Re: [PATCH 7/7] t/helper/simple-ipc: convert test-simple-ipc to use start_bg_command

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:

quoted

From: Jeff Hostetler <redacted>

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 <redacted>
---
  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.
	

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