Tasker与Pydroid文件共享冲突致崩溃，如何检测文件占用并等待？

问题背景 #

用Tasker和Pydroid开发手机图像识别应用：Tasker每5秒截取屏幕保存，同时读取结果文件展示最新分析结果；Pydroid打开截图分析后，将结果写入文本文件供Tasker读取。但当其中一个应用占用文件时，另一个应用尝试访问会导致手机崩溃重启，需要在两端实现文件占用检测与等待机制。

当前Tasker任务代码 #

A1: Flash [
         Text: Enabled
         Continue Task Immediately: On
         Dismiss On Click: On ]
    
    A2: Variable Set [
         Name: %Enabled
         To: True
         Max Rounding Digits: 3
         Structure Output (JSON, etc): On ]
    
    A3: Take Screenshot [
         File: /storage/47BE-16F5/folder/screenshot.png ]
    
    A4: Read File [
         File: /storage/47BE-16F5/folder/text.txt
         To Var: %text
         Structure Output (JSON, etc): On ]
    
    A5: Flash [
         Text: %text
         Continue Task Immediately: On
         Dismiss On Click: On ]
    
    A6: Wait [
         MS: 0
         Seconds: 5
         Minutes: 0
         Hours: 0
         Days: 0 ]
    
    A7: Goto [
         Type: Action Number
         Number: 3 ]
        If [ %Enabled eq True ]

当前Python代码 #

from PIL import Image

screenshot = Image.open("/storage/47BE-16F5/folder/screenshot.png")
...
with open(TEXT_DIR, 'w', encoding="utf-8") as f:
    f.write(results)

解决方案 #

Tasker端优化 #

1. 给文件操作添加重试机制
   在截图和读文件操作前加入循环重试，遇到错误时等待1秒后再次尝试，最多重试3次：

   • 修改截图步骤（A3）：

     A3: For [ Variable: %retry Items: 1,2,3 ]
         A3.1: Take Screenshot [ File: /storage/47BE-16F5/folder/screenshot.png ]
         A3.2: If [ %err Set ]
             A3.3: Wait [ Seconds: 1 ]
             A3.4: Continue Loop
         A3.5: Else
             A3.6: Break Loop
         A3.7: End If
     

   • 修改读文件步骤（A4）：

     A4: For [ Variable: %retry Items: 1,2,3 ]
         A4.1: Read File [ File: /storage/47BE-16F5/folder/text.txt To Var: %text ]
         A4.2: If [ %err Set ]
             A4.3: Wait [ Seconds: 1 ]
             A4.4: Continue Loop
         A4.5: Else
             A4.6: Break Loop
         A4.7: End If
     

2. 用临时文件替换原文件，减少占用时间
   截图先保存到临时文件，再原子替换目标文件，避免Pydroid读取到半写入的截图：

   A3: Take Screenshot [ File: /storage/47BE-16F5/folder/screenshot_temp.png ]
   A3.1: Move/Copy File [ From: /storage/47BE-16F5/folder/screenshot_temp.png To: /storage/47BE-16F5/folder/screenshot.png Replace: On ]
   

Pydroid端优化 #

1. 实现带重试的安全文件读写函数
   替换直接打开文件的代码，用循环尝试访问，直到成功或达到重试上限，避免因文件占用直接崩溃：

   import time
   from PIL import Image
   
   def safe_open_image(file_path, max_retries=5, delay=1):
       for _ in range(max_retries):
           try:
               # 以只读模式打开，降低锁冲突概率
               return Image.open(file_path, mode='r')
           except Exception:
               time.sleep(delay)
       raise RuntimeError(f"无法打开截图文件，重试{max_retries}次后失败")
   
   # 安全打开截图
   screenshot = safe_open_image("/storage/47BE-16F5/folder/screenshot.png")
   try:
       # 图像分析逻辑...
       results = "分析结果"
   finally:
       # 确保图片对象关闭，释放文件句柄
       screenshot.close()
   
   def safe_write_file(file_path, content, max_retries=5, delay=1):
       for _ in range(max_retries):
           try:
               with open(file_path, 'w', encoding="utf-8") as f:
                   f.write(content)
               return
           except Exception:
               time.sleep(delay)
       raise RuntimeError(f"无法写入结果文件，重试{max_retries}次后失败")
   
   # 安全写入分析结果
   safe_write_file(TEXT_DIR, results)
   

2. 及时释放文件句柄
   用try-finally包裹图片处理逻辑，确保分析完成后立即关闭图片对象，释放文件锁，减少Tasker访问时的冲突概率。

内容的提问来源于stack exchange，提问作者alwaysintrouble