Getting a Job Number in VS .NET

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The next three programs show three individual job management functions These functions are all included in a single source file, JobMgtc The first, Program 6-4, shows the GetJobNumber function Notice the use of file locking with a completion handler to unlock the file This technique protects against exceptions and inadvertent transfers around the unlock call Such a transfer might be inserted accidentally during code maintenance even if the original program is correct Also notice how the record past the end of the file is locked in the event that the file needs to be expanded with a new record
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Program 6-4 JobMgt: Creating New Job Information
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/* Job management utility function */ #include "EvryThngh" #include "JobMgth" /* Listed in Appendix A */ void GetJobMgtFileName (LPTSTR); LONG GetJobNumber (PROCESS_INFORMATION *pProcessInfo, LPCTSTR Command) /* Create a job number for the new process, and enter the new process information into the job database */ { HANDLE hJobData, hProcess; JM_JOB JobRecord; DWORD JobNumber = 0, nXfer, ExitCode, FsLow, FsHigh; TCHAR JobMgtFileName [MAX_PATH]; OVERLAPPED RegionStart; if (!GetJobMgtFileName (JobMgtFileName)) return -1; /* Produces "\tmp\UserNameJobMgt" */ hJobData = CreateFile (JobMgtFileName, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL); if (hJobData == INVALID_HANDLE_VALUE) return -1; /* Lock the entire file plus one possible new record for exclusive access */ RegionStartOffset = 0; RegionStartOffsetHigh = 0; RegionStarthEvent = (HANDLE)0; FsLow = GetFileSize (hJobData, &FsHigh); LockFileEx (hJobData, LOCKFILE_EXCLUSIVE_LOCK, 0, FsLow + SJM_JOB, 0, &RegionStart); __try { /* Read records to find empty slot */
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while (ReadFile (hJobData, &JobRecord, SJM_JOB, &nXfer, NULL) && (nXfer > 0)) { if (JobRecordProcessId == 0) break; hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, JobRecordProcessId); if (hProcess == NULL) break; if (GetExitCodeProcess (hProcess, &ExitCode) && (ExitCode != STILL_ACTIVE)) break; JobNumber++; } /* Either an empty slot has been found, or we are at end of file and need to create a new one */ if (nXfer != 0) /* Not at end of file Back up */ SetFilePointer (hJobData, -(LONG)SJM_JOB, NULL, FILE_CURRENT); JobRecordProcessId = pProcessInfo->dwProcessId; _tcsnccpy (JobRecordCommandLine, Command, MAX_PATH); WriteFile (hJobData, &JobRecord, SJM_JOB, &nXfer, NULL); } /* End try */ __finally { UnlockFileEx (hJobData, 0, FsLow + SJM_JOB, 0, &RegionStart); CloseHandle (hJobData); } return JobNumber + 1; }
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Program 6-5 shows the DisplayJobs job management function
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Program 6-5 JobMgt: Displaying Active Jobs
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BOOL DisplayJobs (void) /* Scan the job database file, reporting job status */ { HANDLE hJobData, hProcess; JM_JOB JobRecord; DWORD JobNumber = 0, nXfer, ExitCode, FsLow, FsHigh; TCHAR JobMgtFileName [MAX_PATH]; OVERLAPPED RegionStart; GetJobMgtFileName (JobMgtFileName); hJobData = CreateFile (JobMgtFileName, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL); RegionStartOffset = 0; RegionStartOffsetHigh = 0; RegionStarthEvent = (HANDLE)0; FsLow = GetFileSize (hJobData, &FsHigh);
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LockFileEx (hJobData, LOCKFILE_EXCLUSIVE_LOCK, 0, FsLow, FsHigh, &RegionStart); __try { while (ReadFile (hJobData, &JobRecord, SJM_JOB, &nXfer, NULL) && (nXfer > 0)){ JobNumber++; if (JobRecordProcessId == 0) continue; hProcess = OpenProcess (PROCESS_ALL_ACCESS, FALSE, JobRecordProcessId); if (hProcess != NULL) GetExitCodeProcess (hProcess, &ExitCode); _tprintf (_T (" [%d] "), JobNumber); if (hProcess == NULL) _tprintf (_T (" Done")); else if (ExitCode != STILL_ACTIVE) _tprintf (_T ("+ Done")); else _tprintf (_T (" ")); _tprintf (_T (" %s\n"), JobRecordCommandLine); /* Remove processes that are no longer in system */ if (hProcess == NULL) { /* Back up one record */ SetFilePointer (hJobData, -(LONG)nXfer, NULL, FILE_CURRENT); JobRecordProcessId = 0; WriteFile (hJobData, &JobRecord, SJM_JOB, &nXfer, NULL); } } /* End of while */ } /* End of __try */ __finally { UnlockFileEx (hJobData, 0, FsLow, FsHigh, &RegionStart); CloseHandle (hJobData); } return TRUE; }
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Program 6-6 shows the final job management function, FindProcessId, which obtains the process ID of a specified job number The process ID, in turn, can be used by the calling program to obtain a handle and other process status information
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Program 6-6 JobMgt: Getting the Process ID from a Job Number
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DWORD FindProcessId (DWORD JobNumber) /* Obtain the process ID of the specified job number */ { HANDLE hJobData; JM_JOB JobRecord; DWORD nXfer; TCHAR JobMgtFileName [MAX_PATH];
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OVERLAPPED RegionStart; /* Open the job management file */ GetJobMgtFileName (JobMgtFileName); hJobData = CreateFile (JobMgtFileName, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL); if (hJobData == INVALID_HANDLE_VALUE) return 0; /* Position to the entry for the specified job number * The full program assures that JobNumber is in range */ SetFilePointer (hJobData, SJM_JOB * (JobNumber - 1), NULL, FILE_BEGIN); /* Lock and read the record */ RegionStartOffset = SJM_JOB * (JobNumber - 1); RegionStartOffsetHigh = 0; /* Assume a "short" file */ RegionStarthEvent = (HANDLE)0; LockFileEx (hJobData, 0, 0, SJM_JOB, 0, &RegionStart); ReadFile (hJobData, &JobRecord, SJM_JOB, &nXfer, NULL); UnlockFileEx (hJobData, 0, SJM_JOB, 0, &RegionStart); CloseHandle (hJobData); return JobRecordProcessId; }
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