mirror of https://github.com/grpc/grpc.git
Mark D. Roth
7 years ago
commit
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@ -0,0 +1,197 @@ |
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# Transport Explainer |
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|
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@vjpai |
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|
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## Existing Transports |
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|
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[gRPC |
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transports](https://github.com/grpc/grpc/tree/master/src/core/ext/transport) |
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plug in below the core API (one level below the C++ or other wrapped-language |
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API). You can write your transport in C or C++ though; currently (Nov 2017) all |
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the transports are nominally written in C++ though they are idiomatically C. The |
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existing transports are: |
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|
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* [HTTP/2](https://github.com/grpc/grpc/tree/master/src/core/ext/transport/chttp2) |
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* [Cronet](https://github.com/grpc/grpc/tree/master/src/core/ext/transport/cronet) |
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* [In-process](https://github.com/grpc/grpc/tree/master/src/core/ext/transport/inproc) |
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|
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Among these, the in-process is likely the easiest to understand, though arguably |
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also the least similar to a "real" sockets-based transport since it is only used |
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in a single process. |
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|
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## Transport stream ops |
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|
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In the gRPC core implementation, a fundamental struct is the |
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`grpc_transport_stream_op_batch` which represents a collection of stream |
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operations sent to a transport. (Note that in gRPC, _stream_ and _RPC_ are used |
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synonymously since all RPCs are actually streams internally.) The ops in a batch |
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can include: |
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|
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* send\_initial\_metadata |
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- Client: initate an RPC |
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- Server: supply response headers |
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* recv\_initial\_metadata |
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- Client: get response headers |
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- Server: accept an RPC |
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* send\_message (zero or more) : send a data buffer |
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* recv\_message (zero or more) : receive a data buffer |
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* send\_trailing\_metadata |
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- Client: half-close indicating that no more messages will be coming |
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- Server: full-close providing final status for the RPC |
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* recv\_trailing\_metadata: get final status for the RPC |
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- Server extra: This op shouldn't actually be considered complete until the |
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server has also sent trailing metadata to provide the other side with final |
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status |
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* cancel\_stream: Attempt to cancel an RPC |
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* collect\_stats: Get stats |
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|
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The fundamental responsibility of the transport is to transform between this |
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internal format and an actual wire format, so the processing of these operations |
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is largely transport-specific. |
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|
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One or more of these ops are grouped into a batch. Applications can start all of |
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a call's ops in a single batch, or they can split them up into multiple |
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batches. Results of each batch are returned asynchronously via a completion |
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queue. |
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|
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Internally, we use callbacks to indicate completion. The surface layer creates a |
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callback when starting a new batch and sends it down the filter stack along with |
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the batch. The transport must invoke this callback when the batch is complete, |
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and then the surface layer returns an event to the application via the |
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completion queue. Each batch can have up to 3 callbacks: |
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|
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* recv\_initial\_metadata\_ready (called by the transport when the |
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recv\_initial\_metadata op is complete) |
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* recv\_message\_ready (called by the transport when the recv_message op is |
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complete) |
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* on\_complete (called by the transport when the entire batch is complete) |
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|
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## Timelines of transport stream op batches |
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|
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The transport's job is to sequence and interpret various possible interleavings |
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of the basic stream ops. For example, a sample timeline of batches would be: |
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|
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1. Client send\_initial\_metadata: Initiate an RPC with a path (method) and authority |
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1. Server recv\_initial\_metadata: accept an RPC |
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1. Client send\_message: Supply the input proto for the RPC |
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1. Server recv\_message: Get the input proto from the RPC |
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1. Client send\_trailing\_metadata: This is a half-close indicating that the |
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client will not be sending any more messages |
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1. Server recv\_trailing\_metadata: The server sees this from the client and |
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knows that it will not get any more messages. This won't complete yet though, |
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as described above. |
