a PariThreadPool to handle multithreading via Python

Author: videlec

.gitignore

@@ -13,6 +13,7 @@ cypari2/handle_error.c
 cypari2/pari_instance.c
 cypari2/stack.c
 cypari2/string_utils.c
+cypari2/threads.c
 
 # Byte-compiled / optimized / DLL files
 __pycache__/

cypari2/__init__.py

@@ -1,3 +1,4 @@
 from .pari_instance import Pari
 from .handle_error import PariError
 from .gen import Gen
+from .threads import PariThreadPool

cypari2/stack.pyx

@@ -209,7 +209,10 @@ cdef Gen new_gen_noclear(GEN x):
         elif isclone(x):
             gclone_refc(x)
             return Gen_new(x, x)
-        raise SystemError("new_gen() argument not on PARI stack, not on PARI heap and not a universal constant")
+        else:
+            # NOTE: it might be the case that x belongs to a local stack of a thread
+            # In that case we copy it in the main stack
+            x = gcopy(x)
 
     z = Gen_stack_new(x)
 

cypari2/threads.pxd

@@ -0,0 +1,6 @@
+from .types cimport *
+
+cdef class PariThreadPool:
+    cdef size_t nbthreads
+    cdef pari_thread * pths
+    cdef size_t ithread

cypari2/threads.pyx

@@ -0,0 +1,72 @@
+r"""
+Multithreading from Python
+"""
+
+from libc.stdlib cimport malloc, calloc, free
+
+from .types cimport *
+from .paridecl cimport *
+from gen cimport Gen, objtogen
+
+cdef class PariThreadPool:
+    r"""
+    Pari thread allocator
+
+    This class is intended to be used in conjunction with the multithreading
+    capabilities of the ``ThreadPoolExecutor`` from the ``concurrent.futures``
+    Python library.
+
+    Examples:
+
+    >>> from concurrent.futures import ThreadPoolExecutor, as_completed
+    >>> from cypari2 import Pari, PariThreadPool
+    >>> pari = Pari()
+    >>> pari.default('nbthreads', 1)
+    >>> max_workers = 4
+    >>> pari_pool = PariThreadPool(max_workers)
+    >>> square_free = []
+    >>> with ThreadPoolExecutor(max_workers=max_workers, initializer=pari_pool.initializer) as executor:
+    ...     futures = {executor.submit(pari.issquarefree, n): n for n in range(10**6, 10**6 + 1000)}
+    ...     for future in as_completed(futures):
+    ...         n = futures[future]
+    ...         if future.result():
+    ...             square_free.append(n)
+    >>> square_free.sort()
+    >>> square_free
+    [1000001, 1000002, 1000003, 1000005, 1000006, ..., 1000994, 1000995, 1000997, 1000999]
+    """
+    def __init__(self, size_t nbthreads, size_t size=8000000, size_t sizemax=0):
+        r"""
+        INPUT:
+
+        - ``nbthreads`` -- the number of threads to allocate
+
+        - ``size`` -- (default: 8000000) the number of bytes for the
+          initial PARI stack (see notes below)
+
+        - ``sizemax`` -- (default: 0) the maximal number of bytes for the
+          dynamically increasing PARI stack.
+        """
+        cdef size_t i
+        size = max(size, pari_mainstack.rsize)
+        sizemax = max(max(size, pari_mainstack.vsize), sizemax)
+        self.pths = <pari_thread *> calloc(nbthreads, sizeof(pari_thread))
+        for i in range(nbthreads):
+            pari_thread_valloc(self.pths + i, size, sizemax, NULL)
+        self.ithread = 0
+        self.nbthreads = nbthreads
+
+    def __dealloc__(self):
+        cdef size_t i
+        for i in range(self.ithread):
+            pari_thread_free(self.pths + i)
+        free(self.pths)
+
+    def __repr__(self):
+        return 'Pari thread pool with {} threads'.format(self.nbthreads)
+
+    def initializer(self):
+        if self.ithread >= self.nbthreads:
+            raise ValueError('no more thread available')
+        pari_thread_start(self.pths + self.ithread)
+        self.ithread += 1

cypari2/types.pxd

@@ -125,7 +125,8 @@ cdef extern from "pari/pari.h":
     struct pariFILE
     struct pari_mt
     struct pari_stack
-    struct pari_thread
+    struct pari_thread:
+        pass
     struct pari_timer
     struct GENbin
     struct hashentry

docs/source/threads.rst

@@ -0,0 +1,2 @@
+.. automodule:: cypari2.threads
+    :members:

tests/rundoctest.py

@@ -29,7 +29,7 @@
 attempted = 0
 for mod in [cypari2.closure, cypari2.convert, cypari2.gen,
             cypari2.handle_error, cypari2.pari_instance, cypari2.stack,
-            cypari2.string_utils,
+            cypari2.string_utils, cypari2.threads,
             autogen.doc, autogen.generator, autogen.parser,
             autogen.paths]: