c++ 11 编译代码条件变量阻塞状态 wait失效

天岦 · 2024-10-22 21:20:39

基于全志T113-s3硬件平台，使用condition_variable 条件变量时候调用wait阻塞等待变量释放，但是再等待通知期间，cpu并不会释放，而是一直保持占用状态。难以理解。
以下是测试代码：

#include <iostream>
#include <thread>
#include <mutex>
#include <condition_variable>

std::mutex mtx;
std::condition_variable cond_not_empty_;
bool ready = false;

void wait_for_task() {
    std::unique_lock<std::mutex> lock(mtx);
    // 等待直到 ready 为 true
    cond_not_empty_.wait(lock, []{ return ready; });
    std::cout << "Task is ready, proceeding...\n";
}

void signal_task() {
    std::lock_guard<std::mutex> lock(mtx);
    ready = true;
    // 唤醒等待的线程
    cond_not_empty_.notify_one();
}

int main() {
    std::thread worker(wait_for_task);
    // 模拟其他工作
    std::this_thread::sleep_for(std::chrono::seconds(20));
    signal_task();  // 通知任务已准备好
    worker.join();
    return 0;
}

以下是执行完代码处理后得结果，主线程休眠装台0占用，worker线程占用cpu再25%：

天岦 · 2024-10-22 21:44:03

同样得代码再服务器上跑没啥问题，两个线程得占用都是0，奇奇怪怪得。

t113@t113-docker-1:~/t113/cpu_usage/build$ ./waitT &
[2] 9925
t113@t113-docker-1:~/t113/cpu_usage/build$ ./cpu_usage 9925
Analyzing CPU usage for program: waitT (PID: 9925)
TID	Thread_Name	CPU_Usage(%)
9925	waitT	0.00%
9926	waitT	0.00%
t113@t113-docker-1:~/t113/cpu_usage/build$ Task is ready, proceeding...

天岦 · 2024-10-23 00:55:48

感觉应该是编译器问题或者是我的linux线程调度问题，目前采用了一种十分呆瓜的方案，使用while循环，然后再循环中使用sleep来释放cpu,目前能够有效的降低线程中的cpu占用。但是问题依旧存在。

root@TinaLinux:~# ./cpu_usage 312
Analyzing CPU usage for program: main (PID: 312)
TID	Thread_Name	CPU_Usage(%)
312	main	0.00%
313	scan_key	0.00%
314	mount_check	0.00%
315	read_rs485	7.50%
316	din_interrupt	0.00%
317	addr_led_blink	0.00%
318	addr_led_blink	0.00%
319	mixing	0.00%
325	send_codec	30.00%
326	send_spdif	35.50%
root@TinaLinux:~# kill -9 312
root@TinaLinux:~# Killed
TXplayer has stopped. Restarting in 5 seconds...
TXplayer lost executable permission. Adding executable permission again...
Thread Name: main, TID: 332
[ 1542.112483] sw_uart_check_baudset()903 - uart1, baud 500000 beyond rance
Thread Name: mount_check, TID: 334
Thread Name: scan_key, TID: 333
Thread Name: mixing, TID: 339
Thread Name: addr_led_blink, TID: 337
Thread Name: read_rs485, TID: 335
Thread Name: din_interrupt, TID: 336
Thread Name: addr_led_blink, TID: 338
[ 1542.149690] [SNDCODEC][sunxi_card_hw_params][620]:stream_flag: 0
[ 1542.374365] sunxi-spdif 2036000.spdif: active: 1
Thread Name: send_codec, TID: 345
Thread Name: send_spdif, TID: 346
root@TinaLinux:~# ./cpu_usage 332
Analyzing CPU usage for program: main (PID: 332)
TID	Thread_Name	CPU_Usage(%)
332	main	0.00%
333	scan_key	0.00%
334	mount_check	0.00%
335	read_rs485	7.50%
336	din_interrupt	0.00%
337	addr_led_blink	0.00%
338	addr_led_blink	0.00%
339	mixing	0.00%
345	send_codec	0.00%
346	send_spdif	1.00%

天岦 · 2024-10-24 15:08:38

更换了交叉编译器，重新编译程序，CPU占用问题依旧没得到解决，目前推测应该是tina linux问题

天岦 · 2024-10-24 15:16:09

目前测试，证实确实是tina linux的问题导致的，更换镜像重新烧录后，执行wait线程挂起，cpu消耗为0，测试正常，目前已经修改了SDK重新编译系统（PS:来路不明的野SDK最好不要用，否则掉到坑里很难爬出来）

root@TinaLinux:~# ./xhl &
root@TinaLinux:~# top
Mem: 18828K used, 93844K free, 0K shrd, 1248K buff, 2716K cached
CPU:   0% usr   4% sys   0% nic  95% idle   0% io   0% irq   0% sirq
Load average: 0.00 0.00 0.00 1/55 225
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  223   150 root     S     1880   2%   0% ./xhl
  143     1 root     S     1312   1%   0% /bin/adbd -D
    1     0 root     S     1056   1%   0% /sbin/init
  150     1 root     S     1056   1%   0% -/bin/sh
  225   150 root     R     1056   1%   0% top
  141     1 root     S      696   1%   0% /sbin/swupdate-progress -w
   55     2 root     SW       0   0%   0% [spi0]
   10     2 root     IW       0   0%   0% [rcu_preempt]
   21     2 root     IW       0   0%   0% [kworker/1:1-ubi]
   53     2 root     IW       0   0%   0% [kworker/u4:1-ev]
    7     2 root     IW       0   0%   0% [kworker/u4:0-ev]
    5     2 root     IW       0   0%   0% [kworker/0:0-mm_]
   15     2 root     SW       0   0%   0% [ksoftirqd/1]
   73     2 root     IW       0   0%   0% [kworker/1:2-ubi]
   20     2 root     IW       0   0%   0% [kworker/0:1-ubi]
    9     2 root     SW       0   0%   0% [ksoftirqd/0]
  103     2 root     SW       0   0%   0% [ubifs_bgt0_7]
   16     2 root     IW       0   0%   0% [kworker/1:0-mm_]
   19     2 root     SW       0   0%   0% [rcu_tasks_kthre]
^C 17     2 root     IW<      0   0%   0% [kworker/1:0H-kb]
root@TinaLinux:~# ./cpu_usage 223
Analyzing CPU usage for program: xhl (PID: 223)
TID	Thread_Name	CPU_Usage(%)
223	xhl	0.00%
224	xhl	0.00%
root@TinaLinux:~# Task is ready, proceeding...

最近编辑记录天岦 (2024-10-24 15:16:30)

天岦 · 2024-10-24 15:44:22

海石生风说：

既然怀疑编译器。那它啥版本？哪来的？换过编译器没有？

代码验证没有问题，接下来当然就是排查编译器和系统问题咯，就是换过编译器了，才有下面的系统问题排查

WhyCan Forum(哇酷开发者社区)

楼主 # 2024-10-22 21:20:39 分享评论