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<title>Vulkan Memory Allocator: General considerations</title>
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<div class="title">General considerations </div> </div>
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<div class="textblock"><h1><a class="anchor" id="general_considerations_thread_safety"></a>
Thread safety</h1>
<li>The library has no global state, so separate <a class="el" href="struct_vma_allocator.html" title="Represents main object of this library initialized. ">VmaAllocator</a> objects can be used independently. There should be no need to create multiple such objects though - one per <code>VkDevice</code> is enough.</li>
<li>By default, all calls to functions that take <a class="el" href="struct_vma_allocator.html" title="Represents main object of this library initialized. ">VmaAllocator</a> as first parameter are safe to call from multiple threads simultaneously because they are synchronized internally when needed.</li>
<li>When the allocator is created with <a class="el" href="vk__mem__alloc_8h.html#a4f87c9100d154a65a4ad495f7763cf7ca4816ddaed324ba110172ca608a20f29d" title="Allocator and all objects created from it will not be synchronized internally, so you must guarantee ...">VMA_ALLOCATOR_CREATE_EXTERNALLY_SYNCHRONIZED_BIT</a> flag, calls to functions that take such <a class="el" href="struct_vma_allocator.html" title="Represents main object of this library initialized. ">VmaAllocator</a> object must be synchronized externally.</li>
<li>Access to a <a class="el" href="struct_vma_allocation.html" title="Represents single memory allocation. ">VmaAllocation</a> object must be externally synchronized. For example, you must not call <a class="el" href="vk__mem__alloc_8h.html#a86dd08aba8633bfa4ad0df2e76481d8b" title="Returns current information about specified allocation and atomically marks it as used in current fra...">vmaGetAllocationInfo()</a> and <a class="el" href="vk__mem__alloc_8h.html#ad5bd1243512d099706de88168992f069" title="Maps memory represented by given allocation and returns pointer to it. ">vmaMapMemory()</a> from different threads at the same time if you pass the same <a class="el" href="struct_vma_allocation.html" title="Represents single memory allocation. ">VmaAllocation</a> object to these functions.</li>
<h1><a class="anchor" id="general_considerations_allocation_algorithm"></a>
Allocation algorithm</h1>
<p>The library uses following algorithm for allocation, in order:</p>
<ol type="1">
<li>Try to find free range of memory in existing blocks.</li>
<li>If failed, try to create a new block of <code>VkDeviceMemory</code>, with preferred block size.</li>
<li>If failed, try to create such block with size/2, size/4, size/8.</li>
<li>If failed and <a class="el" href="vk__mem__alloc_8h.html#ad9889c10c798b040d59c92f257cae597a68686d0ce9beb0d4d1b9f2b8b1389a7e">VMA_ALLOCATION_CREATE_CAN_MAKE_OTHER_LOST_BIT</a> flag was specified, try to find space in existing blocks, possilby making some other allocations lost.</li>
<li>If failed, try to allocate separate <code>VkDeviceMemory</code> for this allocation, just like when you use <a class="el" href="vk__mem__alloc_8h.html#ad9889c10c798b040d59c92f257cae597a3fc311d855c2ff53f1090ef5c722b38f" title="Set this flag if the allocation should have its own memory block. ">VMA_ALLOCATION_CREATE_DEDICATED_MEMORY_BIT</a>.</li>
<li>If failed, choose other memory type that meets the requirements specified in <a class="el" href="struct_vma_allocation_create_info.html">VmaAllocationCreateInfo</a> and go to point 1.</li>
<li>If failed, return <code>VK_ERROR_OUT_OF_DEVICE_MEMORY</code>.</li>
<h1><a class="anchor" id="general_considerations_features_not_supported"></a>
Features not supported</h1>
<p>Features deliberately excluded from the scope of this library:</p>
<li>Data transfer - issuing commands that transfer data between buffers or images, any usage of <code>VkCommandList</code> or <code>VkCommandQueue</code> and related synchronization is responsibility of the user.</li>
<li>Support for any programming languages other than C/C++. Bindings to other languages are welcomed as external projects. </li>
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