PHP about PKCS7 signature verification. Workaround

PHP about PKCS7 signature verification.
The message you want to sign so, recipient can be sure it is you
Sent it
$data = << <>

You had my authorization to spend in dinner expenses.

The CEO
EOD;
Save message to File
$fp = fopen ("Msg.txt", "w");
Fwrite ($fp, $data);
Fclose ($FP);
Encrypt it
if (Openssl_pkcs7_sign ("Msg.txt", "Signed.txt", "Mycert.pem",
Array ("File://mycert.pem", "Mypassphrase"),
Array ("to" and "=" [email protected] ",//keyed syntax
"From:hq <[email protected]>",//indexed syntax
"Subject" = "Eyes only")
)) {
Message signed-send It!
EXEC (Ini_get ("Sendmail_path"). "< Signed.txt");
}
?>
Using this function to do the signature, involving the file read and write, may involve the high concurrency of the file, what is the best way to handle PHP?
The point is, I just need to pass the original data need to be signed $data, and this function every time the original data $data saved to the file, and then do the signature, and finally the string generated after the signature saved to Signed.txt, in practice this will certainly trigger the file operation problem, how to solve it?

------Solution--------------------
Do not use the same file name, you can use MD5 (UNIQID). ". TXT "as the file name for Msg.txt and Signed.txt.

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