$contacts{$contact} = &share( {} ); 
share( $contacts{$contact}{'a'} ); 
share( $contacts{$contact}{'inc_dnd'} ); 
share( $contacts{$contact}{'lock'} ); 
$contacts{$contact}{'a'} = 1; 
$contacts{$contact}{'inc_dnd'} = &share( {} ); 
$contacts{$contact}{'lock'} = 0;
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In a thread, I try to execute
lock( $contacts{$user_id} );