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postgresql/src/include/storage/spin.h

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More cleanups of the include files - centralizing to simplify the -I's required to compile
1996-08-28 03:59:28 +02:00
/*-------------------------------------------------------------------------
*
Change my-function-name-- to my_function_name, and optimizer renames.
1999-02-14 00:22:53 +01:00
* spin.h
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
* Hardware-independent implementation of spinlocks.
*
*
* The hardware-independent interface to spinlocks is defined by the
* typedef "slock_t" and these macros:
*
Add a comment describing the requirement that pointers into shared memory that is protected by a spinlock must be volatile, per recent discussion.
2005-10-13 08:17:34 +02:00
* void SpinLockInit(volatile slock_t *lock)
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
* Initialize a spinlock (to the unlocked state).
*
Add a comment describing the requirement that pointers into shared memory that is protected by a spinlock must be volatile, per recent discussion.
2005-10-13 08:17:34 +02:00
* void SpinLockAcquire(volatile slock_t *lock)
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
* Acquire a spinlock, waiting if necessary.
* Time out and abort() if unable to acquire the lock in a
* "reasonable" amount of time --- typically ~ 1 minute.
*
Add a comment describing the requirement that pointers into shared memory that is protected by a spinlock must be volatile, per recent discussion.
2005-10-13 08:17:34 +02:00
* void SpinLockRelease(volatile slock_t *lock)
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
* Unlock a previously acquired lock.
*
* bool SpinLockFree(slock_t *lock)
Change TRUE/FALSE to true/false The lower case spellings are C and C++ standard and are used in most parts of the PostgreSQL sources. The upper case spellings are only used in some files/modules. So standardize on the standard spellings. The APIs for ICU, Perl, and Windows define their own TRUE and FALSE, so those are left as is when using those APIs. In code comments, we use the lower-case spelling for the C concepts and keep the upper-case spelling for the SQL concepts. Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
2017-08-16 06:22:32 +02:00
* Tests if the lock is free. Returns true if free, false if locked.
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
* This does *not* change the state of the lock.
*
* Callers must beware that the macro argument may be evaluated multiple
* times!
*
Remove cautions about using volatile from spin.h. Commit 0709b7ee72e4bc71ad07b7120acd117265ab51d0 obsoleted this comment but neglected to update it. Thomas Munro
2015-10-16 20:06:22 +02:00
* Load and store operations in calling code are guaranteed not to be
* reordered with respect to these operations, because they include a
* compiler barrier. (Before PostgreSQL 9.5, callers needed to use a
* volatile qualifier to access data protected by spinlocks.)
Add a comment describing the requirement that pointers into shared memory that is protected by a spinlock must be volatile, per recent discussion.
2005-10-13 08:17:34 +02:00
*
Get rid of the SpinLockAcquire/SpinLockAcquire_NoHoldoff distinction in favor of having just one set of macros that don't do HOLD/RESUME_INTERRUPTS (hence, these correspond to the old SpinLockAcquire_NoHoldoff case). Given our coding rules for spinlock use, there is no reason to allow CHECK_FOR_INTERRUPTS to be done while holding a spinlock, and also there is no situation where ImmediateInterruptOK will be true while holding a spinlock. Therefore doing HOLD/RESUME_INTERRUPTS while taking/releasing a spinlock is just a waste of cycles. Qingqing Zhou and Tom Lane.
2005-12-29 19:08:05 +01:00
* Keep in mind the coding rule that spinlocks must not be held for more
* than a few instructions. In particular, we assume it is not possible
* for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
* it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
*
Add a comment describing the requirement that pointers into shared memory that is protected by a spinlock must be volatile, per recent discussion.
2005-10-13 08:17:34 +02:00
* These macros are implemented in terms of hardware-dependent macros
Get rid of the SpinLockAcquire/SpinLockAcquire_NoHoldoff distinction in favor of having just one set of macros that don't do HOLD/RESUME_INTERRUPTS (hence, these correspond to the old SpinLockAcquire_NoHoldoff case). Given our coding rules for spinlock use, there is no reason to allow CHECK_FOR_INTERRUPTS to be done while holding a spinlock, and also there is no situation where ImmediateInterruptOK will be true while holding a spinlock. Therefore doing HOLD/RESUME_INTERRUPTS while taking/releasing a spinlock is just a waste of cycles. Qingqing Zhou and Tom Lane.
