merged from gramsrv upstream

internal/store/postgres/blob_storage_lock.go

@@ -0,0 +1,79 @@
+package postgres
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+)
+
+// blobStorageAdvisoryLockKey is the signed int64 encoding of "telesrvb". Every
+// running server holds a shared session lock; the offline migration tool needs
+// the exclusive form, which proves no server using this database is active.
+const blobStorageAdvisoryLockKey int64 = 0x74656c6573727662
+
+type BlobStorageLock struct {
+	conn   *pgx.Conn
+	shared bool
+}
+
+func AcquireBlobRuntimeLock(ctx context.Context, dsn string) (*BlobStorageLock, error) {
+	return acquireBlobStorageLock(ctx, dsn, true)
+}
+
+func AcquireBlobMigrationLock(ctx context.Context, dsn string) (*BlobStorageLock, error) {
+	return acquireBlobStorageLock(ctx, dsn, false)
+}
+
+func acquireBlobStorageLock(ctx context.Context, dsn string, shared bool) (*BlobStorageLock, error) {
+	conn, err := pgx.Connect(ctx, dsn)
+	if err != nil {
+		return nil, fmt.Errorf("connect for blob storage lock: %w", err)
+	}
+	query := "SELECT pg_try_advisory_lock($1)"
+	kind := "exclusive migration"
+	if shared {
+		query = "SELECT pg_try_advisory_lock_shared($1)"
+		kind = "shared runtime"
+	}
+	var acquired bool
+	if err := conn.QueryRow(ctx, query, blobStorageAdvisoryLockKey).Scan(&acquired); err != nil {
+		_ = conn.Close(context.Background())
+		return nil, fmt.Errorf("acquire %s blob storage lock: %w", kind, err)
+	}
+	if !acquired {
+		_ = conn.Close(context.Background())
+		if shared {
+			return nil, fmt.Errorf("blob migration lock is active; wait for the offline migration to finish before starting telesrv")
+		}
+		return nil, fmt.Errorf("one or more telesrv processes are active; stop every process using this PostgreSQL database before migrating blobs")
+	}
+	return &BlobStorageLock{conn: conn, shared: shared}, nil
+}
+
+func (l *BlobStorageLock) Close() error {
+	if l == nil || l.conn == nil {
+		return nil
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	query := "SELECT pg_advisory_unlock($1)"
+	if l.shared {
+		query = "SELECT pg_advisory_unlock_shared($1)"
+	}
+	var unlocked bool
+	err := l.conn.QueryRow(ctx, query, blobStorageAdvisoryLockKey).Scan(&unlocked)
+	closeErr := l.conn.Close(ctx)
+	l.conn = nil
+	if err != nil {
+		return fmt.Errorf("release blob storage lock: %w", err)
+	}
+	if !unlocked {
+		return fmt.Errorf("blob storage advisory lock was not held by its session")
+	}
+	if closeErr != nil {
+		return fmt.Errorf("close blob storage lock connection: %w", closeErr)
+	}
+	return nil
+}