From: Jeff Hostetler Date: Fri, 17 Sep 2021 19:41:53 GMT Subject: Re: [PATCH 7/7] t/helper/simple-ipc: convert test-simple-ipc to use start_bg_command Message-ID: In-Reply-To: On 9/16/21 1:06 AM, Taylor Blau wrote: > On Wed, Sep 15, 2021 at 08:36:17PM +0000, Jeff Hostetler via GitGitGadget wrote: >> From: Jeff Hostetler >> >> Convert test helper to use `start_bg_command()` when spawning a server >> daemon in the background rather than blocks of platform-specific code. >> >> Signed-off-by: Jeff Hostetler >> --- >> t/helper/test-simple-ipc.c | 193 ++++++++----------------------------- >> 1 file changed, 40 insertions(+), 153 deletions(-) >> >> diff --git a/t/helper/test-simple-ipc.c b/t/helper/test-simple-ipc.c >> index 91345180750..59a950f3b00 100644 >> --- a/t/helper/test-simple-ipc.c >> +++ b/t/helper/test-simple-ipc.c >> @@ -9,6 +9,7 @@ >> #include "parse-options.h" >> #include "thread-utils.h" >> #include "strvec.h" >> +#include "run-command.h" >> >> #ifndef SUPPORTS_SIMPLE_IPC >> int cmd__simple_ipc(int argc, const char **argv) >> @@ -274,178 +275,64 @@ static int daemon__run_server(void) >> return ret; >> } >> >> -#ifndef GIT_WINDOWS_NATIVE >> -/* >> - * This is adapted from `daemonize()`. Use `fork()` to directly create and >> - * run the daemon in a child process. >> - */ >> -static int spawn_server(pid_t *pid) >> -{ >> - struct ipc_server_opts opts = { >> - .nr_threads = cl_args.nr_threads, >> - }; >> +static start_bg_wait_cb bg_wait_cb; > > This whole patch is delightful to read, as the new implementation is so > much cleaner as a result of the earlier work in this series. > > Am I correct in assuming that this is to encourage a compiler error if > bg_wait_cb does not satisfy the type of start_bg_wait_cb? If so, then I > think we are already getting that by trying to pass bg_wait_cb to > start_bg_command(). I use that trick to get the compiler to give me a compiler error at the point of the function declaration. For example, If I add an arg to the function that doesn't match what's in the prototype definition, I get: t/helper/test-simple-ipc.c:280:12: error: conflicting types for 'bg_wait_cb' static int bg_wait_cb(const struct child_process *cp, void *cb_data, int foo) ^ t/helper/test-simple-ipc.c:278:25: note: previous declaration is here static start_bg_wait_cb bg_wait_cb; ^ 1 error generated. Yes, we may get an error when the function pointer is referenced in start_bg_command() or if we're using it to initialize a vtable or something, but those errors are further away from the actual error (and sometimes they can be a little cryptic). Also, it helps document that this function's signature is predefined for a reason. It's a quirky trick I know, but it has served me well over the years. > > E.g., applying this (intentionally broken) diff on top: > > --- 8< --- > > diff --git a/t/helper/test-simple-ipc.c b/t/helper/test-simple-ipc.c > index 59a950f3b0..3aed787206 100644 > --- a/t/helper/test-simple-ipc.c > +++ b/t/helper/test-simple-ipc.c > @@ -275,9 +275,7 @@ static int daemon__run_server(void) > return ret; > } > > -static start_bg_wait_cb bg_wait_cb; > - > -static int bg_wait_cb(void *cb_data, const struct child_process *cp) > +static int bg_wait_cb(const void *cb_data, const struct child_process *cp) > { > int s = ipc_get_active_state(cl_args.path); > > --- >8 --- > > and then compiling still warns of a mismatched type when calling > start_bg_command(). > >> - *pid = fork(); >> - >> - switch (*pid) { >> - case 0: >> - if (setsid() == -1) >> - error_errno(_("setsid failed")); >> - close(0); >> - close(1); >> - close(2); >> - sanitize_stdfds(); >> +static int bg_wait_cb(void *cb_data, const struct child_process *cp) >> +{ >> + int s = ipc_get_active_state(cl_args.path); >> >> - return ipc_server_run(cl_args.path, &opts, test_app_cb, >> - (void*)&my_app_data); >> + switch (s) { >> + case IPC_STATE__LISTENING: >> + /* child is "ready" */ >> + return 0; >> >> - case -1: >> - return error_errno(_("could not spawn daemon in the background")); >> + case IPC_STATE__NOT_LISTENING: >> + case IPC_STATE__PATH_NOT_FOUND: >> + /* give child more time */ >> + return 1; >> >> default: > > I'm always a little hesitant to have default cases when switch over enum > types, since it suppresses the warning when there's a new value of that > type. But we already have a similar default in client__probe_server(). Do all compilers now handle switching over an enum and detect unhandled cases? Once upon a time that wasn't the case IIRC. >... > > Ditto. > > Thanks, > Taylor >