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1997-08-10 19:17 Philip Blundell <Philip.Blundell@pobox.com> * nss/nss_db/db-XXX.c: Include <db_185.h> not <db.h>. Somebody should update this to use the new db API. * nss/nss_db/db-netgrp.c: Likewise. * nss/nss_db/db-alias.c: Likewise. * db2/Makefile: Makefile for db-2.x in glibc. 1997-08-27 21:20 Ulrich Drepper <drepper@cygnus.com> * csu/Makefile (before-compile): New goal. Make sure abi-tag.h is generated. [$(elf)=yes] (asm-CPPFLAGS): Make sure abi-tag.h file can be found. * Makeconfig [$(build-omitfp)=yes] (CFLAGS-.o): Add -D__USE_STRING_INLINES. * string/string.f: Move strnlen optimization after inclusion of <bits/string.h>. Include <bits/string.h> only if __USE_STRING_INLINES is defined. * sysdeps/generic/memcpy.c: Undef memcpy to allow macro of this name in <bits/string.h>. * sysdeps/generic/memset.c: Likewise. * sysdeps/i386/string.h: i386 optimized string functions. * sysdeps/i386/i486string.h: i486+ optimized string functions. * Makefile (subdirs): Change db to db2. * shlib-versions: Bump libdb verion number to 3. * include/db.h: Include from db2 directory. * include/db_185.h: New file. * sysdeps/i386/Makefile [$(subdirs)=db2] (CPPFLAGS): Add macros to provide spinlock information for db2. * sysdeps/m68k/m68020/Makefile: New file. Likewise. * sysdeps/sparc/Makefile: New file. Likewise. * sysdeps/unix/sysv/linux/Makefile [$(subdirs)=db2] (CPPFLAGS): Add -DHAVE_LLSEEK. * db2/config.h: Hand-edited config file for db2 in glibc. * db2/compat.h: New file from db-2.3.4. * db2/db.h: Likewise. * db2/db_185.h: Likewise. * db2/db_int.h: Likewise. * db2/makedb.c: Likewise. * db2/btree/bt_close.c: Likewise. * db2/btree/bt_compare.c: Likewise. * db2/btree/bt_conv.c: Likewise. * db2/btree/bt_cursor.c: Likewise. * db2/btree/bt_delete.c: Likewise. * db2/btree/bt_open.c: Likewise. * db2/btree/bt_page.c: Likewise. * db2/btree/bt_put.c: Likewise. * db2/btree/bt_rec.c: Likewise. * db2/btree/bt_recno.c: Likewise. * db2/btree/btree_auto.c: Likewise. * db2/btree/bt_rsearch.c: Likewise. * db2/btree/bt_search.c: Likewise. * db2/btree/bt_split.c: Likewise. * db2/btree/bt_stat.c: Likewise. * db2/btree/btree.src: Likewise. * db2/common/db_appinit.c: Likewise. * db2/common/db_err.c: Likewise. * db2/common/db_byteorder.c: Likewise. * db2/common/db_apprec.c: Likewise. * db2/common/db_salloc.c: Likewise. * db2/common/db_log2.c: Likewise. * db2/common/db_region.c: Likewise. * db2/common/db_shash.c: Likewise. * db2/db/db.c: Likewise. * db2/db/db.src: Likewise. * db2/db/db_conv.c: Likewise. * db2/db/db_dispatch.c: Likewise. * db2/db/db_dup.c: Likewise. * db2/db/db_overflow.c: Likewise. * db2/db/db_pr.c: Likewise. * db2/db/db_rec.c: Likewise. * db2/db/db_ret.c: Likewise. * db2/db/db_thread.c: Likewise. * db2/db/db_auto.c: Likewise. * db2/db185/db185.c: Likewise. * db2/db185/db185_int.h: Likewise. * db2/dbm/dbm.c: Likewise. * db2/hash/hash.c: Likewise. * db2/hash/hash.src: Likewise. * db2/hash/hash_page.c: Likewise. * db2/hash/hash_conv.c: Likewise. * db2/hash/hash_debug.c: Likewise. * db2/hash/hash_stat.c: Likewise. * db2/hash/hash_rec.c: Likewise. * db2/hash/hash_dup.c: Likewise. * db2/hash/hash_func.c: Likewise. * db2/hash/hash_auto.c: Likewise. * db2/include/mp.h: Likewise. * db2/include/btree.h: Likewise. * db2/include/db.h.src: Likewise. * db2/include/db_int.h.src: Likewise. * db2/include/db_shash.h: Likewise. * db2/include/db_swap.h: Likewise. * db2/include/db_185.h.src: Likewise. * db2/include/txn.h: Likewise. * db2/include/db_am.h: Likewise. * db2/include/shqueue.h: Likewise. * db2/include/hash.h: Likewise. * db2/include/db_dispatch.h: