add realloc to MKLMemory

as atomics are a c11+ feature, specific flags are needed to enable on window

Author: ndgrigorian

meson.build

@@ -7,6 +7,7 @@ project(
         check: true
     ).stdout().strip(),
     default_options: [
+        'c_std=c11',
         'buildtype=release',
     ]
 )
@@ -18,6 +19,13 @@ c_args = ['-DNDEBUG']
 thread_dep = dependency('threads')
 
 cc = meson.get_compiler('c')
+if cc.get_id() == 'msvc'
+    add_project_arguments(
+        '/experimental:c11atomics',
+        language: 'c'
+    )
+endif
+
 mkl_dep = dependency('MKL', method: 'cmake',
     modules: ['MKL::MKL'],
     cmake_args: [

mkl/_mkl_memory.pyx

@@ -31,16 +31,25 @@ import numbers
 from cpython cimport Py_buffer
 from libc.string cimport memcpy
 
-from mkl._mkl_service cimport mkl_malloc, mkl_free
+from mkl._mkl_service cimport mkl_malloc, mkl_realloc, mkl_free
+
+cdef extern from "stdatomic.h" nogil:
+    ctypedef int atomic_int "_Atomic int"
+    void atomic_init(atomic_int *obj, int value)
+    int atomic_fetch_add(atomic_int *obj, int value)
+    int atomic_fetch_sub(atomic_int *obj, int value)
+    int atomic_load(atomic_int *obj)
 
 
 cdef class MKLMemory:
     cdef void *_memory_ptr
     cdef Py_ssize_t nbytes
+    cdef atomic_int exported_buffers
 
     cdef _cinit_empty(self):
         self._memory_ptr = NULL
         self.nbytes = 0
+        atomic_init(&self.exported_buffers, 0)
 
     cdef _cinit_alloc(self, Py_ssize_t nbytes, Py_ssize_t alignment):
         self._cinit_empty()
@@ -100,5 +109,23 @@ cdef class MKLMemory:
         buffer.strides = &buffer.itemsize
         buffer.suboffsets = NULL                # for pointer arrays only
 
+        atomic_fetch_add(&self.exported_buffers, 1)
+
     def __releasebuffer__(self, Py_buffer *buffer):
-        pass
+        atomic_fetch_sub(&self.exported_buffers, 1)
+
+    def realloc(self, Py_ssize_t new_nbytes):
+        if atomic_load(&self.exported_buffers) > 0:
+            raise BufferError("Cannot realloc memory while there are exported buffers.")
+        if new_nbytes <= 0:
+            raise ValueError("New number of bytes must be positive.")
+
+        cdef void *p
+        with nogil:
+            p = mkl_realloc(self._memory_ptr, new_nbytes)
+
+        if not p:
+            raise MemoryError("MKL memory reallocation failed.")
+
+        self._memory_ptr = p
+        self.nbytes = new_nbytes

mkl/_mkl_service.pxd

@@ -152,6 +152,7 @@ cdef extern from "mkl.h":
     MKL_INT64 mkl_peak_mem_usage(int mode)
     int mkl_set_memory_limit(int mem_type, size_t limit)
     void *mkl_malloc(size_t size, int alignment) nogil
+    void *mkl_realloc(void *ptr, size_t size) nogil
     void mkl_free(void *ptr) nogil
 
     # Conditional Numerical Reproducibility