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1. Server send\_initial\_metadata, send\_message, send\_trailing\_metadata: A |
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batch can contain multiple ops, and this batch provides the RPC response |
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headers, response content, and status. Note that sending the trailing |
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metadata will also complete the server's receive of trailing metadata. |
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1. Client recv\_initial\_metadata: The number of ops in one side of the batch |
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has no relation with the number of ops on the other side of the batch. In |
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this case, the client is just collecting the response headers. |
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1. Client recv\_message, recv\_trailing\_metadata: Get the data response and |
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status |
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|
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|
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There are other possible sample timelines. For example, for client-side streaming, a "typical" sequence would be: |
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|
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1. Server: recv\_initial\_metadata |
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- At API-level, that would be the server requesting an RPC |
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1. Server: recv\_trailing\_metadata |
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- This is for when the server wants to know the final completion of the RPC |
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through an `AsyncNotifyWhenDone` API in C++ |
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1. Client: send\_initial\_metadata, recv\_message, recv\_trailing\_metadata |
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- At API-level, that's a client invoking a client-side streaming call. The |
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send\_initial\_metadata is the call invocation, the recv\_message colects |
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the final response from the server, and the recv\_trailing\_metadata gets |
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the `grpc::Status` value that will be returned from the call |
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1. Client: send\_message / Server: recv\_message |
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- Repeat the above step numerous times; these correspond to a client issuing |
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`Write` in a loop and a server doing `Read` in a loop until `Read` fails |
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1. Client: send\_trailing\_metadata / Server: recv\_message that indicates doneness (NULL) |
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- These correspond to a client issuing `WritesDone` which causes the server's |
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`Read` to fail |
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1. Server: send\_message, send\_trailing\_metadata |
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- These correpond to the server doing `Finish` |
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|
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The sends on one side will call their own callbacks when complete, and they will |
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in turn trigger actions that cause the other side's recv operations to |
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complete. In some transports, a send can sometimes complete before the recv on |
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the other side (e.g., in HTTP/2 if there is sufficient flow-control buffer space |
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available) |
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|
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## Other transport duties |
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|
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In addition to these basic stream ops, the transport must handle cancellations |
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of a stream at any time and pass their effects to the other side. For example, |
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in HTTP/2, this triggers a `RST_STREAM` being sent on the wire. The transport |
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must perform operations like pings and statistics that are used to shape |
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transport-level characteristics like flow control (see, for example, their use |
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in the HTTP/2 transport). |
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|
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## Putting things together with detail: Sending Metadata |
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|
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* API layer: `map<string, string>` that is specific to this RPC |
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* Core surface layer: array of `{slice, slice}` pairs where each slice |
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references an underlying string |
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* [Core transport |
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layer](https://github.com/grpc/grpc/tree/master/src/core/lib/transport): list |
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of `{slice, slice}` pairs that includes the above plus possibly some general |
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metadata (e.g., Method and Authority for initial metadata) |
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* [Specific transport |
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layer](https://github.com/grpc/grpc/tree/master/src/core/ext/transport): |
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- Either send it to the other side using transport-specific API (e.g., Cronet) |
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- Or have it sent through the [iomgr/endpoint |
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layer](https://github.com/grpc/grpc/tree/master/src/core/lib/iomgr) (e.g., |
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HTTP/2) |
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- Or just manipulate pointers to get it from one side to the other (e.g., |
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In-process) |
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|
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## Requirements for any transport |
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|
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Each transport implements several operations in a vtbl (may change to actual |
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virtual functions as transport moves to idiomatic C++). |
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|
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The most important and common one is `perform_stream_op`. This function |
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processes a single stream op batch on a specific stream that is associated with |
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a specific transport: |
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|
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* Gets the 6 ops/cancel passed down from the surface |
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* Pass metadata from one side to the other as described above |
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* Transform messages between slice buffer structure and stream of bytes to pass |
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to other side |
