GlobalOperationId.al

codeunit 99999 "My Global State"
{
    SingleInstance = true;

    var
        LastOperationId: Guid;
        AllowSmth: Boolean;

    local procedure UpdateState(CurrentOperationId: Guid)
    begin
        if LastOperationId <> CurrentOperationId then
            ClearState();
    end;

    local procedure ClearState()
    begin
        Clear(LastOperationId);
        AllowSmth := false;
    end;

    [EventSubscriber(...)]
    local procedure BeforePost()
    begin
        LastOperationId := GlobalOperationId;
        AllowSmth := true;
    end;

    // Might not be called if an error occurs.
    [EventSubscriber(...)]
    local procedure AfterPost()
    begin
        ClearState();
    end;

    // Something that normally is not allowed.
    [EventSubscriber(...)]
    local procedure OnBeforeSmth(...)
    begin
        // Suppose an error occured during the posting and OnAfterPost was not called and AllowSmth was stil set to true at this point.
        // We must set AllowSmth to false if this is some different operation.

        // Check if we are already doing some different operation but globals are still not reset.
        UpdateState(GlobalOperationId);

        if not AllowSmth then
            Error('This is only allowed during the posting');
    end;
    
    // Now there is still a problem with this code.
    // If AL code does post -> smth -> post, then smth will be allowed when it shouldn't.
    // It is caller/designer responsibility to ensure that GlobalOperationId will be randomized after the post operation.
    // This could be done by only exposing Post method that handles any errors and creates new GlobalOperationId at the very end.
}