v4, 12 parts[BUG] Unix Builds Requires Pthread Support (was [PATCH v4 00/12] Simple IPC Mechanism)

> On Wed, 17 Feb 2021 21:48:36, Jeff Hostetler wrote:
> 
> >Here is V4 of my "Simple IPC" series. It addresses Gábor's comment WRT
> >shutting down the server to make unit tests more predictable on CI servers.
> >(https://lore.kernel.org/git/20210213093052.GJ1015009@szeder.dev)
> 
> I missed this at the time, but it appears that ipc-unix-socket.c
> forces a dependency on pthreads for Git under Unix-like platforms.
> This is probably not a correct assumption (or likely intended), but
> causes git to no longer build on NonStop x86 and ia64 as of
> 2.32.0-rc0. I am not suggesting undoing this, but amending to make the
> change more sensitive to a lack of pthread support.
> pthread_sigmask() showed up as an undefined external:

> **** ERROR **** [1210]:
>    libgit.a(ipc-unix-socket.o): In function `thread_block_sigpipe':
>    ipc-unix-socket.o(.text+0xb87): unresolved reference to pthread_sigmask.
> 
> On NonStop, pthread_sigmask is defined in -lput or -lspt, which are not used in our build – and would cause a bunch of other issues
> if referenced. The build does define NO_PTHREADS.

> On Mon, May 17, 2021 at 01:46:46PM -0400, Randall S. Becker wrote:
> 
>> On Wed, 17 Feb 2021 21:48:36, Jeff Hostetler wrote:
>>
>>> Here is V4 of my "Simple IPC" series. It addresses Gábor's comment WRT
>>> shutting down the server to make unit tests more predictable on CI servers.
>>> (https://lore.kernel.org/git/20210213093052.GJ1015009@szeder.dev)
>>
>> I missed this at the time, but it appears that ipc-unix-socket.c
>> forces a dependency on pthreads for Git under Unix-like platforms.
>> This is probably not a correct assumption (or likely intended), but
>> causes git to no longer build on NonStop x86 and ia64 as of
>> 2.32.0-rc0. I am not suggesting undoing this, but amending to make the
>> change more sensitive to a lack of pthread support.
>> pthread_sigmask() showed up as an undefined external:
> 
> Hrm. Usually we do not assume that threads are available. For "async"
> stuff via run-command, we allow it to be implemented via fork(), and
> insist that the async process talk back to us only over a pipe
> descriptor (so it works whether it's a thread or a separate process).
> In cases where we use worker threads for performance (like index-pack or
> pack-objects), we just run a single "thread" instead, waiting for it to
> complete.
> 
> In the simple-ipc API, there's an explicit "async" interface. But it's
> not clear to me how rich it expects the communication with the caller to
> be (i.e., whether we could get away with the fork() trick here). Or if
> it would be OK for the threading to remain an implementation detail,
> with one "worker" upon whom we wait for completion.
> 

>> **** ERROR **** [1210]:
>>     libgit.a(ipc-unix-socket.o): In function `thread_block_sigpipe':
>>     ipc-unix-socket.o(.text+0xb87): unresolved reference to pthread_sigmask.
>>
>> On NonStop, pthread_sigmask is defined in -lput or -lspt, which are not used in our build – and would cause a bunch of other issues
>> if referenced. The build does define NO_PTHREADS.
> 
> So yeah, you hit that problem because you only have a
> sort-of-pthreads-ish case. But it seems like a system which truly has no
> pthread support at all and defines NO_PTHREADS to tell us so will have
> much more of its compilation broken (because it's also missing obvious
> bits like pthread_create()).
> 
> We already make simple-ipc compilation conditional on NO_UNIX_SOCKETS. I
> think we could probably just do the same for NO_PTHREADS?
> 
> Something like:
> 
> diff --git a/Makefile b/Makefile
> index 3a2d3c80a8..bd7fe0fc24 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1687,14 +1687,20 @@ ifdef NO_UNIX_SOCKETS
>   else
>   	LIB_OBJS += unix-socket.o
>   	LIB_OBJS += unix-stream-server.o
> +endif
> +
> +# All simple-ipc requires threads, and then individual
> +# mechanisms have their own requirements.
> +ifndef NO_PTHREADS
> +	BASIC_CFLAGS += -DSUPPORTS_SIMPLE_IPC
>   	LIB_OBJS += compat/simple-ipc/ipc-shared.o
> +ifndef NO_UNIX_SOCKETS
>   	LIB_OBJS += compat/simple-ipc/ipc-unix-socket.o
>   endif
> -
>   ifdef USE_WIN32_IPC
> -	LIB_OBJS += compat/simple-ipc/ipc-shared.o
>   	LIB_OBJS += compat/simple-ipc/ipc-win32.o
>   endif
> +endif
>   
>   ifdef NO_ICONV
>   	BASIC_CFLAGS += -DNO_ICONV
> diff --git a/simple-ipc.h b/simple-ipc.h
> index dc3606e30b..0f58be7945 100644
> --- a/simple-ipc.h
> +++ b/simple-ipc.h
> @@ -4,11 +4,6 @@
>   /*
>    * See Documentation/technical/api-simple-ipc.txt
>    */
> -
> -#if defined(GIT_WINDOWS_NATIVE) || !defined(NO_UNIX_SOCKETS)
> -#define SUPPORTS_SIMPLE_IPC
> -#endif
> -
>   #ifdef SUPPORTS_SIMPLE_IPC
>   #include "pkt-line.h"
>   
> 

