您如何在Windows下共享日志文件？

Question

我有几个不同的过程，我希望它们全部记录到同一个文件中。这些进程在Windows 7系统上运行。有些是python脚本，有些是cmd批处理文件。

在Unix下，您只需让所有人以附加模式打开文件并注销即可。只要每个进程PIPE_BUF在单个消息中写入的字节数少于字节，write就可以确保每个调用都不会交叉。

有没有办法在Windows下实现这一目标？像Unix这样幼稚的方法失败了，因为Windows不喜欢一个以上的进程，默认情况下一次打开一个文件进行写入。

Answer 1

可能有多个批处理过程安全地写入单个日志文件。我对Python一无所知，但我想这个答案中的概念可以与Python集成在一起。

Windows最多允许一个进程在任何时间点打开一个特定文件以进行写访问。这可用于实现基于文件的锁定机制，以确保事件在多个进程之间被序列化。有关某些示例，请参见http://www.dostips.com/forum/viewtopic.php?p=12454。

由于您要做的只是写入日志，因此可以将日志文件本身用作锁。日志操作封装在一个子例程中，该子例程尝试以附加模式打开日志文件。如果打开失败，例程将循环返回并重试。一旦打开成功，日志将被写入然后关闭，然后例程返回到调用方。该例程执行传递给它的任何命令，并将例程中写入stdout的所有内容重定向到日志。

这是一个测试批处理脚本，它创建5个子进程，每个子进程写入日志文件20次。写入被安全地交错。

@echo off
setlocal
if "%~1" neq "" goto :test

:: Initialize
set log="myLog.log"
2>nul del %log%
2>nul del "test*.marker"
set procCount=5
set testCount=10

:: Launch %procCount% processes that write to the same log
for /l %%n in (1 1 %procCount%) do start "" /b "%~f0" %%n

:wait for child processes to finish
2>nul dir /b "test*.marker" | find /c "test" | >nul findstr /x "%procCount%" || goto :wait

:: Verify log results
for /l %%n in (1 1 %procCount%) do (
  <nul set /p "=Proc %%n log count = "
  find /c "Proc %%n: " <%log%
)

:: Cleanup
del "test*.marker"
exit /b

==============================================================================
:: code below is the process that writes to the log file

:test
set instance=%1
for /l %%n in (1 1 %testCount%) do (
  call :log echo Proc %instance% says hello!
  call :log dir "%~f0"
)
echo done >"test%1.marker"
exit

:log command args...
2>nul (
  >>%log% (
    echo ***********************************************************
    echo Proc %instance%: %date% %time%
    %*
    (call ) %= This odd syntax guarantees the inner block ends with success  =%
            %= We only want to loop back and try again if redirection failed =%
  )
) || goto :log
exit /b

这是显示每个过程全部20次写入均成功的输出

Proc 1 log count = 20
Proc 2 log count = 20
Proc 3 log count = 20
Proc 4 log count = 20
Proc 5 log count = 20

您可以打开生成的“ myLog.log”文件，以查看如何安全地交错写入。但是输出太大，无法在此处发布。

可以很容易地证明，通过修改：log例程，来自多个进程的同时写入操作可能会失败，这样它就不会在失败时重试。

:log command args...
>>%log% (
  echo ***********************************************************
  echo Proc %instance%: %date% %time%
  %*
)
exit /b

这是“打破”：log例程后的一些示例结果

The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
The process cannot access the file because it is being used by another process.
Proc 1 log count = 12
Proc 2 log count = 16
Proc 3 log count = 13
Proc 4 log count = 18
Proc 5 log count = 14