add emscripten WASM support; this PR #822 written by Alon Zakai @kripken

src/prim/emscripten/prim.c

@@ -0,0 +1,251 @@
+/* ----------------------------------------------------------------------------
+Copyright (c) 2018-2023, Microsoft Research, Daan Leijen, Alon Zakai
+This is free software; you can redistribute it and/or modify it under the
+terms of the MIT license. A copy of the license can be found in the file
+"LICENSE" at the root of this distribution.
+-----------------------------------------------------------------------------*/
+
+// This file is included in `src/prim/prim.c`
+
+#include "mimalloc.h"
+#include "mimalloc/internal.h"
+#include "mimalloc/atomic.h"
+#include "mimalloc/prim.h"
+
+// Design
+// ======
+//
+// mimalloc is built on top of emmalloc. emmalloc is a minimal allocator on top
+// of sbrk. The reason for having three layers here is that we want mimalloc to
+// be able to allocate and release system memory properly, the same way it would
+// when using VirtualAlloc on Windows or mmap on POSIX, and sbrk is too limited.
+// Specifically, sbrk can only go up and down, and not "skip" over regions, and
+// so we end up either never freeing memory to the system, or we can get stuck
+// with holes.
+//
+// Atm wasm generally does *not* free memory back the system: once grown, we do
+// not shrink back down (https://github.com/WebAssembly/design/issues/1397).
+// However, that is expected to improve
+// (https://github.com/WebAssembly/memory-control/blob/main/proposals/memory-control/Overview.md)
+// and so we do not want to bake those limitations in here.
+//
+// Even without that issue, we want our system allocator to handle holes, that
+// is, it should merge freed regions and allow allocating new content there of
+// the full size, etc., so that we do not waste space. That means that the
+// system allocator really does need to handle the general problem of allocating
+// and freeing variable-sized chunks of memory in a random order, like malloc/
+// free do. And so it makes sense to layer mimalloc on top of such an
+// implementation.
+//
+// emmalloc makes sense for the lower level because it is small and simple while
+// still fully handling merging of holes etc. It is not the most efficient
+// allocator, but our assumption is that mimalloc needs to be fast while the
+// system allocator underneath it is called much less frequently.
+//
+
+//---------------------------------------------
+// init
+//---------------------------------------------
+
+void _mi_prim_mem_init( mi_os_mem_config_t* config) {
+  config->page_size = 64*MI_KiB; // WebAssembly has a fixed page size: 64KiB
+  config->alloc_granularity = 16;
+  config->has_overcommit = false;
+  config->must_free_whole = true;
+  config->has_virtual_reserve = false;
+}
+
+extern void emmalloc_free(void*);
+
+int _mi_prim_free(void* addr, size_t size) {
+  MI_UNUSED(size);
+  emmalloc_free(addr);
+  return 0;
+}
+
+
+//---------------------------------------------
+// Allocation
+//---------------------------------------------
+
+extern void* emmalloc_memalign(size_t, size_t);
+
+// Note: the `try_alignment` is just a hint and the returned pointer is not guaranteed to be aligned.
+int _mi_prim_alloc(size_t size, size_t try_alignment, bool commit, bool allow_large, bool* is_large, bool* is_zero, void** addr) {
+  MI_UNUSED(try_alignment); MI_UNUSED(allow_large); MI_UNUSED(commit);
+  *is_large = false;
+  // TODO: Track the highest address ever seen; first uses of it are zeroes.
+  //       That assumes no one else uses sbrk but us (they could go up,
+  //       scribble, and then down), but we could assert on that perhaps.
+  *is_zero = false;
+  // emmalloc has some limitations on alignment size.
+  // TODO: Why does mimalloc ask for an align of 4MB? that ends up allocating
+  //       8, which wastes quite a lot for us in wasm. If that is unavoidable,
+  //       we may want to improve emmalloc to support such alignment. See also
+  //       https://github.com/emscripten-core/emscripten/issues/20645
+  #define MIN_EMMALLOC_ALIGN           8
+  #define MAX_EMMALLOC_ALIGN (1024*1024)
+  if (try_alignment < MIN_EMMALLOC_ALIGN) {
+    try_alignment = MIN_EMMALLOC_ALIGN;
+  } else if (try_alignment > MAX_EMMALLOC_ALIGN) {
+    try_alignment = MAX_EMMALLOC_ALIGN;
+  }