> > In the simple-ipc API, there's an explicit "async" interface. But it's
> > not clear to me how rich it expects the communication with the caller to
> > be (i.e., whether we could get away with the fork() trick here). Or if
> > it would be OK for the threading to remain an implementation detail,
> > with one "worker" upon whom we wait for completion.
> > 
> 
> TBH I forgot that we still support NO_PTHREAD systems.
> I seem to remember that we got rid of some of the non-pthread
> stub functions at one point, but I'm fuzzy on the details.

> WRT to "simple ipc" (and future "builtin fsmonitor"), it's heavily
> threaded.  There's no point in trying to fake it with forks.
> 
> The server side of simple ipc implements a thread pool.  And
> the builtin fsmonitor will use a thread to monitor FS events
> and that thread pool to respond to clients.  All driven from a
> shared queue of events.
> 
> It would be a major overhaul to do all that without threads
> -- and even that assumes that nonstop has a sufficient file
> system notification mechanism.

> On Tue, May 18, 2021 at 07:21:33AM -0400, Jeff Hostetler wrote:
> 
>>> In the simple-ipc API, there's an explicit "async" interface. But it's
>>> not clear to me how rich it expects the communication with the caller to
>>> be (i.e., whether we could get away with the fork() trick here). Or if
>>> it would be OK for the threading to remain an implementation detail,
>>> with one "worker" upon whom we wait for completion.
>>>
>>
>> TBH I forgot that we still support NO_PTHREAD systems.
>> I seem to remember that we got rid of some of the non-pthread
>> stub functions at one point, but I'm fuzzy on the details.
> 
> You're probably thinking of when we got rid of a bunch of #ifdef code
> paths in index-pack, and replaced it with stubs that turn the pthread
> calls into "do nothing" (so all the ugly stuff is in thread-utils.h
> now). But we still very much support systems that don't handle pthreads
> at all.
> 
>> WRT to "simple ipc" (and future "builtin fsmonitor"), it's heavily
>> threaded.  There's no point in trying to fake it with forks.
>>
>> The server side of simple ipc implements a thread pool.  And
>> the builtin fsmonitor will use a thread to monitor FS events
>> and that thread pool to respond to clients.  All driven from a
>> shared queue of events.
>>
>> It would be a major overhaul to do all that without threads
>> -- and even that assumes that nonstop has a sufficient file
>> system notification mechanism.
> 
> OK, that matches my guess from a brief look at the code. Thanks for
> confirming.
> 
>> So, yes, we should ifdef it out as Peff suggests.
> 
> The patch I sent wasn't really tested beyond confirming that "make
> NO_PTHREADS=1" finished compiling (and that test-tool simple-ipc
> barfed appropriately at runtime).
> 
> Do you want to pick it up from there and produce a polished patch? I
> think we should deal with this prior to the v2.32.0 release (and thanks
> Randall for testing and finding it during the -rc0 period).
> 
> -Peff
> 

