Fix race conditions with signal handlers and errno.
Be more systematic about preserving errno whenever a signal handler returns, even if it's not in the main thread. Do this by renaming signal handlers to distinguish between signal delivery and signal handling. All uses changed. * atimer.c (deliver_alarm_signal): Rename from alarm_signal_handler. * data.c (deliver_arith_signal): Rename from arith_error. * dispnew.c (deliver_window_change_signal): Rename from window_change_signal. * emacs.c (deliver_error_signal): Rename from fatal_error_signal. (deliver_danger_signal) [SIGDANGER]: Rename from memory_warning_signal. * keyboard.c (deliver_input_available_signal): Rename from input_available_signal. (deliver_user_signal): Rename from handle_user_signal. (deliver_interrupt_signal): Rename from interrupt_signal. * process.c (deliver_pipe_signal): Rename from send_process_trap. (deliver_child_signal): Rename from sigchld_handler. * atimer.c (handle_alarm_signal): * data.c (handle_arith_signal): * dispnew.c (handle_window_change_signal): * emacs.c (handle_fatal_signal, handle_danger_signal): * keyboard.c (handle_input_available_signal): * keyboard.c (handle_user_signal, handle_interrupt_signal): * process.c (handle_pipe_signal, handle_child_signal): New functions, with the actual signal-handling code taken from the original respective signal handlers, sans the sporadic attempts to preserve errno, since that's now done by handle_on_main_thread. * atimer.c (alarm_signal_handler): Remove unnecessary decl. * emacs.c, floatfns.c, lisp.h: Remove unused FLOAT_CATCH_SIGKILL cruft. * emacs.c (main_thread) [FORWARD_SIGNAL_TO_MAIN_THREAD]: Move to sysdep.c. (main) [FORWARD_SIGNAL_TO_MAIN_THREAD]: Move initialization of main_thread to sysdep.c's init_signals. * process.c (waitpid) [!WNOHANG]: #define to wait; that's good enough for our usage, and simplifies the mainline code. (record_child_status_change): New static function, as a helper for handle_child_signal, and with most of the old child handler's contents. (CAN_HANDLE_MULTIPLE_CHILDREN): New constant. (handle_child_signal): Use the above. * sysdep.c (main_thread) [FORWARD_SIGNAL_TO_MAIN_THREAD]: Moved here from emacs.c. (init_signals) [FORWARD_SIGNAL_TO_MAIN_THREAD]: Initialize it; code moved here from emacs.c's main function. * sysdep.c, syssignal.h (handle_on_main_thread): New function, replacing the old SIGNAL_THREAD_CHECK. All uses changed. This lets callers save and restore errno properly.
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