[PATCH] Fix build on macOS

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[PATCH] Fix build on macOS

Tom Tromey-4
PR build/25268 points out that the build fails on macOS, because on
macOS the "pthread_setname_np" function takes a single argument.

This patch fixes the problem, by introducing a new template adapter
function that handles both styles of pthread_setname_np.  This is a
technique I learned from Alexandre Oliva, and avoids the need for a
complicated autoconf check.

This change also meant moving the pthread_setname_np call to the
thread function, because macOS only permits setting the name of the
current thread.  This means that there can be a brief window when gdb
will see the wrong name; but I think this is a minor concern.

Tested by rebuilding on x86-64 Fedora 30, and on macOS High Sierra.
On Linux I also debugged gdb to ensure that the thread names are still
set correctly.

gdb/ChangeLog
2019-12-10  Tom Tromey  <[hidden email]>

        PR build/25268:
        * gdbsupport/thread-pool.c (set_thread_name): New template
        function.
        (thread_pool::set_thread_count): Don't call pthread_setname_np.
        (thread_pool::thread_function): Call set_thread_name.

Change-Id: Id7bf28d99ca27a893a9fc87ebb90b15a9c2a9cb4
---
 gdb/ChangeLog                |  8 ++++++++
 gdb/gdbsupport/thread-pool.c | 31 +++++++++++++++++++++++++++----
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/gdb/gdbsupport/thread-pool.c b/gdb/gdbsupport/thread-pool.c
index d19ae02e3ef..8e24570ee96 100644
--- a/gdb/gdbsupport/thread-pool.c
+++ b/gdb/gdbsupport/thread-pool.c
@@ -36,8 +36,28 @@
 #endif
 
 #ifdef USE_PTHREAD_SETNAME_NP
+
 #include <pthread.h>
-#endif
+
+/* Handle platform discrepancies in pthread_setname_np: macOS uses a
+   single-argument form, while Linux uses a two-argument form.  This
+   wrapper template handles the difference.  */
+
+template<typename R, typename A1, typename A2>
+void
+set_thread_name (R (*set_name) (A1, A2), const char *name)
+{
+  set_name (pthread_self (), name);
+}
+
+template<typename R, typename A1>
+void
+set_thread_name (R (*set_name) (A1), const char *name)
+{
+  set_name (name);
+}
+
+#endif /* USE_PTHREAD_SETNAME_NP */
 
 namespace gdb
 {
@@ -75,9 +95,6 @@ thread_pool::set_thread_count (size_t num_threads)
       for (size_t i = m_thread_count; i < num_threads; ++i)
  {
   std::thread thread (&thread_pool::thread_function, this);
-#ifdef USE_PTHREAD_SETNAME_NP
-  pthread_setname_np (thread.native_handle (), "gdb worker");
-#endif
   thread.detach ();
  }
     }
@@ -115,6 +132,12 @@ thread_pool::post_task (std::function<void ()> func)
 void
 thread_pool::thread_function ()
 {
+#ifdef USE_PTHREAD_SETNAME_NP
+  /* This must be done here, because on macOS one can only set the
+     name of the current thread.  */
+  set_thread_name (pthread_setname_np, "gdb worker");
+#endif
+
   /* Ensure that SIGSEGV is delivered to an alternate signal
      stack.  */
   gdb::alternate_signal_stack signal_stack;
--
2.21.0

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Re: [PATCH] Fix build on macOS

Simon Marchi-4
On 2019-12-10 4:47 p.m., Tom Tromey wrote:

> PR build/25268 points out that the build fails on macOS, because on
> macOS the "pthread_setname_np" function takes a single argument.
>
> This patch fixes the problem, by introducing a new template adapter
> function that handles both styles of pthread_setname_np.  This is a
> technique I learned from Alexandre Oliva, and avoids the need for a
> complicated autoconf check.
>
> This change also meant moving the pthread_setname_np call to the
> thread function, because macOS only permits setting the name of the
> current thread.  This means that there can be a brief window when gdb
> will see the wrong name; but I think this is a minor concern.
>
> Tested by rebuilding on x86-64 Fedora 30, and on macOS High Sierra.
> On Linux I also debugged gdb to ensure that the thread names are still
> set correctly.

I think a version without templates would make it a bit simpler to understand:

void
set_thread_name (int (*set_name) (pthread_t, const char *), const char *name)
{
  set_name (pthread_self (), name);
}

void
set_thread_name (int (*set_name) (const char *), const char *name)
{
  set_name (name);
}

Also, they should probably be static, disabling -Wunused-functions, if necessary,
like in:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blobdiff;f=gdb/gdbsupport/safe-strerror.c;h=9973fa678577c3ff1d9188a6679a0c8cecfd5d26;hp=7425af590f789c1625013c9dc51b505a324ad7fd;hb=cb51113052d534b628c635ac7b86b95fe436d60d;hpb=ab7d13f07027e6232a21448ef51f0a52a96738a9

Simon
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Re: [PATCH] Fix build on macOS

Tom Tromey-4
>>>>> "Simon" == Simon Marchi <[hidden email]> writes:

Simon> I think a version without templates would make it a bit simpler to understand:

Yeah, duh.  I wonder why I thought that was needed.

