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Atomic File Operations Using File Lock

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The file module has functions lock files across several operations that are almost exact equivalents to POSIX API functions; the primary difference is the advantage of valuable return error codes to the application.
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If a file is shared between several tasks in an application, the file lock can be employed to guarantee that a series of file operations are executed atomically. fs_flockfile() (or its non-blocking equivalent fs_ftrylockfile()) acquires the lock for a task (if it does not already own it). Accesses from other tasks will be blocked until fs_funlockfile() is called.

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Each file actually has a lock count associated with it. This allows nested calls by a task to acquire a file lock; each of those calls must be matched with a call to fs_funlockfile().

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FS_ERR *p_err); void FSFile_LockSet (FS_FILE *p_file, FS_ERR *p_err);

POSIX API Equivalent
void fs_flockfile (FS_FILE *file); int fs_ftrylockfile (FS_FILE *file); void fs_funlockfile (FS_FILE *file);
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void App_Fnct (void)

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File Module Function {

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void FSFile_LockGet (FS_FILE *p_file,
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unsigned char data1[50];

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FS_ERR *p_err)
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unsigned char data2[10];

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void FSFile_LockAccept (FS_FILE *p_file,
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if (App_FilePtr != (FS_FILE *)0) {

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fs_flockfile(App_FilePtr); /* Lock file. */

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/* See Note #1. */

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/* Wr data atomically. */

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fs_fwrite(data1, 1, sizeof(data1), App_FilePtr);

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fs_fwrite(data2, 1, sizeof(data1), App_FilePtr);

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fs_funlockfile(App_FilePtr); /* Unlock file. */

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}

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}

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      Example file lock usage
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        fs_flockfile() will block the calling task until the file is available. If the task must write to the file only if no other task is currently accessing it, the non-blocking function fs_funlockfile() can be used.