118 lines
3.9 KiB
C++
118 lines
3.9 KiB
C++
#ifndef GREENLET_SLP_SWITCH_HPP
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#define GREENLET_SLP_SWITCH_HPP
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#include "greenlet_compiler_compat.hpp"
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#include "greenlet_refs.hpp"
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/*
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* the following macros are spliced into the OS/compiler
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* specific code, in order to simplify maintenance.
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*/
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// We can save about 10% of the time it takes to switch greenlets if
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// we thread the thread state through the slp_save_state() and the
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// following slp_restore_state() calls from
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// slp_switch()->g_switchstack() (which already needs to access it).
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//
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// However:
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//
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// that requires changing the prototypes and implementations of the
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// switching functions. If we just change the prototype of
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// slp_switch() to accept the argument and update the macros, without
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// changing the implementation of slp_switch(), we get crashes on
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// 64-bit Linux and 32-bit x86 (for reasons that aren't 100% clear);
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// on the other hand, 64-bit macOS seems to be fine. Also, 64-bit
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// windows is an issue because slp_switch is written fully in assembly
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// and currently ignores its argument so some code would have to be
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// adjusted there to pass the argument on to the
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// ``slp_save_state_asm()`` function (but interestingly, because of
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// the calling convention, the extra argument is just ignored and
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// things function fine, albeit slower, if we just modify
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// ``slp_save_state_asm`()` to fetch the pointer to pass to the
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// macro.)
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//
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// Our compromise is to use a *glabal*, untracked, weak, pointer
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// to the necessary thread state during the process of switching only.
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// This is safe because we're protected by the GIL, and if we're
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// running this code, the thread isn't exiting. This also nets us a
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// 10-12% speed improvement.
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static greenlet::Greenlet* volatile switching_thread_state = nullptr;
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#ifdef GREENLET_NOINLINE_SUPPORTED
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extern "C" {
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static int GREENLET_NOINLINE(slp_save_state_trampoline)(char* stackref);
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static void GREENLET_NOINLINE(slp_restore_state_trampoline)();
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}
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#define GREENLET_NOINLINE_INIT() \
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do { \
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} while (0)
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#else
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/* force compiler to call functions via pointers */
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/* XXX: Do we even want/need to support such compilers? This code path
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is untested on CI. */
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extern "C" {
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static int (slp_save_state_trampoline)(char* stackref);
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static void (slp_restore_state_trampoline)();
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}
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#define GREENLET_NOINLINE(name) cannot_inline_##name
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#define GREENLET_NOINLINE_INIT() \
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do { \
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slp_save_state_trampoline = GREENLET_NOINLINE(slp_save_state_trampoline); \
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slp_restore_state_trampoline = GREENLET_NOINLINE(slp_restore_state_trampoline); \
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} while (0)
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#endif
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#define SLP_SAVE_STATE(stackref, stsizediff) \
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do { \
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assert(switching_thread_state); \
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stackref += STACK_MAGIC; \
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if (slp_save_state_trampoline((char*)stackref)) \
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return -1; \
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if (!switching_thread_state->active()) \
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return 1; \
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stsizediff = switching_thread_state->stack_start() - (char*)stackref; \
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} while (0)
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#define SLP_RESTORE_STATE() slp_restore_state_trampoline()
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#define SLP_EVAL
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extern "C" {
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#define slp_switch GREENLET_NOINLINE(slp_switch)
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#include "slp_platformselect.h"
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}
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#undef slp_switch
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#ifndef STACK_MAGIC
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# error \
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"greenlet needs to be ported to this platform, or taught how to detect your compiler properly."
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#endif /* !STACK_MAGIC */
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#ifdef EXTERNAL_ASM
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/* CCP addition: Make these functions, to be called from assembler.
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* The token include file for the given platform should enable the
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* EXTERNAL_ASM define so that this is included.
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*/
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extern "C" {
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intptr_t
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slp_save_state_asm(intptr_t* ref)
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{
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intptr_t diff;
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SLP_SAVE_STATE(ref, diff);
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return diff;
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}
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void
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slp_restore_state_asm(void)
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{
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SLP_RESTORE_STATE();
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}
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extern int slp_switch(void);
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};
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#endif
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#endif
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