Fixing this taught me that the macOS man page for pthread_setname_np is
incorrect, in that it says the function returns void, whereas
<pthread.h> declares it returning int.

Here's v2.

Tom

commit 3e82417785ea486a2b683e7d7a0cbda88bca1e9a
Author: Tom Tromey <[hidden email]>
Date:   Tue Dec 10 14:16:19 2019 -0700

    Fix build on macOS
   
    PR build/25268 points out that the build fails on macOS, because on
    macOS the "pthread_setname_np" function takes a single argument.
   
    This patch fixes the problem, by introducing a new adapter function
    that handles both styles of pthread_setname_np.
   
    This change also meant moving the pthread_setname_np call to the
    thread function, because macOS only permits setting the name of the
    current thread.  This means that there can be a brief window when gdb
    will see the wrong name; but I think this is a minor concern.
   
    Tested by rebuilding on x86-64 Fedora 30, and on macOS High Sierra.
    On Linux I also debugged gdb to ensure that the thread names are still
    set correctly.
   
    gdb/ChangeLog
    2019-12-10  Tom Tromey  <[hidden email]>
   
            PR build/25268:
            * gdbsupport/thread-pool.c (set_thread_name): New function.
            (thread_pool::set_thread_count): Don't call pthread_setname_np.
            (thread_pool::thread_function): Call set_thread_name.
   
    Change-Id: Id7bf28d99ca27a893a9fc87ebb90b15a9c2a9cb4

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c4e8109b7c5..223a973ccd1 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2019-12-10  Tom Tromey  <[hidden email]>
+
+ PR build/25268:
+ * gdbsupport/thread-pool.c (set_thread_name): New function.
+ (thread_pool::set_thread_count): Don't call pthread_setname_np.
+ (thread_pool::thread_function): Call set_thread_name.
+
 2019-12-10  Christian Biesinger  <[hidden email]>
 
  * gdbsupport/safe-strerror.c: Supress the unused function warning
diff --git a/gdb/gdbsupport/thread-pool.c b/gdb/gdbsupport/thread-pool.c
index d19ae02e3ef..7c63fc6aa02 100644
--- a/gdb/gdbsupport/thread-pool.c
+++ b/gdb/gdbsupport/thread-pool.c
@@ -25,6 +25,7 @@
 #include "gdbsupport/alt-stack.h"
 #include "gdbsupport/block-signals.h"
 #include <algorithm>
+#include "diagnostics.h"
 
 /* On the off chance that we have the pthread library on a Windows
    host, but std::thread is not using it, avoid calling
@@ -36,8 +37,31 @@
 #endif
 
 #ifdef USE_PTHREAD_SETNAME_NP
+
 #include <pthread.h>
-#endif
+
+DIAGNOSTIC_PUSH
+DIAGNOSTIC_IGNORE_UNUSED_FUNCTION
+
+/* Handle platform discrepancies in pthread_setname_np: macOS uses a
+   single-argument form, while Linux uses a two-argument form.  This
+   wrapper template handles the difference.  */
+
+static void
+set_thread_name (int (*set_name) (pthread_t, const char *), const char *name)
+{
+  set_name (pthread_self (), name);
+}
+
+static void
+set_thread_name (void (*set_name) (const char *), const char *name)
+{
+  set_name (name);
+}
+
+DIAGNOSTIC_POP
+
+#endif /* USE_PTHREAD_SETNAME_NP */
 
 namespace gdb
 {
@@ -75,9 +99,6 @@ thread_pool::set_thread_count (size_t num_threads)
       for (size_t i = m_thread_count; i < num_threads; ++i)
  {
   std::thread thread (&thread_pool::thread_function, this);
-#ifdef USE_PTHREAD_SETNAME_NP
-  pthread_setname_np (thread.native_handle (), "gdb worker");
-#endif
   thread.detach ();
  }
     }
@@ -115,6 +136,12 @@ thread_pool::post_task (std::function<void ()> func)
 void
 thread_pool::thread_function ()
 {
+#ifdef USE_PTHREAD_SETNAME_NP
+  /* This must be done here, because on macOS one can only set the
+     name of the current thread.  */
+  set_thread_name (pthread_setname_np, "gdb worker");
+#endif
+
   /* Ensure that SIGSEGV is delivered to an alternate signal
      stack.  */
   gdb::alternate_signal_stack signal_stack;
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Re: [PATCH] Fix build on macOS

Simon Marchi-4
On 2019-12-11 8:52 a.m., Tom Tromey wrote:

> @@ -36,8 +37,31 @@
>  #endif
>  
>  #ifdef USE_PTHREAD_SETNAME_NP
> +
>  #include <pthread.h>
> -#endif
> +
> +DIAGNOSTIC_PUSH
> +DIAGNOSTIC_IGNORE_UNUSED_FUNCTION
> +
> +/* Handle platform discrepancies in pthread_setname_np: macOS uses a
> +   single-argument form, while Linux uses a two-argument form.  This
> +   wrapper template handles the difference.  */

This comment still mentions "template", you might want to change it?

