revert to old (non-resizable) thread pool

python/misc.cc

@@ -203,8 +203,6 @@ py::array py_transpose(const py::array &in, py::array &out)
   MR_fail("unsupported datatype");
   }
 
-void py_set_thread_pool_size(size_t new_pool_size)
-  { set_pool_size(new_pool_size); }
 
 const char *misc_DS = R"""(
 Various unsorted utilities
@@ -227,8 +225,6 @@ void add_misc(py::module &msup)
 
   m.def("ascontiguousarray",&py_ascontiguousarray, "in"_a);
   m.def("transpose",&py_transpose, "in"_a, "out"_a);
-
-  m.def("set_thread_pool_size",&py_set_thread_pool_size, "new_pool_size"_a);
   }
 
 }

src/ducc0/infra/threading.cc

@@ -29,7 +29,6 @@
 #include <queue>
 #include <atomic>
 #include <vector>
-#include <memory>
 #if __has_include(<pthread.h>)
 #include <pthread.h>
 #endif
@@ -41,7 +40,9 @@ namespace detail_threading {
 
 #ifndef DUCC0_NO_THREADING
 
-std::atomic<size_t> default_nthreads_(std::max<size_t>(1, std::thread::hardware_concurrency()));
+static const size_t max_threads_ = std::max<size_t>(1, std::thread::hardware_concurrency());
+
+std::atomic<size_t> default_nthreads_(max_threads_);
 
 size_t get_default_nthreads()
   { return default_nthreads_; }
@@ -49,6 +50,8 @@ size_t get_default_nthreads()
 void set_default_nthreads(size_t new_default_nthreads)
   { default_nthreads_ = std::max<size_t>(1, new_default_nthreads); }
 
+size_t max_threads() { return max_threads_; }
+
 class latch
   {
     std::atomic<size_t> num_left_;
@@ -152,9 +155,9 @@ class thread_pool
       threads_(nthreads)
       { create_threads(); }
 
-    ~thread_pool() { shutdown(); }
+    thread_pool(): thread_pool(max_threads_) {}
 
-    size_t size() const { return threads_.size(); }
+    ~thread_pool() { shutdown(); }
 
     void submit(std::function<void()> work)
       {
@@ -176,12 +179,9 @@ class thread_pool
       }
   };
 
-thread_pool &get_pool(size_t nthreads=0)
+inline thread_pool &get_pool()
   {
-  static std::unique_ptr<thread_pool> pool;
-  if ((!pool) && (nthreads==0)) nthreads=default_nthreads_;
-  if ((!pool) || ((nthreads!=0) && (nthreads!=pool->size()))) // resize
-    pool = std::make_unique<thread_pool>(nthreads);
+  static thread_pool pool;
 #if __has_include(<pthread.h>)
   static std::once_flag f;
   call_once(f,
@@ -194,12 +194,9 @@ thread_pool &get_pool(size_t nthreads=0)
     });
 #endif
 
-  return *pool;
+  return pool;
   }
 
-void set_pool_size(size_t new_pool_size)
-  { get_pool(new_pool_size); }
-
 class Distribution
   {
   private:
@@ -320,7 +317,7 @@ void Distribution::thread_map(std::function<void(Scheduler &)> f)
     return;
     }
 
-  auto &pool = get_pool();
+  auto & pool = get_pool();
   latch counter(nthreads_);
   std::exception_ptr ex;
   std::mutex ex_mut;

src/ducc0/infra/threading.h

@@ -47,11 +47,10 @@ class Scheduler
     virtual Range getNext() = 0;
   };
 
+size_t max_threads();
 void set_default_nthreads(size_t new_default_nthreads);
 size_t get_default_nthreads();
 
-void set_pool_size(size_t new_pool_size);
-
 void execSingle(size_t nwork,
   std::function<void(Scheduler &)> func);
 void execStatic(size_t nwork, size_t nthreads, size_t chunksize,
@@ -64,7 +63,7 @@ void execParallel(size_t nthreads, std::function<void(Scheduler &)> func);
 
 } // end of namespace detail_threading
 
-using detail_threading::set_pool_size;
+using detail_threading::max_threads;
 using detail_threading::get_default_nthreads;
 using detail_threading::set_default_nthreads;
 using detail_threading::Scheduler;