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- May require insertion of extra bytes (e.g., per-message headers in HTTP/2) |
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* React to metadata to preserve expected orderings (*) |
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* Schedule invocation of completion callbacks |
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|
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There are other functions in the vtbl as well. |
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|
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* `perform_transport_op` |
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- Configure the transport instance for the connectivity state change notifier |
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or the server-side accept callback |
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- Disconnect transport or set up a goaway for later streams |
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* `init_stream` |
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- Starts a stream from the client-side |
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- (*) Server-side of the transport must call `accept_stream_cb` when a new |
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stream is available |
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* Triggers request-matcher |
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* `destroy_stream`, `destroy_transport` |
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- Free up data related to a stream or transport |
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* `set_pollset`, `set_pollset_set`, `get_endpoint` |
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- Map each specific instance of the transport to FDs being used by iomgr (for |
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HTTP/2) |
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- Get a pointer to the endpoint structure that actually moves the data |
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(wrapper around a socket for HTTP/2) |
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|
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## Book-keeping responsibilities of the transport layer |
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|
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A given transport must keep all of its transport and streams ref-counted. This |
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is essential to make sure that no struct disappears before it is done being |
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used. |
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|
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A transport must also preserve relevant orders for the different categories of |
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ops on a stream, as described above. A transport must also make sure that all |
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relevant batch operations have completed before scheduling the `on_complete` |
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closure for a batch. Further examples include the idea that the server logic |
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expects to not complete recv\_trailing\_metadata until after it actually sends |
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trailing metadata since it would have already found this out by seeing a NULL’ed |
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recv\_message. This is considered part of the transport's duties in preserving |
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orders. |
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@ -1,137 +0,0 @@ |
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/*
|
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* |
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* Copyright 2015 gRPC authors. |
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* |
||||
* Licensed under the Apache License, Version 2.0 (the "License"); |
||||
* you may not use this file except in compliance with the License. |
||||
* You may obtain a copy of the License at |
||||
* |
||||
* http://www.apache.org/licenses/LICENSE-2.0
|
||||
* |
||||
* Unless required by applicable law or agreed to in writing, software |
||||
* distributed under the License is distributed on an "AS IS" BASIS, |
||||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
||||
* See the License for the specific language governing permissions and |
||||
* limitations under the License. |
||||
* |
||||
*/ |
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|
||||
#include "src/core/lib/support/stack_lockfree.h" |
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|
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#include <stdlib.h> |
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#include <string.h> |
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|
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#include <grpc/support/alloc.h> |
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#include <grpc/support/atm.h> |
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#include <grpc/support/log.h> |
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#include <grpc/support/port_platform.h> |
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|
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/* The lockfree node structure is a single architecture-level
|
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word that allows for an atomic CAS to set it up. */ |
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struct lockfree_node_contents { |
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/* next thing to look at. Actual index for head, next index otherwise */ |
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uint16_t index; |
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#ifdef GPR_ARCH_64 |
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uint16_t pad; |
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uint32_t aba_ctr; |
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#else |
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#ifdef GPR_ARCH_32 |
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uint16_t aba_ctr; |
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#else |
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#error Unsupported bit width architecture |
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#endif |
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#endif |
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}; |
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|
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/* Use a union to make sure that these are in the same bits as an atm word */ |
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typedef union lockfree_node { |
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gpr_atm atm; |
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struct lockfree_node_contents contents; |
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} lockfree_node; |
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|
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/* make sure that entries aligned to 8-bytes */ |
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#define ENTRY_ALIGNMENT_BITS 3 |
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/* reserve this entry as invalid */ |
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#define INVALID_ENTRY_INDEX ((1 << 16) - 1) |
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|
||||
struct gpr_stack_lockfree { |
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lockfree_node* entries; |
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lockfree_node head; /* An atomic entry describing curr head */ |
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}; |
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|
||||
gpr_stack_lockfree* gpr_stack_lockfree_create(size_t entries) { |
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gpr_stack_lockfree* stack; |
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stack = (gpr_stack_lockfree*)gpr_malloc(sizeof(*stack)); |
