Function SuspendThreads

pydevd_attach_to_process/windows/attach.cpp:203–262

Suspends all threads ensuring that they are not currently in a call to Py_AddPendingCall.

// Suspends all threads ensuring that they are not currently in a call to Py_AddPendingCall.
void SuspendThreads(ThreadMap &suspendedThreads, Py_AddPendingCall* addPendingCall, PyEval_ThreadsInitialized* threadsInited) {
    DWORD curThreadId = GetCurrentThreadId();
    DWORD curProcess = GetCurrentProcessId();
    // suspend all the threads in the process so we can do things safely...
    bool suspended;

    do {
        suspended = false;
        HANDLE h = CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, 0);
        if (h != INVALID_HANDLE_VALUE) {

            THREADENTRY32 te;
            te.dwSize = sizeof(te);
            if (Thread32First(h, &te)) {
                do {
                    if (te.dwSize >= FIELD_OFFSET(THREADENTRY32, th32OwnerProcessID) + sizeof(te.th32OwnerProcessID) && te.th32OwnerProcessID == curProcess) {


                        if (te.th32ThreadID != curThreadId && suspendedThreads.find(te.th32ThreadID) == suspendedThreads.end()) {
                            auto hThread = OpenThread(THREAD_ALL_ACCESS, FALSE, te.th32ThreadID);
                            if (hThread != nullptr) {
                                SuspendThread(hThread);

                                bool addingPendingCall = false;

                                CONTEXT context;
                                memset(&context, 0x00, sizeof(CONTEXT));
                                context.ContextFlags = CONTEXT_ALL;
                                GetThreadContext(hThread, &context);

#if defined(_X86_)
                                if (context.Eip >= *(reinterpret_cast<DWORD*>(addPendingCall)) && context.Eip <= (*(reinterpret_cast<DWORD*>(addPendingCall))) + 0x100) {
                                    addingPendingCall = true;
                                }
#elif defined(_AMD64_)
                                if (context.Rip >= *(reinterpret_cast<DWORD64*>(addPendingCall)) && context.Rip <= *(reinterpret_cast<DWORD64*>(addPendingCall) + 0x100)) {
                                    addingPendingCall = true;
                                }
#endif

                                if (addingPendingCall) {
                                    // we appear to be adding a pending call via this thread - wait for this to finish so we can add our own pending call...
                                    ResumeThread(hThread);
                                    SwitchToThread();   // yield to the resumed thread if it's on our CPU...
                                    CloseHandle(hThread);
                                } else {
                                    suspendedThreads[te.th32ThreadID] = hThread;
                                }
                                suspended = true;
                            }
                        }
                    }

                    te.dwSize = sizeof(te);
                } while (Thread32Next(h, &te) && !threadsInited());
            }
            CloseHandle(h);
        }