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