Differences
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file_exists_considered_harmful [2013/01/14 13:41] sparre created - with open-or-create example |
file_exists_considered_harmful [2013/01/16 08:24] (current) sparre Read to end of file example |
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| Line 23: | Line 23: | ||
| Mode => Append_File); | Mode => Append_File); | ||
| end Open_Or_Create;</code> | end Open_Or_Create;</code> | ||
| + | |||
| + | ====== Similar file system race conditions ====== | ||
| + | |||
| + | Not only "Ada.Directories.Exists" is dangerous and a possible source of race conditions. Other functions checking the state of the file system should also be used with care. Below are a few (so far only one) examples. | ||
| + | |||
| + | ===== Read to end of file ===== | ||
| + | |||
| + | This procedure will read every line in a text file and send it to processing until it reaches the end of the file. Then it will close the file. Even if our loop checked ''End_Of_File (File)'' before calling "Get_Line (File)", we would still have to handle exception End_Error, as another process/task might change the contents/size of the file in parallel with this procedure. | ||
| + | |||
| + | <code Ada>type Processor is access procedure (Item : in String); | ||
| + | |||
| + | procedure Process (File : in out File_Type; | ||
| + | Line_Handler : in Processor) is | ||
| + | begin | ||
| + | loop | ||
| + | Line_Handler (Get_Line (File)); | ||
| + | end loop; | ||
| + | exception | ||
| + | when End_Error => | ||
| + | Close (File); | ||
| + | when others => | ||
| + | raise; | ||
| + | end Process;</code> | ||