Likewise. * db2/include/lock.h: Likewise. * db2/include/db_page.h: Likewise. * db2/include/log.h: Likewise. * db2/include/db_auto.h: Likewise. * db2/include/btree_auto.h: Likewise. * db2/include/hash_auto.h: Likewise. * db2/include/log_auto.h: Likewise. * db2/include/txn_auto.h: Likewise. * db2/include/db_ext.h: Likewise. * db2/include/btree_ext.h: Likewise. * db2/include/clib_ext.h: Likewise. * db2/include/common_ext.h: Likewise. * db2/include/hash_ext.h: Likewise. * db2/include/lock_ext.h: Likewise. * db2/include/log_ext.h: Likewise. * db2/include/mp_ext.h: Likewise. * db2/include/mutex_ext.h: Likewise. * db2/include/os_ext.h: Likewise. * db2/include/txn_ext.h: Likewise. * db2/include/cxx_int.h: Likewise. * db2/include/db_cxx.h: Likewise. * db2/include/queue.h: Likewise. * db2/lock/lock.c: Likewise. * db2/lock/lock_conflict.c: Likewise. * db2/lock/lock_util.c: Likewise. * db2/lock/lock_deadlock.c: Likewise. * db2/log/log.c: Likewise. * db2/log/log_get.c: Likewise. * db2/log/log.src: Likewise. * db2/log/log_compare.c: Likewise. * db2/log/log_put.c: Likewise. * db2/log/log_rec.c: Likewise. * db2/log/log_archive.c: Likewise. * db2/log/log_register.c: Likewise. * db2/log/log_auto.c: Likewise. * db2/log/log_findckp.c: Likewise. * db2/mp/mp_bh.c: Likewise. * db2/mp/mp_fget.c: Likewise. * db2/mp/mp_fopen.c: Likewise. * db2/mp/mp_fput.c: Likewise. * db2/mp/mp_fset.c: Likewise. * db2/mp/mp_open.c: Likewise. * db2/mp/mp_region.c: Likewise. * db2/mp/mp_pr.c: Likewise. * db2/mp/mp_sync.c: Likewise. * db2/mutex/68020.gcc: Likewise. * db2/mutex/mutex.c: Likewise. * db2/mutex/README: Likewise. * db2/mutex/x86.gcc: Likewise. * db2/mutex/sparc.gcc: Likewise. * db2/mutex/uts4.cc.s: Likewise. * db2/mutex/alpha.dec: Likewise. * db2/mutex/alpha.gcc: Likewise. * db2/mutex/parisc.gcc: Likewise. * db2/mutex/parisc.hp: Likewise. * db2/os/db_os_abs.c: Likewise. * db2/os/db_os_dir.c: Likewise. * db2/os/db_os_fid.c: Likewise. * db2/os/db_os_lseek.c: Likewise. * db2/os/db_os_mmap.c: Likewise. * db2/os/db_os_open.c: Likewise. * db2/os/db_os_rw.c: Likewise. * db2/os/db_os_sleep.c: Likewise. * db2/os/db_os_stat.c: Likewise. * db2/os/db_os_unlink.c: Likewise. * db2/txn/txn.c: Likewise. * db2/txn/txn.src: Likewise. * db2/txn/txn_rec.c: Likewise. * db2/txn/txn_auto.c: Likewise. * db2/clib/getlong.c: Likewise. * db2/progs/db_archive/db_archive.c: Likewise. * db2/progs/db_checkpoint/db_checkpoint.c: Likewise. * db2/progs/db_deadlock/db_deadlock.c: Likewise. * db2/progs/db_dump/db_dump.c: Likewise. * db2/progs/db_dump185/db_dump185.c: Likewise. * db2/progs/db_load/db_load.c: Likewise. * db2/progs/db_printlog/db_printlog.c: Likewise. * db2/progs/db_recover/db_recover.c: Likewise. * db2/progs/db_stat/db_stat.c: Likewise. * libio/stdio.h [__cplusplus] (__STDIO_INLINE): Define as inline. * po/de.po, po/sv.po: Update from 2.0.5 translations. * sysdeps/unix/sysv/linux/netinet/tcp.h: Pretty print. * sunrpc/rpc/xdr.h (XDR): Don't define argument of x_destroy callback as const. * sunrpc/xdr_mem.c (xdrmem_destroy): Don't define argument as const. * sunrpx/xdr_rec.c (xdrrec_destroy): Likewise. * sunrpx/xdr_stdio.c (xdrstdio_destroy): Likewise. 1997-08-27 18:47 Ulrich Drepper <drepper@cygnus.com> * sysdeps/unix/sysv/linux/if_index.c: Include <errno.h>. Reported by Benjamin Kosnik <bkoz@cygnus.com>. 1997-08-27 02:27 Roland McGrath <roland@baalperazim.frob.com> * abi-tags: New file. * csu/Makefile (distribute): Remove abi-tag.h. ($(objpfx)abi-tag.h): New target. * Makefile (distribute): Add abi-tags. * sysdeps/unix/sysv/linux/abi-tag.h: File removed. * sysdeps/mach/hurd/abi-tag.h: File removed. * sysdeps/stub/abi-tag.h: File removed. 