Represents an ordered collection of file descriptors. This union type either contains: - FDs to be sent on a socket -- with shared ownership, since the sender may still need them, OR - FDs just received, with sole ownership.
Declared in <folly/io/async/fdsock/SocketFds.h>
class SocketFds finalThis hides the variant of containers behind a unique_ptr so that the normal / fast path, which is not passing FDs, is as light as possible, adding just 8 bytes for a pointer.
== Rationale ==
In order to send FDs over Unix sockets, Thrift plumbs them through a variety of classes. Many of these can be used both for send & receive operations (THeader, StreamPayload, etc).
This is especially useful in regular Thrift request-response handler methods, where the same THeader is used for consuming the received FDs, and sending back FDs with the response -- necessarily in that order.
| Name | Description |
|---|---|
Received | File descriptors just received, held with sole ownership. |
SeqNum | Sequence number associating FDs with socket data messages. |
ToSend | File descriptors to be sent on a socket, held with shared ownership. |
| Name | Description |
|---|---|
SocketFds [constructor] | Constructors |
operator= | Move-assigns from another collection, leaving it empty. |
cloneToSendFromOrDfatal | Clones the ToSend file descriptors from another collection. |
dcheckEmpty | Debug-asserts that this collection is empty. |
dcheckReceivedOrEmpty | Debug-asserts that this collection holds Received FDs or is empty. |
dcheckToSendOrEmpty | Debug-asserts that this collection holds ToSend FDs or is empty. |
empty | Returns whether the collection holds no file descriptors. |
getFdSocketSeqNum | Returns the sequence number associated with this collection. |
releaseReceived | Releases and returns the received file descriptors. |
releaseToSendAndSeqNum | Releases the ToSend file descriptors with their sequence number. |
setFdSocketSeqNumOnce | Attaches a sequence number to this collection, at most once. |
size | Returns the number of file descriptors in the collection. |
| Name | Description |
|---|---|
kNoSeqNum | Sentinel sequence number meaning that none was set. |