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Merge #21007: bitcoind: Add -daemonwait option to wait for initialization

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e017a913d0 bitcoind: Add -daemonwait option to wait for initialization (Wladimir J. van der Laan)
c3e6fdee6d shutdown: Use RAII TokenPipe in shutdown (Wladimir J. van der Laan)
612f746a8f util: Add RAII TokenPipe (Wladimir J. van der Laan)

Pull request description:

  This adds a `-daemonwait` flag that does the same as `-daemon` except that it, from a user perspective, backgrounds the process only after initialization is complete. This is similar to the behaviour of some other software such as c-lightning.

  This can be useful when the process launching bitcoind wants to guarantee that either the RPC server is running, or that initialization failed, before continuing. The exit code indicates the initialization result.

  The use of the libc function `daemon()` is replaced by a custom implementation which is inspired by the [glibc implementation](https://github.com/lattera/glibc/blob/master/misc/daemon.c#L44), but which also creates a pipe from the child to the parent process for communication.

  An additional advantage of having our own `daemon()` implementation is that no MACOS-specific pragmas are needed anymore to silence a deprecation warning.

  TODO:

  - [x] Factor out `token_read` and `token_write` to an utility, and use  them in `shutdown.cpp` as well—this is exactly the same kind of communication mechanism.

      - [x] RAII-ify pipe endpoints.

  - [x] Improve granularity of the `configure.ac` checks. This currently  still checks for the function `daemon()` which makes no sense as  it's not used. It should check for individual functions such as
    `fork()` and `setsid()` etc—the former being required, the second optional.

  - [-] ~~Signal propagation during initialization: if say, pressing Ctrl-C during `-daemonwait` it would be good to pass this SIGINT on to the child process instead of detaching the parent process and letting the child run free.~~ This is not necessary, see https://github.com/bitcoin/bitcoin/pull/21007#issuecomment-769007341.

  Future:

  - Consider if it makes sense to use this in the RPC tests (there would be no more need for "is RPC ready" polling loops). I think this is out of scope for this PR.

ACKs for top commit:
  jonatack:
    Tested ACK e017a913d0 checked change since previous review is move-only

Tree-SHA512: 53369b8ca2247e4cf3af8cb2cfd5b3399e8e0e3296423d64be987004758162a7ddc1287b01a92d7692328edcb2da4cf05d279b1b4ef61a665b71440ab6a6dbe2
This commit is contained in:
Wladimir J. van der Laan
2021-03-11 15:23:24 +01:00
parent e828fc8f52 e017a913d0
commit 92cf3a22e3
9 changed files with 382 additions and 57 deletions
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5
src/init.cpp
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@@ -580,8 +580,9 @@ void SetupServerArgs(NodeContext& node)
argsman.AddArg("-rpcworkqueue=<n>", strprintf("Set the depth of the work queue to service RPC calls (default: %d)", DEFAULT_HTTP_WORKQUEUE), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::RPC);
argsman.AddArg("-server", "Accept command line and JSON-RPC commands", ArgsManager::ALLOW_ANY, OptionsCategory::RPC);
#if HAVE_DECL_DAEMON
argsman.AddArg("-daemon", "Run in the background as a daemon and accept commands", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
#if HAVE_DECL_FORK
argsman.AddArg("-daemon", strprintf("Run in the background as a daemon and accept commands (default: %d)", DEFAULT_DAEMON), ArgsManager::ALLOW_BOOL, OptionsCategory::OPTIONS);
argsman.AddArg("-daemonwait", strprintf("Wait for initialization to be finished before exiting. This implies -daemon (default: %d)", DEFAULT_DAEMONWAIT), ArgsManager::ALLOW_BOOL, OptionsCategory::OPTIONS);
#else
hidden_args.emplace_back("-daemon");
#endif