67 lines
2.1 KiB
C++
67 lines
2.1 KiB
C++
namespace factor
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{
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/* The callback heap is used to store the machine code that alien-callbacks
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actually jump to when C code invokes them.
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The callback heap has entries that look like code_blocks from the code heap, but
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callback heap entries are allocated contiguously, never deallocated, and all
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fields but the owner are set to false_object. The owner points to the callback
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bottom word, whose entry point is the callback body itself, generated by the
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optimizing compiler. The machine code that follows a callback stub consists of a
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single CALLBACK_STUB machine code template, which performs a jump to a "far"
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address (on PowerPC and x86-64, its loaded into a register first).
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GC updates the CALLBACK_STUB code if the code block of the callback bottom word
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is ever moved. The callback stub itself won't move, though, and is never
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deallocated. This means that the callback stub itself is a stable function
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pointer that C code can hold on to until the associated Factor VM exits.
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Since callback stubs are GC roots, and are never deallocated, the associated
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callback code in the code heap is also never deallocated.
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The callback heap is not saved in the image. Running GC in a new session after
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saving the image will deallocate any code heap entries that were only reachable
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from the callback heap in the previous session when the image was saved. */
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struct callback_heap {
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segment *seg;
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cell here;
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factor_vm *parent;
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explicit callback_heap(cell size, factor_vm *parent);
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~callback_heap();
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void *callback_entry_point(code_block *stub)
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{
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word *w = (word *)UNTAG(stub->owner);
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return w->entry_point;
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}
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void store_callback_operand(code_block *stub, cell index, cell value);
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void update(code_block *stub);
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code_block *add(cell owner, cell return_rewind);
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void update();
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code_block *next(code_block *stub)
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{
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return (code_block *)((cell)stub + stub->size());
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}
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template<typename Iterator> void each_callback(Iterator &iter)
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{
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code_block *scan = (code_block *)seg->start;
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code_block *end = (code_block *)here;
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while(scan < end)
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{
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iter(scan);
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scan = next(scan);
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}
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}
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};
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}
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