+  void* p = emmalloc_memalign(try_alignment, size);
+  *addr = p;
+  if (p == 0) {
+    return ENOMEM;
+  }
+  return 0;
+}
+
+
+//---------------------------------------------
+// Commit/Reset
+//---------------------------------------------
+
+int _mi_prim_commit(void* addr, size_t size, bool* is_zero) {
+  MI_UNUSED(addr); MI_UNUSED(size);
+  // See TODO above.
+  *is_zero = false;
+  return 0;
+}
+
+int _mi_prim_decommit(void* addr, size_t size, bool* needs_recommit) {
+  MI_UNUSED(addr); MI_UNUSED(size);
+  *needs_recommit = false;
+  return 0;
+}
+
+int _mi_prim_reset(void* addr, size_t size) {
+  MI_UNUSED(addr); MI_UNUSED(size);
+  return 0;
+}
+
+int _mi_prim_protect(void* addr, size_t size, bool protect) {
+  MI_UNUSED(addr); MI_UNUSED(size); MI_UNUSED(protect);
+  return 0;
+}
+
+
+//---------------------------------------------
+// Huge pages and NUMA nodes
+//---------------------------------------------
+
+int _mi_prim_alloc_huge_os_pages(void* hint_addr, size_t size, int numa_node, bool* is_zero, void** addr) {
+  MI_UNUSED(hint_addr); MI_UNUSED(size); MI_UNUSED(numa_node);
+  *is_zero = true;
+  *addr = NULL;
+  return ENOSYS;
+}
+
+size_t _mi_prim_numa_node(void) {
+  return 0;
+}
+
+size_t _mi_prim_numa_node_count(void) {
+  return 1;
+}
+
+
+//----------------------------------------------------------------
+// Clock
+//----------------------------------------------------------------
+
+#include <emscripten/html5.h>
+
+mi_msecs_t _mi_prim_clock_now(void) {
+  return emscripten_date_now();
+}
+
+
+//----------------------------------------------------------------
+// Process info
+//----------------------------------------------------------------
+
+void _mi_prim_process_info(mi_process_info_t* pinfo)
+{
+  // use defaults
+  MI_UNUSED(pinfo);
+}
+
+
+//----------------------------------------------------------------
+// Output
+//----------------------------------------------------------------
+
+#include <emscripten/console.h>
+
+void _mi_prim_out_stderr( const char* msg) {
+  emscripten_console_error(msg);
+}
+
+
+//----------------------------------------------------------------
+// Environment
+//----------------------------------------------------------------
+
+bool _mi_prim_getenv(const char* name, char* result, size_t result_size) {
+  // For code size reasons, do not support environ customization for now.
+  MI_UNUSED(name);
+  MI_UNUSED(result);
+  MI_UNUSED(result_size);
+  return false;
+}
+
+
+//----------------------------------------------------------------
+// Random
+//----------------------------------------------------------------
+
+bool _mi_prim_random_buf(void* buf, size_t buf_len) {
+  int err = getentropy(buf, buf_len);
+  return !err;
+}
+
+
+//----------------------------------------------------------------
+// Thread init/done
+//----------------------------------------------------------------
+
+#ifdef __EMSCRIPTEN_SHARED_MEMORY__
+
+// use pthread local storage keys to detect thread ending
+// (and used with MI_TLS_PTHREADS for the default heap)
+pthread_key_t _mi_heap_default_key = (pthread_key_t)(-1);
+
+static void mi_pthread_done(void* value) {
+  if (value!=NULL) {
+    _mi_thread_done((mi_heap_t*)value);
+  }
+}
+
+void _mi_prim_thread_init_auto_done(void) {
+  mi_assert_internal(_mi_heap_default_key == (pthread_key_t)(-1));
+  pthread_key_create(&_mi_heap_default_key, &mi_pthread_done);
+}
+
+void _mi_prim_thread_done_auto_done(void) {
+  // nothing to do
+}
+
+void _mi_prim_thread_associate_default_heap(mi_heap_t* heap) {
+  if (_mi_heap_default_key != (pthread_key_t)(-1)) {  // can happen during recursive invocation on freeBSD
+    pthread_setspecific(_mi_heap_default_key, heap);
+  }
+}
+
+#else
+
+void _mi_prim_thread_init_auto_done(void) {
+  // nothing
+}
+
+void _mi_prim_thread_done_auto_done(void) {
+  // nothing
+}
+
+void _mi_prim_thread_associate_default_heap(mi_heap_t* heap) {
+  MI_UNUSED(heap);
+
+}
+#endif

src/prim/prim.c

@@ -18,6 +18,9 @@ terms of the MIT license. A copy of the license can be found in the file
 #define MI_USE_SBRK
 #include "wasi/prim.c"     // memory-grow or sbrk (Wasm)
 
+#elif defined(__EMSCRIPTEN__)
+#include "emscripten/prim.c" // emmalloc_*, + pthread support
+
 #else
 #include "unix/prim.c"     // mmap() (Linux, macOSX, BSD, Illumnos, Haiku, DragonFly, etc.)