Remote Procedure Call (RPC)

HealthCheckThread is replaced by StartHealthCheck function in socket.cpp, but some of the docs/comments are not modified correspondingly. There are 3 files that HealthCheckThread is involved in:

• test/brpc_socket_unittest.cpp(3 occurrences)
• docs/cn/load_balancing.md(1 occurrence)
• src/brpc/socket.h(1 occurrence)

All sentences with 'HealthCheckThread' should be rewritten to sync with the

默认了异常恢复直接是500状态，空白页。能否让我们来做这个呢

Let's support at least reading "b3" header from a single string, most commonly traceid-spanid-1
It would also be nice to support optionally writing this, especially in message providers or others with constrained environments.

Expected behavior

As discussed on openzipkin/b3-propagation#21 and first implemented here: https://github.com/openzipkin/brave/blob/master/brave/src/main/java/bra

For example, we do not provide these methods.

final GraphQLSchema schema = ...
sb.service("/graphql", GraphqlService.builder()
                                     .schema(schema)
                                     .runtimeWiring(c -> {
                                         final StaticDataFetcher bar = new StaticDataFetcher("bar");
                                         c.