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f7129481ed
* Handle not found "select()" symbol if dlsym() return NULL * Handle minimum wait time if remaining time < designated minimum sleep time
96 lines
2.9 KiB
C
96 lines
2.9 KiB
C
/*
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* SPDX-FileCopyrightText: 2023-2024 Espressif Systems (Shanghai) CO LTD
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <freertos/FreeRTOS.h>
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#include <freertos/task.h>
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#include <dlfcn.h>
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#include <assert.h>
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#include <sys/select.h>
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#include <errno.h>
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/** This module addresses the FreeRTOS simulator's coexistence with Linux system calls from user apps.
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* It wraps select so that it doesn't block the FreeRTOS task calling it, so that the
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* scheduler will allow lower priority tasks to run.
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* Without the wrapper, most components such as ESP-MQTT block lower priority tasks from running at all.
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*/
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typedef int (*select_func_t)(int fd, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeval *tval);
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int select(int fd, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeval *tval)
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{
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static select_func_t s_real_select = NULL;
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TickType_t end_ticks = portMAX_DELAY;
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fd_set o_rfds, o_wfds, o_efds;
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// Lookup the select symbol
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if (s_real_select == NULL) {
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s_real_select = (select_func_t)dlsym(RTLD_NEXT, "select");
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assert(s_real_select); // abort() if we cannot locate the symbol
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}
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// Calculate the end_ticks if a timeout is provided
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if (tval != NULL) {
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end_ticks = xTaskGetTickCount() + pdMS_TO_TICKS(tval->tv_sec * 1000 + tval->tv_usec / 1000);
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}
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// Preserve the original FD sets as select call will change them
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if (rfds) {
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o_rfds = *rfds;
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}
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if (wfds) {
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o_wfds = *wfds;
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}
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if (efds) {
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o_efds = *efds;
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}
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while (1) {
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// Restore original FD sets before the select call
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if (rfds) {
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*rfds = o_rfds;
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}
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if (wfds) {
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*wfds = o_wfds;
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}
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if (efds) {
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*efds = o_efds;
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}
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// Call select with a zero timeout to avoid blocking
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struct timeval zero_tv = {0, 0};
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int ret = s_real_select(fd, rfds, wfds, efds, &zero_tv);
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// Return on success
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if (ret > 0) {
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return ret;
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}
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// Return on any error except EINTR
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if (ret == -1 && errno != EINTR) {
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return ret;
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}
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/**
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* Sleep for maximum 10 tick(s) to allow other tasks to run.
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* This can be any value greater than zero.
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* 10 is a good trade-off between CPU time usage and timeout resolution.
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*/
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const TickType_t max_sleep_ticks = 10;
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TickType_t sleep_ticks = max_sleep_ticks;
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if (tval != NULL) {
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TickType_t now_ticks = xTaskGetTickCount();
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if (now_ticks >= end_ticks) {
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errno = 0;
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return 0;
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}
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// Sleep for the remaining time or a maximum of 10 tick
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TickType_t remaining_ticks = end_ticks - now_ticks;
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sleep_ticks = (remaining_ticks < max_sleep_ticks) ? remaining_ticks : max_sleep_ticks;
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}
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vTaskDelay(sleep_ticks);
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}
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}
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