bRPC源码解析·bthread机制

/* bthread/bthread/stack.h */
struct ContextualStack {
    bthread_fcontext_t context;
    StackType stacktype;
    StackStorage storage;
};

enum StackType {
    STACK_TYPE_MAIN = 0,
    STACK_TYPE_PTHREAD = BTHREAD_STACKTYPE_PTHREAD,
    STACK_TYPE_SMALL = BTHREAD_STACKTYPE_SMALL,
    STACK_TYPE_NORMAL = BTHREAD_STACKTYPE_NORMAL,
    STACK_TYPE_LARGE = BTHREAD_STACKTYPE_LARGE
};

struct StackStorage {
    int stacksize;
    int guardsize;
    // Assume stack grows upwards.
    // http://www.boost.org/doc/libs/1_55_0/libs/context/doc/html/context/stack.html
    void* bottom;
    unsigned valgrind_stack_id;

    // Clears all members.
    void zeroize() {
        stacksize = 0;
        guardsize = 0;
        bottom = NULL;
        valgrind_stack_id = 0;
    }
};

/* bthread/bthread/stack_inl.h */
template <typename StackClass> struct StackFactory {
    struct Wrapper : public ContextualStack {
        explicit Wrapper(void (*entry)(intptr_t)) {
            if (allocate_stack_storage(&storage, *StackClass::stack_size_flag,
                                       FLAGS_guard_page_size) != 0) {
                storage.zeroize();
                context = NULL;
                return;
            }

            context = bthread_make_fcontext(storage.bottom, storage.stacksize, entry);
            stacktype = (StackType)StackClass::stacktype;
        }
        ...
    };
    ...
};

#if defined(BTHREAD_CONTEXT_PLATFORM_linux_x86_64) && defined(BTHREAD_CONTEXT_COMPILER_gcc)
__asm (
".text\n"
".globl bthread_make_fcontext\n"
".type bthread_make_fcontext,@function\n"
".align 16\n"
"bthread_make_fcontext:\n"
"    movq  %rdi, %rax\n"
"    andq  $-16, %rax\n"
"    leaq  -0x48(%rax), %rax\n"
"    movq  %rdx, 0x38(%rax)\n"
"    stmxcsr  (%rax)\n"
"    fnstcw   0x4(%rax)\n"
"    leaq  finish(%rip), %rcx\n"
"    movq  %rcx, 0x40(%rax)\n"
"    ret \n"
"finish:\n"
"    xorq  %rdi, %rdi\n"
"    call  _exit@PLT\n"
"    hlt\n"
".size bthread_make_fcontext,.-bthread_make_fcontext\n"
".section .note.GNU-stack,\"\",%progbits\n"
);

#endif

inline void jump_stack(ContextualStack* from, ContextualStack* to) {
    bthread_jump_fcontext(&from->context, to->context, 0/*not skip remained*/);
}

intptr_t BTHREAD_CONTEXT_CALL_CONVENTION
bthread_jump_fcontext(bthread_fcontext_t * ofc, bthread_fcontext_t nfc,
                      intptr_t vp, bool preserve_fpu = false);
#if defined(BTHREAD_CONTEXT_PLATFORM_linux_x86_64) && defined(BTHREAD_CONTEXT_COMPILER_gcc)
__asm (
".text\n"
".globl bthread_jump_fcontext\n"
".type bthread_jump_fcontext,@function\n"
".align 16\n"
"bthread_jump_fcontext:\n"
"    pushq  %rbp  \n"
"    pushq  %rbx  \n"
"    pushq  %r15  \n"
"    pushq  %r14  \n"
"    pushq  %r13  \n"
"    pushq  %r12  \n"
"    leaq  -0x8(%rsp), %rsp\n"
"    cmp  $0, %rcx\n"
"    je  1f\n"
"    stmxcsr  (%rsp)\n"
"    fnstcw   0x4(%rsp)\n"
"1:\n"
"    movq  %rsp, (%rdi)\n"
"    movq  %rsi, %rsp\n"
"    cmp  $0, %rcx\n"
"    je  2f\n"
"    ldmxcsr  (%rsp)\n"
"    fldcw  0x4(%rsp)\n"
"2:\n"
"    leaq  0x8(%rsp), %rsp\n"
"    popq  %r12  \n"
"    popq  %r13  \n"
"    popq  %r14  \n"
"    popq  %r15  \n"
"    popq  %rbx  \n"
"    popq  %rbp  \n"
"    popq  %r8\n"
"    movq  %rdx, %rax\n"
"    movq  %rdx, %rdi\n"
"    jmp  *%r8\n"
".size bthread_jump_fcontext,.-bthread_jump_fcontext\n"
".section .note.GNU-stack,\"\",%progbits\n"
);

#endif