1997-08-25 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * sysdeps/unix/make-syscalls.sh: Change output so that it generates compilation rules only for the currently selected object suffixes. 1997-08-25 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * sysdeps/m68k/dl-machine.h (RTLD_START): Switch back to previous section to avoid confusing the compiler. * sysdeps/alpha/dl-machine.h (RTLD_START): Likewise. * sysdeps/i386/dl-machine.h (RTLD_START): Likewise. * sysdeps/mips/dl-machine.h (RTLD_START): Likewise. * sysdeps/mips/mips64/dl-machine.h (RTLD_START): Likewise. * sysdeps/sparc/sparc32/dl-machine.h (RTLD_START): Likewise. * sysdeps/m68k/dl-machine.h (elf_machine_load_address): Use a GOT relocation instead of a constant to avoid text relocation. (ELF_MACHINE_BEFORE_RTLD_RELOC): Removed. (RTLD_START): Declare global labels as functions and add size directive. 1997-08-25 17:01 Ulrich Drepper <drepper@cygnus.com> * sysdeps/i386/bits/select.h: Correct assembler versions to work even for descriptors >= 32. * stdlib/alloca.h: Don't define alloca to __alloca since if gcc is used __alloca is not defined to __builtin_alloca and so might not be available. Reported by Uwe Ohse <uwe@ohse.de>. * sysdeps/unix/sysv/linux/sys/sysmacros.h: Define macros in a special way if gcc is not used and so dev_t is an array. Reported by Uwe Ohse <uwe@ohse.de>. 1997-08-23 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de> * manual/libc.texinfo: Reorder chapters to match logical order. 1997-08-25 12:22 Ulrich Drepper <drepper@cygnus.com> * sunrpc/rpc/xdr.h: Change name of parameters in prototypes of xdr_reference, xdrmem_create, and xdrstdio_create because of clash with g++ internal symbols. Patch by Sudish Joseph <sj@eng.mindspring.net>. * elf/dl-deps.c: Implement handling of DT_FILTER.
106 lines
5.8 KiB
Plaintext
106 lines
5.8 KiB
Plaintext
# @(#)README 10.1 (Sleepycat) 4/12/97
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Resource locking routines: lock based on a db_mutex_t. All this gunk
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(including trying to make assembly code portable), is necessary because
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System V semaphores require system calls for uncontested locks and we
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don't want to make two system calls per resource lock.
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First, this is how it works. The db_mutex_t structure contains a resource
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test-and-set lock (tsl), a file offset, a pid for debugging and statistics
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information.
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If HAVE_SPINLOCKS is defined (i.e. we know how to do test-and-sets for
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this compiler/architecture combination), we try and lock the resource tsl
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TSL_DEFAULT_SPINS times. If we can't acquire the lock that way, we use
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a system call to sleep for 10ms, 20ms, 40ms, etc. (The time is bounded
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at 1 second, just in case.) Using the timer backoff means that there are
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two assumptions: that locks are held for brief periods (never over system
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calls or I/O) and that locks are not hotly contested.
