[PATCH 2/2] [gdb] Exclude unavailable hardware threads in default worker-threads

[Tom de Vries <tdevries@suse.de>]

The default worker-threads is set to the number of hardware threads:
...
$ gdb -q -batch -ex "maint show worker-thread"
The number of worker threads GDB can use is the default (currently 8).
...
but does not take into account how many of those are actually available.

If we reduce the amount of available threads to 1, we get the same answer:
...
$ taskset -c 0 gdb -q -batch -ex "maint show worker-thread"
The number of worker threads GDB can use is the default (currently 8).
...

Fix this on linux using sched_getaffinity:
...
$ taskset -c 0 gdb -q -batch -ex "maint show worker-thread"
The number of worker threads GDB can use is the default (currently 1).
$ gdb -q -batch -ex "maint show worker-thread"
The number of worker threads GDB can use is the default (currently 8).
...
---
 gdb/maint.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/gdb/maint.c b/gdb/maint.c
index 1daa6ce1d2e..fbddfe15591 100644
--- a/gdb/maint.c
+++ b/gdb/maint.c
@@ -47,6 +47,10 @@
 #include "cli/cli-style.h"
 #include "cli/cli-cmds.h"
 
+#ifdef __linux__
+#include <sched.h>
+#endif
+
 static void maintenance_do_deprecate (const char *, int);
 
 #ifndef _WIN32
@@ -882,6 +886,20 @@ update_thread_pool_size ()
 	 systems.  */
       const int max_thread_count = 8;
       n_threads = std::min (hardware_threads, max_thread_count);
+
+      if (n_threads > 1)
+	{
+	  /* Exclude unavailable hardware threads (for instance made
+	     unavailable using taskset).  */
+#ifdef __linux__
+	  cpu_set_t cpus;
+	  int res = sched_getaffinity (getpid (), sizeof (cpu_set_t), &cpus);
+	  if (res == 0)
+	    n_threads = std::min (n_threads, CPU_COUNT (&cpus));
+#else
+	  /* Todo: handle other platforms.  */
+#endif
+	}
     }
 
   gdb::thread_pool::g_thread_pool->set_thread_count (n_threads);
-- 
2.51.0