After(atomicDeadline) {
 		db.getDecoratedLogger(fn, extras).Warnf("dbatomic: tx surpassed expected deadline by %v", time.Now().Sub(atomicDeadline))
 	}
@@ -362,14 +318,6 @@ func ResetTransactionWarnDeadline(ctx context.Context, tx *sql.Tx, deadline time
 	return
 }
 
-// AtomicCommitWriteLock executes a piece of code with respect to the database atomically.
-// For transactions where readOnly is false, sync determines whether or not to wait for the result.
-// The commitLocker is being taken before the transaction is committed. In case of an error, the lock would get released.
-// on all success cases ( i.e. err = nil ) the lock would be taken. on all the fail cases, the lock would be released
-func (db *Accessor) AtomicCommitWriteLock(fn idemFn, commitLocker sync.Locker, extras ...interface{}) (err error) {
-	return db.atomic(fn, commitLocker, extras...)
-}
-
 // Vacuum perform a full-vacuum on the given database. In order for the vacuum to succeed, the storage needs to have
 // double the amount of the current database size ( roughly ), and we cannot have any other transaction ( either read
 // or write ) being active.