Closed Bug 26506 Opened 20 years ago Closed 20 years ago
The DNS lock is not needed with native threads
In prnetdb.c, there is a DNS lock that we hold while copying the result of gethostbyname (and its cousins getipnodebyname or gethostbyname2) to our result buffer. This is because traditionally, gethostbyname returns its result in a static buffer. There are two ways to avoid this DNS lock. 1. Use the (non-standard) reentrant version of gethostbyname, gethostbyname_r. 2. If native threads are used and gethostbyname returns its result in a thread-specific data buffer (required by pthreads or some other POSIX or Unix standard), the result won't be overwritten by other threads' gethostbyname calls. For these two cases, we should define LOCK_DNS() and UNLOCK_DNS() to be null macros.
I checked some common Unix flavors. Here is the result. 1. There are at least three flavors of gethostbyname_r. 2. Only OSF1 V4.0D, HP-UX 11.00, and AIX 4.3 have a thread-safe gethostbyname() function that returns its result in thread-specific storage. Error code is returned in the thread-specific h_errno on failure. The reentrant gethostbyname_r function on these platforms is deprecated and new code is advised to use the thread-safe gethostbyname function. 3. Solaris 2.5.1 - 8 and IRIX 6.5 (but not IRIX 6.3) have gethostbyname_r with this function prototype: struct hostent *gethostbyname_r( const char *name, struct hostent *result, char *buffer, int buflen, int *h_errnop); If the buffer is too small, errno is set to ERANGE. Otherwise, error code is returned in *h_errnop on failure. Note that the gethostbyname(3NSL) man page on Solaris 8 says the following in the "WARNINGS" section: The reentrant interfaces gethostbyname_r(), gethostbyaddr_r(), and gethostent_r() are included in this release on an uncommitted basis only, and are subject to change or removal in future minor releases. But the gethostbyname(3N) man page on Solaris 2.5.1 says the same thing. 4. RedHat Linux 6.0 and 6.1 have a gethostbyname_r function that works but is not documented. It has a different function prototype: int gethostbyname_r( const char *name, struct hostent *result_buf, char *buf, size_t buflen, struct hostent **result, int *h_errnop); Is it worth the trouble to use gethostbyname_r on Solaris, IRIX, and Linux, in light of the warning in the Solaris man page and the fact that it is not documented on Linux?
One thing that's easy to fix: the getipnodebyname and getipnodebyaddr functions of RFC 2553 are thread safe, so it's not necessary to lock around them. /cvsroot/mozilla/nsprpub/pr/src/misc/prnetdb.c, revision 3.15
The proposed patch (id=9114) introduced the following new configuration macros: 1. _PR_HAVE_THREADSAFE_GETHOST: define this macro if the gethostbyXXX functions return the result in thread-specific storage. E.g., AIX, HP-UX, and OSF1. 2. _PR_HAVE_GETHOST_R: define this macro if the platform has the reentrant gethostbyXXX_r functions. See the next two macros. 3. _PR_HAVE_GETHOST_R_POINTER: define this macro if the gethostbyXXX_r functions return a struct hostent* pointer. E.g., IRIX and Solaris. 4. _PR_HAVE_GETHOST_R_INT: define this macro if the gethostbyXXX_r functions return an int. E.g., Linux glibc. We don't need to use the DNS lock if _PR_HAVE_THREADSAFE_GETHOST or _PR_HAVE_GETHOST_R is defined. I've only checked the six Unix flavors mentioned above. Other Unix flavors still need to be checked. I checked in the patch on the main trunk. /cvsroot/mozilla/nsprpub/config/AIX.mk, revision 3.8 /cvsroot/mozilla/nsprpub/config/HP-UX.mk, revision 3.9 /cvsroot/mozilla/nsprpub/config/IRIX.mk, revision 3.11 /cvsroot/mozilla/nsprpub/config/OSF1.mk, revision 3.11 /cvsroot/mozilla/nsprpub/pr/include/md/_linux.h, revision 3.27 /cvsroot/mozilla/nsprpub/pr/include/md/_solaris.h, revision 3.13 /cvsroot/mozilla/nsprpub/pr/src/misc/prnetdb.c, revision 3.17 Gordon, the best way to test this patch is to check out the tip of mozilla/nsprpub.
It turns out that the gethostbyXXX_r functions in glibc on Linux are documented in 'info libc'; they are just not documented in the man pages. On a RedHat Linux 6.1 machine, fire up 'info libc', press 's' (to search for string), and type 'gethostbyname_r'.
Marked the bug fixed. Note that the fix was only checked in on the tip of NSPR. Because Mozilla is pulling the NSPRPUB_CLIENT_BRANCH of NSPR, it is not picking up this fix right now.
Status: ASSIGNED → RESOLVED
Closed: 20 years ago
Resolution: --- → FIXED
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