Signalsafe data structures Post: 302580087

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Top Forums Programming Signalsafe data structures Post 302580087 by Corona688 on Wednesday 7th of December 2011 12:18:56 PM

12-07-2011

Registered User

Working on it. It's harder than it sounds to guarantee order AND guarantee safety.

---------- Post updated at 11:18 AM ---------- Previous update was at 11:09 AM ----------

How about this:

Code:

#define SIGBUF_SIZE 1024

struct
{
        unsigned int rdpos, wrpos;
        int buffer[SIGBUF_SIZE];
} sigbuf={ 0, 0 };

int put_value(int val)
{
        unsigned int wrpos=__sync_fetch_and_add(&sigbuf.wrpos, 1);
        unsigned int rdpos=__sync_fetch_and_add(&sigbuf.rdpos, 0);
        // Compare this way, to prevent integer wraparound problems!
        unsigned int off=(wrpos-rdpos);

        if(off >= SIGBUF_SIZE)
        {
                __sync_fetch_and_sub(&sigbuf.wrpos, 1);
                return(-1);
        }

        sigbuf.buffer[wrpos % SIGBUF_SIZE]=val;
        return(0);
}

int get_value(void)
{
        unsigned int wrpos=__sync_fetch_and_add(&sigbuf.wrpos, 0);
        // Do NOT add here!  If a signal happens, it may see a 'free'
        // element even though there's not.  Only add once we're sure
        // there's anything to read.
        unsigned int rdpos=__sync_fetch_and_add(&sigbuf.rdpos, 0);
        unsigned int off=(wrpos-rdpos);

        if(off == 0)    // Empty buffer
                return(-1);

        return(sigbuf.buffer[__sync_fetch_and_add(&sigbuf.rdpos, 1)%SIGBUF_SIZE]);
}

basically, rdpos and wrpos get incremented without limit, and % SIGBUF_SIZE is used to wrap their values to inside the array. We do 'unsigned int off=(wrpos-rdpos)' instead of just comparing rdpos and wrpos because, if it hits integer wraparound, rdpos might be near INT_MAX while rdpos is practically zero. Subtracting gets rid of the wraparound.

You shouldn't call get_value in a signal handler, but put_value ought to be safe.

Corona688

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rsa_sign_asn1_octet_string

RSA_sign_ASN1_OCTET_STRING(3SSL)				      OpenSSL					  RSA_sign_ASN1_OCTET_STRING(3SSL)

NAME

       RSA_sign_ASN1_OCTET_STRING, RSA_verify_ASN1_OCTET_STRING - RSA signatures

SYNOPSIS

	#include <openssl/rsa.h>

	int RSA_sign_ASN1_OCTET_STRING(int dummy, unsigned char *m,
	   unsigned int m_len, unsigned char *sigret, unsigned int *siglen,
	   RSA *rsa);

	int RSA_verify_ASN1_OCTET_STRING(int dummy, unsigned char *m,
	   unsigned int m_len, unsigned char *sigbuf, unsigned int siglen,
	   RSA *rsa);

DESCRIPTION

       RSA_sign_ASN1_OCTET_STRING() signs the octet string m of size m_len using the private key rsa represented in DER using PKCS #1 padding. It
       stores the signature in sigret and the signature size in siglen. sigret must point to RSA_size(rsa) bytes of memory.

       dummy is ignored.

       The random number generator must be seeded prior to calling RSA_sign_ASN1_OCTET_STRING().

       RSA_verify_ASN1_OCTET_STRING() verifies that the signature sigbuf of size siglen is the DER representation of a given octet string m of
       size m_len. dummy is ignored. rsa is the signer's public key.

RETURN VALUES

       RSA_sign_ASN1_OCTET_STRING() returns 1 on success, 0 otherwise.	RSA_verify_ASN1_OCTET_STRING() returns 1 on successful verification, 0
       otherwise.

       The error codes can be obtained by ERR_get_error(3).

BUGS

       These functions serve no recognizable purpose.

SEE ALSO

       ERR_get_error(3), objects(3), rand(3), rsa(3), RSA_sign(3), RSA_verify(3)

HISTORY

       RSA_sign_ASN1_OCTET_STRING() and RSA_verify_ASN1_OCTET_STRING() were added in SSLeay 0.8.

1.0.0e								    2002-09-25					  RSA_sign_ASN1_OCTET_STRING(3SSL)