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full change in implementing windows malloc support #3170

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3f8b592
full change in implementing windows malloc support
mar-yan24 Mar 12, 2026
35113d3
simultaneous thread winerr test fix
mar-yan24 Mar 12, 2026
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59 changes: 58 additions & 1 deletion src/engine/engine_util_errmem.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,13 +24,64 @@
#include <unistd.h>
#endif

#ifdef _WIN32
#include <windows.h>
#endif

#include "engine/engine_array_safety.h"
#include "engine/engine_macro.h"

//------------------------- cross-platform aligned malloc/free -------------------------------------

#ifdef _WIN32

// virtualalloc has 64KB min alloc granularity
#define MJU_LARGE_ALLOC_THRESHOLD (1 << 16)

static LONG CALLBACK mju_commitHandler(EXCEPTION_POINTERS* ep) {
if (ep->ExceptionRecord->ExceptionCode == EXCEPTION_ACCESS_VIOLATION) {
ULONG_PTR access_type = ep->ExceptionRecord->ExceptionInformation[0];
void* fault_addr = (void*)ep->ExceptionRecord->ExceptionInformation[1];
MEMORY_BASIC_INFORMATION mbi;
if (VirtualQuery(fault_addr, &mbi, sizeof(mbi)) != 0) {
// commit just the faulting page
if (mbi.State == MEM_RESERVE) {
if (VirtualAlloc(fault_addr, 1, MEM_COMMIT, PAGE_READWRITE)) {
return EXCEPTION_CONTINUE_EXECUTION;
}
}

if (mbi.State == MEM_COMMIT && (mbi.Protect & PAGE_READWRITE) && access_type != 8) {
return EXCEPTION_CONTINUE_EXECUTION;
}
}
}
return EXCEPTION_CONTINUE_SEARCH;
}

// register handler once, thread-safe bc of InitOnce
static INIT_ONCE mju_veh_init_once = INIT_ONCE_STATIC_INIT;

static BOOL CALLBACK mju_initVEH(INIT_ONCE* initOnce, void* param, void** ctx) {
AddVectoredExceptionHandler(1, mju_commitHandler);
return TRUE;
}

static void mju_ensureVEH(void) {
InitOnceExecuteOnce(&mju_veh_init_once, mju_initVEH, NULL, NULL);
}

#endif // _WIN32


static inline void* mju_alignedMalloc(size_t size, size_t align) {
#ifdef _WIN32
if (size >= MJU_LARGE_ALLOC_THRESHOLD) {
// install lazy-commit handler
mju_ensureVEH();
// MEM_RESERVE only: reserves virtual address space without commit charge
return VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_READWRITE);
}
return _aligned_malloc(size, align);
#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
return aligned_alloc(align, size);
Expand All @@ -39,7 +90,13 @@ static inline void* mju_alignedMalloc(size_t size, size_t align) {

static inline void mju_alignedFree(void* ptr) {
#ifdef _WIN32
_aligned_free(ptr);
// determine which allocator owns this pointer
MEMORY_BASIC_INFORMATION mbi;
if (VirtualQuery(ptr, &mbi, sizeof(mbi)) != 0 && mbi.AllocationBase == ptr) {
VirtualFree(ptr, 0, MEM_RELEASE);
} else {
_aligned_free(ptr);
}
#else
free(ptr);
#endif
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