MemoryTrim.cpp

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// Copyright (c) 2008-2025 OpenShot Studios, LLC
//
// SPDX-License-Identifier: LGPL-3.0-or-later
 
#include "MemoryTrim.h"
 
#include <atomic>
#include <chrono>
#include <cstdint>
 
#if defined(__GLIBC__)
#include <malloc.h>
#elif defined(_WIN32)
#include <malloc.h>
#elif defined(__APPLE__)
#include <malloc/malloc.h>
#endif
 
namespace {
// Limit trim attempts to once per interval to avoid spamming platform calls
constexpr uint64_t kMinTrimIntervalMs = 30000; // 30s debounce
std::atomic<uint64_t> g_last_trim_ms{0};
std::atomic<bool> g_trim_in_progress{false};
 
uint64_t NowMs() {
    using namespace std::chrono;
    return duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
}
}  // namespace
 
namespace openshot {
 
bool TrimMemoryToOS() noexcept {
    const uint64_t now_ms = NowMs();
    const uint64_t last_ms = g_last_trim_ms.load(std::memory_order_relaxed);
 
    // Skip if we recently trimmed
    if (now_ms - last_ms < kMinTrimIntervalMs)
        return false;
 
    // Only one trim attempt runs at a time
    bool expected = false;
    if (!g_trim_in_progress.compare_exchange_strong(expected, true, std::memory_order_acq_rel))
        return false;
 
    bool did_trim = false;
 
#if defined(__GLIBC__)
    // GLIBC exposes malloc_trim to release free arenas back to the OS
    malloc_trim(0);
    did_trim = true;
#elif defined(_WIN32)
    // MinGW/MSYS2 expose _heapmin to compact the CRT heap
    _heapmin();
    did_trim = true;
#elif defined(__APPLE__)
    // macOS uses the malloc zone API to relieve memory pressure
    malloc_zone_t* zone = malloc_default_zone();
    malloc_zone_pressure_relief(zone, 0);
    did_trim = true;
#else
    // Platforms without a known trimming API
    did_trim = false;
#endif
 
    if (did_trim) {
        g_last_trim_ms.store(now_ms, std::memory_order_relaxed);
    }
 
    g_trim_in_progress.store(false, std::memory_order_release);
    return did_trim;
}
 
}  // namespace openshot