fragmented_message.h File Reference

Helper utility for reconstructing large ActiveMessages that were split into multiple network packets. More...

#include "realm/realm_config.h"
#include <vector>
#include <cstdint>
#include <cstring>

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Classes
class	Realm::FragmentedMessage

Namespaces
namespace	Realm

Detailed Description

Helper utility for reconstructing large ActiveMessages that were split into multiple network packets.

Realm (and the underlying network transports such as GASNet-EX or UCX) may have an upper bound on the size of a single medium or long active message. When an application attempts to send a payload larger than that limit, the FragmentedActiveMessage helper in activemsg.h automatically chops the data into N smaller packets. On the receiver side those packets must be collected and concatenated before the logical AM handler can be invoked.

The FragmentedMessage class performs exactly that role: – The sender embeds a small FragmentInfo structure in every fragment that conveys a 0-based chunk_id, the total number of chunks, and a unique msg_id. – The receiver creates one FragmentedMessage instance (looked up by the <sender, msg_id> pair) and calls add_chunk() each time a fragment arrives. – When all total_chunks pieces have been delivered, is_complete() returns true and the caller can safely call reassemble() to obtain a contiguous std::vector<char> containing the payload in order.

A few design notes: • Duplicate fragments are ignored, allowing simple resend logic on the transmit path. • No per-fragment dynamic allocations are performed – each chunk's storage is reserved exactly once when its size becomes known.