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/* Since we only allocate 16 bits to represent an entry number,
|
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* make sure that we are within the desired range */ |
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/* Reserve the highest entry number as a dummy */ |
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GPR_ASSERT(entries < INVALID_ENTRY_INDEX); |
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stack->entries = (lockfree_node*)gpr_malloc_aligned( |
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entries * sizeof(stack->entries[0]), ENTRY_ALIGNMENT_BITS); |
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/* Clear out all entries */ |
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memset(stack->entries, 0, entries * sizeof(stack->entries[0])); |
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memset(&stack->head, 0, sizeof(stack->head)); |
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|
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GPR_ASSERT(sizeof(stack->entries->atm) == sizeof(stack->entries->contents)); |
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|
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/* Point the head at reserved dummy entry */ |
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stack->head.contents.index = INVALID_ENTRY_INDEX; |
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/* Fill in the pad and aba_ctr to avoid confusing memcheck tools */ |
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#ifdef GPR_ARCH_64 |
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stack->head.contents.pad = 0; |
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#endif |
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stack->head.contents.aba_ctr = 0; |
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return stack; |
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} |
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|
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void gpr_stack_lockfree_destroy(gpr_stack_lockfree* stack) { |
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gpr_free_aligned(stack->entries); |
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gpr_free(stack); |
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} |
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|
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int gpr_stack_lockfree_push(gpr_stack_lockfree* stack, int entry) { |
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lockfree_node head; |
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lockfree_node newhead; |
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lockfree_node curent; |
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lockfree_node newent; |
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|
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/* First fill in the entry's index and aba ctr for new head */ |
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newhead.contents.index = (uint16_t)entry; |
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#ifdef GPR_ARCH_64 |
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/* Fill in the pad to avoid confusing memcheck tools */ |
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newhead.contents.pad = 0; |
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#endif |
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|
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/* Also post-increment the aba_ctr */ |
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curent.atm = gpr_atm_no_barrier_load(&stack->entries[entry].atm); |
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newhead.contents.aba_ctr = ++curent.contents.aba_ctr; |
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gpr_atm_no_barrier_store(&stack->entries[entry].atm, curent.atm); |
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|
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do { |
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/* Atomically get the existing head value for use */ |
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head.atm = gpr_atm_no_barrier_load(&(stack->head.atm)); |
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/* Point to it */ |
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newent.atm = gpr_atm_no_barrier_load(&stack->entries[entry].atm); |
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newent.contents.index = head.contents.index; |
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gpr_atm_no_barrier_store(&stack->entries[entry].atm, newent.atm); |
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} while (!gpr_atm_rel_cas(&(stack->head.atm), head.atm, newhead.atm)); |
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/* Use rel_cas above to make sure that entry index is set properly */ |
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return head.contents.index == INVALID_ENTRY_INDEX; |
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} |
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|
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int gpr_stack_lockfree_pop(gpr_stack_lockfree* stack) { |
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lockfree_node head; |
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lockfree_node newhead; |
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|
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do { |
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head.atm = gpr_atm_acq_load(&(stack->head.atm)); |
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if (head.contents.index == INVALID_ENTRY_INDEX) { |
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return -1; |
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} |
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newhead.atm = |
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gpr_atm_no_barrier_load(&(stack->entries[head.contents.index].atm)); |
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|
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} while (!gpr_atm_no_barrier_cas(&(stack->head.atm), head.atm, newhead.atm)); |
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|
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return head.contents.index; |
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} |
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@ -1,46 +0,0 @@ |
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/*
|
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* |
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* Copyright 2015 gRPC authors. |
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* |
||||
* Licensed under the Apache License, Version 2.0 (the "License"); |
||||
* you may not use this file except in compliance with the License. |
||||
* You may obtain a copy of the License at |
||||
* |
||||
* http://www.apache.org/licenses/LICENSE-2.0
|
||||
* |
||||
* Unless required by applicable law or agreed to in writing, software |
||||
* distributed under the License is distributed on an "AS IS" BASIS, |
||||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
||||
* See the License for the specific language governing permissions and |
||||
* limitations under the License. |
||||
* |
||||
*/ |
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|
||||
#ifndef GRPC_CORE_LIB_SUPPORT_STACK_LOCKFREE_H |
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#define GRPC_CORE_LIB_SUPPORT_STACK_LOCKFREE_H |
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|
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#include <stddef.h> |
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|
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#ifdef __cplusplus |
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extern "C" { |
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#endif |
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|
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typedef struct gpr_stack_lockfree gpr_stack_lockfree; |
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|
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/* This stack must specify the maximum number of entries to track.
