【llbc】App运行时能力扩充 - 只允许启动一个实例 #224#378
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January 22, 2025 10:28
This reverts commit 71e2a5e.
lailongwei
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win32平台实现还有一些细节问题，可以再修改一波，另：建议整体review一下哈 @faith-free1st
| static char runningExeFilePath[MAX_PATH + 1] = {0}; | ||
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| // Get current execute file path. | ||
| LLBC_String selfExeFilePath = LLBC_Directory::ModuleFilePath(); |
| NULL); | ||
| LLBC_SetErrAndReturnIf(exclusiveInfoFile == INVALID_HANDLE_VALUE, LLBC_ERROR_OSAPI, LLBC_FAILED); | ||
| LLBC_Defer( | ||
| LLBC_SetErrAndReturnIf(!CloseHandle(exclusiveInfoFile), LLBC_ERROR_OSAPI,) |
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此处是defer语句，无需再set error and return if, 直接CloseHandle()即可
| : exclusiveInfoFilePath; | ||
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| // Create then read-lock exclusive info file. | ||
| HANDLE exclusiveInfoFile = CreateFileA(nmlExclusiveInfoFilePath.c_str(), |
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windows操作系统api是大驼峰风格，容易跟框架混淆，建议加'::'
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| // Read pid from exclusive info file. | ||
| DWORD fileSize = GetFileSize(exclusiveInfoFile, NULL); | ||
| LLBC_SetErrAndReturnIf(fileSize == -1 || fileSize >= 32, LLBC_ERROR_OSAPI, LLBC_FAILED); |
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未细致考虑：几处问题：
- 返回 -1 是失败的判断，不符合api规范，建议用
INVALID_FILE_SIZE来判断 fileSize >= 32是一个“业务测认为的错误”，在这种情况下，win32 api ::GetLastError()返回的值是错误或不确定的，因为OS API并未失败，这里粗心了，未区分这个case就统一以LLBC_ERROR_OSAPI方式的错误来做GetFileSize()时，如果大小大于32位大小，会将高位设置到第二个参数，我们使用时还很复杂，建议使用GetFileSizeEx()代替，详细api说明（下方也有截图）：https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfilesize
| exclusiveInfoBuf[fileSize] = '\0'; | ||
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| // Deal with exclusive info. | ||
| long exclusiveInfoPid = LLBC_Str2Long(exclusiveInfoBuf); |
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long在windows msvc的64位模式下编译是32位大小，有歧义（int/long是可以给编译器做决定的，而msvc遵循32位规范来，就是这样奇葩），建议使用int64
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| // Deal with exclusive info. | ||
| long exclusiveInfoPid = LLBC_Str2Long(exclusiveInfoBuf); | ||
| LLBC_ReturnIf(exclusiveInfoPid == getpid(), LLBC_FAILED); |
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这里直接返回错误，未设置任何errorno，不符合框架规范：框架api要求统一化设置错误码
| // Open executable process by pid. | ||
| HANDLE processHandle = OpenProcess( | ||
| PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, FALSE, exclusiveInfoPid); | ||
| if (processHandle != NULL) |
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OpenProcess()应该会返回很多很多种可能性的错误，是否需要针对性处理，而不是统一处理（==null时）
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这里没有对processHandle为NULL的情况做处理主要两点原因：
1、processHandle在一些情况下为NULL是合理的，比如之前运行的进程已经结束了。
2、这里是NULL不会影响后续逻辑，打印一条日志容易产生误会
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可选方案
1、文件锁
优点：
标准化实现，可拓展
tip:目录+pid保证原子性，检查/proc//exe来保证进程指向验证
缺点：
crash之后需要额外处理(llbc不做处理，在进程启动的时候会检查并清理文件内容)
2、POSIX named semaphores
优点：
实现简单，原子性保证
缺点：
具有内核生命周期，系统重启前都无法被清理
3、bind a port
优点：
进程关闭后内核会自动关闭文件描述符，简单
如果进程本身就已经绑定了一个port，那完全无需改动
缺点：
对于不需要绑定port的进程也需要绑定port
port是系统资源，对于运行多个程序的系统，依赖单一的port不太可控
文件描述符会传递给子进程
依赖网络功能
4、mutex in shared memory
优点：
基于共享内存，原子性保证
缺点：
crash之后需要额外处理
方案选取
方案2，4在crash之后都会有数据残留且难以清除的问题。
接下来是在方案1和3里面选，两个方案其实都是操作系统提供的支持，一个是文件模块，一个是网络模块。
考虑到网络模块是对外模块，采用使用文件模块的方案一更稳定一些，最终决定使用方案一
功能实现
在Mac和Linux下：
1、判断.pid文件是否存在，存在就读取pid判断是否同名进程运行中。不存在则创建文件并直接进入下一步
2、设置.pid文件锁，写入当前进程pid到.pid文件中，释放文件锁
在Win平台下，步骤2中的设置文件锁，可以通过设置CreateFileA接口参数中的dwShareMode参数为共享读FILE_SHARE_READ只来实现。