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If HAVE_SPINLOCKS is not defined, i.e. we can't do test-and-sets, we use
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a file descriptor to do byte locking on a file at a specified offset. In
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this case, ALL of the locking is done in the kernel. Because file
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descriptors are allocated per process, we have to provide the file
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descriptor as part of the lock/unlock call. We still have to do timer
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backoff because we need to be able to block ourselves, i.e. the lock
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manager causes processes to wait by having the process acquire a mutex
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and then attempting to re-acquire the mutex. There's no way to use kernel
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locking to block yourself, i.e. if you hold a lock and attempt to
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re-acquire it, the attempt will succeed.
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Next, let's talk about why it doesn't work the way a reasonable person
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would think it should work.
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Ideally, we'd have the ability to try to lock the resource tsl, and if
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that fails, increment a counter of waiting processes, then block in the
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kernel until the tsl is released. The process holding the resource tsl
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would see the wait counter when it went to release the resource tsl, and
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would wake any waiting processes up after releasing the lock. This would
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actually require both another tsl (call it the mutex tsl) and
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synchronization between the call that blocks in the kernel and the actual
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resource tsl. The mutex tsl would be used to protect accesses to the
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db_mutex_t itself. Locking the mutex tsl would be done by a busy loop,
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which is safe because processes would never block holding that tsl (all
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they would do is try to obtain the resource tsl and set/check the wait
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count). The problem in this model is that the blocking call into the
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kernel requires a blocking semaphore, i.e. one whose normal state is
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locked.
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The only portable forms of locking under UNIX are fcntl(2) on a file
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descriptor/offset, and System V semaphores. Neither of these locking
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methods are sufficient to solve the problem.
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The problem with fcntl locking is that only the process that obtained the
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lock can release it. Remember, we want the normal state of the kernel
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semaphore to be locked. So, if the creator of the db_mutex_t were to
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initialize the lock to "locked", then a second process locks the resource
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tsl, and then a third process needs to block, waiting for the resource
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tsl, when the second process wants to wake up the third process, it can't
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because it's not the holder of the lock! For the second process to be
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the holder of the lock, we would have to make a system call per
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uncontested lock, which is what we were trying to get away from in the
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first place.
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There are some hybrid schemes, such as signaling the holder of the lock,
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or using a different blocking offset depending on which process is
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holding the lock, but it gets complicated fairly quickly. I'm open to
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suggestions, but I'm not holding my breath.
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Regardless, we use this form of locking when HAVE_SPINLOCKS is not
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defined, (i.e. we're locking in the kernel) because it doesn't have the
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limitations found in System V semaphores, and because the normal state of
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the kernel object in that case is unlocked, so the process releasing the
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lock is also the holder of the lock.
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The System V semaphore design has a number of other limitations that make
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it inappropriate for this task. Namely:
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First, the semaphore key name space is separate from the file system name
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space (although there exist methods for using file names to create
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semaphore keys). If we use a well-known key, there's no reason to believe
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that any particular key will not already be in use, either by another
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instance of the DB application or some other application, in which case
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the DB application will fail. If we create a key, then we have to use a
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file system name to rendezvous and pass around the key.
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Second, System V semaphores traditionally have compile-time, system-wide
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limits on the number of semaphore keys that you can have. Typically, that
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number is far too low for any practical purpose. Since the semaphores
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permit more than a single slot per semaphore key, we could try and get
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around that limit by using multiple slots, but that means that the file
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that we're using for rendezvous is going to have to contain slot
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information as well as semaphore key information, and we're going to be
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reading/writing it on every db_mutex_t init or destroy operation. Anyhow,
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similar compile-time, system-wide limits on the numbers of slots per
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semaphore key kick in, and you're right back where you started.
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My fantasy is that once POSIX.1 standard mutexes are in wide-spread use,
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we can switch to them. My guess is that it won't happen, because the
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POSIX semaphores are only required to work for threads within a process,
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and not independent processes.
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Note: there are races in the statistics code, but since it's just that,
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I didn't bother fixing them. (The fix requires a mutex tsl, so, when/if
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this code is fixed to do rational locking (see above), then change the
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statistics update code to acquire/release the mutex tsl.
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