Question

I have a multithreaded Windows application where one of the threads has a message pump in it. I need to send a message to that thread, passing information to it. However, one of the libraries I want to use in the worker thread requires std::string. Can I do something like the following:

typedef struct tagCOMMAND
{
    std::map<std::string, std::string> locator;
    std::string body;
} COMMAND, *LPCOMMAND;

Then pass the struct to the message like so:

LPCOMMAND cmd;
cmd->body = "Hello";
cmd->locator["Hello"] = "World";
PostThreadMessage(dwThread, MY_CUSTOM_MESSAGE, NULL, (LPARAM)cmd);

If this is okay, who’s responsible for freeing the memory, the calling thread or the worker thread?

N.B. I’m proceeding under the impression that using a Windows message loop is the easiest and best approach here, but I’m not opposed to using something like a Boost library if that’s more appropriate. However, this is an application that is Windows-specific, and will only ever run on Windows, so cross-platform compatibility isn’t something I’m overly concerned with.

Answer 1

It is ok and normal to pass pointer to objects as async message parameters, as long as there is a single receiver (no more and no less).

It should be the responsibility of the receiver to free the memory, since the caller has no indication when it is safe to do it.