>On Mon, May 17, 2021 at 01:46:46PM -0400, Randall S. Becker wrote:
>
>> On Wed, 17 Feb 2021 21:48:36, Jeff Hostetler wrote:
>>
>> >Here is V4 of my "Simple IPC" series. It addresses Gábor's comment
>> >WRT shutting down the server to make unit tests more predictable on CI servers.
>> >(https://lore.kernel.org/git/20210213093052.GJ1015009@szeder.dev)
>>
>> I missed this at the time, but it appears that ipc-unix-socket.c
>> forces a dependency on pthreads for Git under Unix-like platforms.
>> This is probably not a correct assumption (or likely intended), but
>> causes git to no longer build on NonStop x86 and ia64 as of
>> 2.32.0-rc0. I am not suggesting undoing this, but amending to make the
>> change more sensitive to a lack of pthread support.
>> pthread_sigmask() showed up as an undefined external:
>
>Hrm. Usually we do not assume that threads are available. For "async"
>stuff via run-command, we allow it to be implemented via fork(), and insist that the async process talk back to us only over a pipe
>descriptor (so it works whether it's a thread or a separate process).
>In cases where we use worker threads for performance (like index-pack or pack-objects), we just run a single "thread" instead, waiting for
>it to complete.
>
>In the simple-ipc API, there's an explicit "async" interface. But it's not clear to me how rich it expects the communication with the caller to
>be (i.e., whether we could get away with the fork() trick here). Or if it would be OK for the threading to remain an implementation detail,
>with one "worker" upon whom we wait for completion.
>
>> **** ERROR **** [1210]:
>>    libgit.a(ipc-unix-socket.o): In function `thread_block_sigpipe':
>>    ipc-unix-socket.o(.text+0xb87): unresolved reference to pthread_sigmask.
>>
>> On NonStop, pthread_sigmask is defined in -lput or -lspt, which are
>> not used in our build – and would cause a bunch of other issues if referenced. The build does define NO_PTHREADS.
>
>So yeah, you hit that problem because you only have a sort-of-pthreads-ish case. But it seems like a system which truly has no pthread
>support at all and defines NO_PTHREADS to tell us so will have much more of its compilation broken (because it's also missing obvious bits
>like pthread_create()).
>
>We already make simple-ipc compilation conditional on NO_UNIX_SOCKETS. I think we could probably just do the same for
>NO_PTHREADS?
>
>Something like:
>
>diff --git a/Makefile b/Makefile
>index 3a2d3c80a8..bd7fe0fc24 100644
>--- a/Makefile
>+++ b/Makefile
>@@ -1687,14 +1687,20 @@ ifdef NO_UNIX_SOCKETS  else
> 	LIB_OBJS += unix-socket.o
> 	LIB_OBJS += unix-stream-server.o
>+endif
>+
>+# All simple-ipc requires threads, and then individual # mechanisms
>+have their own requirements.
>+ifndef NO_PTHREADS
>+	BASIC_CFLAGS += -DSUPPORTS_SIMPLE_IPC
> 	LIB_OBJS += compat/simple-ipc/ipc-shared.o
>+ifndef NO_UNIX_SOCKETS
> 	LIB_OBJS += compat/simple-ipc/ipc-unix-socket.o
> endif
>-
> ifdef USE_WIN32_IPC
>-	LIB_OBJS += compat/simple-ipc/ipc-shared.o
> 	LIB_OBJS += compat/simple-ipc/ipc-win32.o  endif
>+endif
>
> ifdef NO_ICONV
> 	BASIC_CFLAGS += -DNO_ICONV
>diff --git a/simple-ipc.h b/simple-ipc.h index dc3606e30b..0f58be7945 100644
>--- a/simple-ipc.h
>+++ b/simple-ipc.h
>@@ -4,11 +4,6 @@
> /*
>  * See Documentation/technical/api-simple-ipc.txt
>  */
>-
>-#if defined(GIT_WINDOWS_NATIVE) || !defined(NO_UNIX_SOCKETS) -#define SUPPORTS_SIMPLE_IPC -#endif
>-
> #ifdef SUPPORTS_SIMPLE_IPC
> #include "pkt-line.h"

> >+# All simple-ipc requires threads, and then individual # mechanisms
> >+have their own requirements.
> >+ifndef NO_PTHREADS
> >+	BASIC_CFLAGS += -DSUPPORTS_SIMPLE_IPC
> > 	LIB_OBJS += compat/simple-ipc/ipc-shared.o
> >+ifndef NO_UNIX_SOCKETS
> > 	LIB_OBJS += compat/simple-ipc/ipc-unix-socket.o
> > endif
> >-
> > ifdef USE_WIN32_IPC
> >-	LIB_OBJS += compat/simple-ipc/ipc-shared.o
> > 	LIB_OBJS += compat/simple-ipc/ipc-win32.o  endif
> >+endif
> >
> > ifdef NO_ICONV
> > 	BASIC_CFLAGS += -DNO_ICONV
> >diff --git a/simple-ipc.h b/simple-ipc.h index dc3606e30b..0f58be7945 100644
> >--- a/simple-ipc.h
> >+++ b/simple-ipc.h
> >@@ -4,11 +4,6 @@
> > /*
> >  * See Documentation/technical/api-simple-ipc.txt
> >  */
> >-
> >-#if defined(GIT_WINDOWS_NATIVE) || !defined(NO_UNIX_SOCKETS) -#define SUPPORTS_SIMPLE_IPC -#endif
> >-
> > #ifdef SUPPORTS_SIMPLE_IPC
> > #include "pkt-line.h"
> 
> I'm not sure this is going to work. The platform *does* support UNIX
> sockets (and not disabled) and pthreads, but we have disabled pthreads
> in our build. So in the above, ipc-unix-socket.o will be included at
> the ifndef NO_UNIX_SOCKETS. If NO_PTHREADS, not being pedantic, there
> should be no pthread references, regardless of other considerations.
> Although, at some point, I hope to resolve why pthreads (PUT) is
> having issues in git on the platform but not at this point.