Otherwise, that LGTM.

Simon

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Re: [PATCH] Fix build on macOS

Kevin Buettner
In reply to this post by Tom Tromey-4
On Tue, 10 Dec 2019 14:47:17 -0700
Tom Tromey <[hidden email]> wrote:

> PR build/25268 points out that the build fails on macOS, because on
> macOS the "pthread_setname_np" function takes a single argument.
>
> This patch fixes the problem, by introducing a new template adapter
> function that handles both styles of pthread_setname_np.  This is a
> technique I learned from Alexandre Oliva, and avoids the need for a
> complicated autoconf check.
>
> This change also meant moving the pthread_setname_np call to the
> thread function, because macOS only permits setting the name of the
> current thread.  This means that there can be a brief window when gdb
> will see the wrong name; but I think this is a minor concern.
>
> Tested by rebuilding on x86-64 Fedora 30, and on macOS High Sierra.
> On Linux I also debugged gdb to ensure that the thread names are still
> set correctly.
>
> gdb/ChangeLog
> 2019-12-10  Tom Tromey  <[hidden email]>
>
> PR build/25268:
> * gdbsupport/thread-pool.c (set_thread_name): New template
> function.
> (thread_pool::set_thread_count): Don't call pthread_setname_np.
> (thread_pool::thread_function): Call set_thread_name.

Did this ever go in?

If not, I think it looks reasonable.

Kevin

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Re: [PATCH] Fix build on macOS

Tom Tromey-4
>>>>> "Kevin" == Kevin Buettner <[hidden email]> writes:

>> gdb/ChangeLog
>> 2019-12-10  Tom Tromey  <[hidden email]>
>>
>> PR build/25268:
>> * gdbsupport/thread-pool.c (set_thread_name): New template
>> function.
>> (thread_pool::set_thread_count): Don't call pthread_setname_np.
>> (thread_pool::thread_function): Call set_thread_name.

Kevin> Did this ever go in?

Kevin> If not, I think it looks reasonable.

Something like it did, and then there was another fix after that.

Tom
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Re: [PATCH] Fix build on macOS

Kevin Buettner
On Fri, 31 Jan 2020 15:43:29 +0100
Tom Tromey <[hidden email]> wrote:

> >>>>> "Kevin" == Kevin Buettner <[hidden email]> writes:  
>
> >> gdb/ChangeLog
> >> 2019-12-10  Tom Tromey  <[hidden email]>
> >>
> >> PR build/25268:
> >> * gdbsupport/thread-pool.c (set_thread_name): New template
> >> function.
> >> (thread_pool::set_thread_count): Don't call pthread_setname_np.
> >> (thread_pool::thread_function): Call set_thread_name.  
>
> Kevin> Did this ever go in?  
>
> Kevin> If not, I think it looks reasonable.  
>
> Something like it did, and then there was another fix after that.

Yeah, I saw that there was a second fix, but I didn't see the template
stuff, which I thought was pretty cool.

Kevin

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Re: [PATCH] Fix build on macOS

Sourceware - gdb-patches mailing list
On Fri, Jan 31, 2020 at 4:02 PM Kevin Buettner <[hidden email]> wrote:

>
> On Fri, 31 Jan 2020 15:43:29 +0100
> Tom Tromey <[hidden email]> wrote:
>
> > >>>>> "Kevin" == Kevin Buettner <[hidden email]> writes:
> >
> > >> gdb/ChangeLog
> > >> 2019-12-10  Tom Tromey  <[hidden email]>
> > >>
> > >> PR build/25268:
> > >> * gdbsupport/thread-pool.c (set_thread_name): New template
> > >> function.
> > >> (thread_pool::set_thread_count): Don't call pthread_setname_np.
> > >> (thread_pool::thread_function): Call set_thread_name.
> >
> > Kevin> Did this ever go in?
> >
> > Kevin> If not, I think it looks reasonable.
> >
> > Something like it did, and then there was another fix after that.
>
> Yeah, I saw that there was a second fix, but I didn't see the template
> stuff, which I thought was pretty cool.

The ultimate solution used function overloads instead of templates,
which seems simpler.

Christian