|
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The current implementation only allows up to 65534 entries */ |
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gpr_stack_lockfree* gpr_stack_lockfree_create(size_t entries); |
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void gpr_stack_lockfree_destroy(gpr_stack_lockfree* stack); |
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|
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/* Pass in a valid entry number for the next stack entry */ |
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/* Returns 1 if this is the first element on the stack, 0 otherwise */ |
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int gpr_stack_lockfree_push(gpr_stack_lockfree*, int entry); |
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|
||||
/* Returns -1 on empty or the actual entry number */ |
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int gpr_stack_lockfree_pop(gpr_stack_lockfree* stack); |
||||
|
||||
#ifdef __cplusplus |
||||
} |
||||
#endif |
||||
|
||||
#endif /* GRPC_CORE_LIB_SUPPORT_STACK_LOCKFREE_H */ |
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@ -1,7 +1,7 @@ |
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<!-- This file is generated --> |
||||
<Project> |
||||
<PropertyGroup> |
||||
<GrpcCsharpVersion>1.8.0-dev</GrpcCsharpVersion> |
||||
<GrpcCsharpVersion>1.9.0-dev</GrpcCsharpVersion> |
||||
<GoogleProtobufVersion>3.3.0</GoogleProtobufVersion> |
||||
</PropertyGroup> |
||||
</Project> |
||||
|
||||
@ -1,140 +0,0 @@ |
||||
/*
|
||||
* |
||||
* Copyright 2015 gRPC authors. |
||||
* |
||||
* Licensed under the Apache License, Version 2.0 (the "License"); |
||||
* you may not use this file except in compliance with the License. |
||||
* You may obtain a copy of the License at |
||||
* |
||||
* http://www.apache.org/licenses/LICENSE-2.0
|
||||
* |
||||
* Unless required by applicable law or agreed to in writing, software |
||||
* distributed under the License is distributed on an "AS IS" BASIS, |
||||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
||||
* See the License for the specific language governing permissions and |
||||
* limitations under the License. |
||||
* |
||||
*/ |
||||
|
||||
#include "src/core/lib/support/stack_lockfree.h" |
||||
|
||||
#include <stdlib.h> |
||||
|
||||
#include <grpc/support/alloc.h> |
||||
#include <grpc/support/log.h> |
||||
#include <grpc/support/sync.h> |
||||
#include <grpc/support/thd.h> |
||||
#include "test/core/util/test_config.h" |
||||
|
||||
/* max stack size supported */ |
||||
#define MAX_STACK_SIZE 65534 |
||||
|
||||
#define MAX_THREADS 32 |
||||
|
||||
static void test_serial_sized(size_t size) { |
||||
gpr_stack_lockfree* stack = gpr_stack_lockfree_create(size); |
||||
size_t i; |
||||
size_t j; |
||||
|
||||
/* First try popping empty */ |
||||
GPR_ASSERT(gpr_stack_lockfree_pop(stack) == -1); |
||||
|
||||
/* Now add one item and check it */ |
||||
gpr_stack_lockfree_push(stack, 3); |
||||
GPR_ASSERT(gpr_stack_lockfree_pop(stack) == 3); |
||||
GPR_ASSERT(gpr_stack_lockfree_pop(stack) == -1); |
||||
|
||||
/* Now add repeatedly more items and check them */ |
||||
for (i = 1; i < size; i *= 2) { |
||||
for (j = 0; j <= i; j++) { |
||||
GPR_ASSERT(gpr_stack_lockfree_push(stack, (int)j) == (j == 0)); |
||||
} |
||||
for (j = 0; j <= i; j++) { |
||||
GPR_ASSERT(gpr_stack_lockfree_pop(stack) == (int)(i - j)); |
||||
} |
||||
GPR_ASSERT(gpr_stack_lockfree_pop(stack) == -1); |
||||
} |
||||
|
||||
gpr_stack_lockfree_destroy(stack); |
||||
} |
||||
|
||||
static void test_serial() { |
||||
size_t i; |
||||
for (i = 128; i < MAX_STACK_SIZE; i *= 2) { |
||||
test_serial_sized(i); |
||||
} |
||||
test_serial_sized(MAX_STACK_SIZE); |
||||
} |
||||
|
||||
struct test_arg { |
||||
gpr_stack_lockfree* stack; |
||||
int stack_size; |
||||
int nthreads; |
||||
int rank; |
||||
int sum; |
||||
}; |
||||
|
||||
static void test_mt_body(void* v) { |
||||
struct test_arg* arg = (struct test_arg*)v; |
||||
int lo, hi; |
||||
int i; |
||||
int res; |
||||
lo = arg->rank * arg->stack_size / arg->nthreads; |
||||
hi = (arg->rank + 1) * arg->stack_size / arg->nthreads; |
||||
for (i = lo; i < hi; i++) { |
||||
gpr_stack_lockfree_push(arg->stack, i); |
||||
if ((res = gpr_stack_lockfree_pop(arg->stack)) != -1) { |
||||
arg->sum += res; |
||||
} |
||||
} |
||||
while ((res = gpr_stack_lockfree_pop(arg->stack)) != -1) { |
||||
arg->sum += res; |
||||
} |
||||
} |
||||
|
||||
static void test_mt_sized(size_t size, int nth) { |
||||
gpr_stack_lockfree* stack; |
||||
struct test_arg args[MAX_THREADS]; |
||||
gpr_thd_id thds[MAX_THREADS]; |
||||
int sum; |
||||
int i; |
||||
gpr_thd_options options = gpr_thd_options_default(); |
||||
|
||||
stack = gpr_stack_lockfree_create(size); |
||||
for (i = 0; i < nth; i++) { |
||||
args[i].stack = stack; |
||||
args[i].stack_size = (int)size; |
||||
args[i].nthreads = nth; |
||||
args[i].rank = i; |
||||
args[i].sum = 0; |
||||
} |
||||
gpr_thd_options_set_joinable(&options); |
||||
for (i = 0; i < nth; i++) { |
||||
GPR_ASSERT(gpr_thd_new(&thds[i], test_mt_body, &args[i], &options)); |
||||
} |
||||
sum = 0; |
||||
for (i = 0; i < nth; i++) { |
||||
gpr_thd_join(thds[i]); |
||||
sum = sum + args[i].sum; |
||||
} |
||||
GPR_ASSERT((unsigned)sum == ((unsigned)size * (size - 1)) / 2); |
||||
gpr_stack_lockfree_destroy(stack); |
||||
} |
||||
|
||||
static void test_mt() { |
||||
size_t size; |
||||
int nth; |
||||
for (nth = 1; nth < MAX_THREADS; nth++) { |
||||
for (size = 128; size < MAX_STACK_SIZE; size *= 2) { |
||||
test_mt_sized(size, nth); |
||||
} |
||||
test_mt_sized(MAX_STACK_SIZE, nth); |
||||
} |
||||
} |
||||
|
||||
int main(int argc, char** argv) { |
||||
grpc_test_init(argc, argv); |
||||
test_serial(); |
||||
test_mt(); |
||||
return 0; |
||||
} |
||||
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