2005-12-29 19:08:05 +01:00
* supplied by s_lock.h. There is not currently any extra functionality
* added by this header, but there has been in the past and may someday
* be again.
More cleanups of the include files - centralizing to simplify the -I's required to compile
1996-08-28 03:59:28 +02:00
*
*
Update copyright for 2023 Backpatch-through: 11
2023-01-02 21:00:37 +01:00
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
Add: * Portions Copyright (c) 1996-2000, PostgreSQL, Inc to all files copyright Regents of Berkeley. Man, that's a lot of files.
2000-01-26 06:58:53 +01:00
* Portions Copyright (c) 1994, Regents of the University of California
More cleanups of the include files - centralizing to simplify the -I's required to compile
1996-08-28 03:59:28 +02:00
*
Remove cvs keywords from all files.
2010-09-20 22:08:53 +02:00
* src/include/storage/spin.h
More cleanups of the include files - centralizing to simplify the -I's required to compile
1996-08-28 03:59:28 +02:00
*
*-------------------------------------------------------------------------
*/
#ifndef SPIN_H
#define SPIN_H
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
#include "storage/s_lock.h"
We don't need to include pg_sema.h in s_lock.h anymore. Minor improvement to commit daa7527afc2274432094ebe7ceb03aa41f916607: s_lock.h no longer has any need to mention PGSemaphoreData, so we can rip out the #include that supplies that. In a non-HAVE_SPINLOCKS build, this doesn't really buy much since we still need the #include in spin.h --- but everywhere else, this reduces #include footprint by some trifle, and helps keep the different locking facilities separate.
2014-01-09 02:58:22 +01:00
#ifndef HAVE_SPINLOCKS
#include "storage/pg_sema.h"
#endif
More cleanups of the include files - centralizing to simplify the -I's required to compile
1996-08-28 03:59:28 +02:00
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
#define SpinLockInit(lock) S_INIT_LOCK(lock)
Get rid of the SpinLockAcquire/SpinLockAcquire_NoHoldoff distinction in favor of having just one set of macros that don't do HOLD/RESUME_INTERRUPTS (hence, these correspond to the old SpinLockAcquire_NoHoldoff case). Given our coding rules for spinlock use, there is no reason to allow CHECK_FOR_INTERRUPTS to be done while holding a spinlock, and also there is no situation where ImmediateInterruptOK will be true while holding a spinlock. Therefore doing HOLD/RESUME_INTERRUPTS while taking/releasing a spinlock is just a waste of cycles. Qingqing Zhou and Tom Lane.
2005-12-29 19:08:05 +01:00
#define SpinLockAcquire(lock) S_LOCK(lock)
pgindent run. Make it all clean.
2001-03-22 05:01:46 +01:00
Get rid of the SpinLockAcquire/SpinLockAcquire_NoHoldoff distinction in favor of having just one set of macros that don't do HOLD/RESUME_INTERRUPTS (hence, these correspond to the old SpinLockAcquire_NoHoldoff case). Given our coding rules for spinlock use, there is no reason to allow CHECK_FOR_INTERRUPTS to be done while holding a spinlock, and also there is no situation where ImmediateInterruptOK will be true while holding a spinlock. Therefore doing HOLD/RESUME_INTERRUPTS while taking/releasing a spinlock is just a waste of cycles. Qingqing Zhou and Tom Lane.
2005-12-29 19:08:05 +01:00
#define SpinLockRelease(lock) S_UNLOCK(lock)
The heralded `Grand Unified Configuration scheme' (GUC) That means you can now set your options in either or all of $PGDATA/configuration, some postmaster option (--enable-fsync=off), or set a SET command. The list of options is in backend/utils/misc/guc.c, documentation will be written post haste. pg_options is gone, so is that pq_geqo config file. Also removed were backend -K, -Q, and -T options (no longer applicable, although -d0 does the same as -Q). Added to configure an --enable-syslog option. changed all callers from TPRINTF to elog(DEBUG)
2000-05-31 02:28:42 +02:00
Implement new 'lightweight lock manager' that's intermediate between existing lock manager and spinlocks: it understands exclusive vs shared lock but has few other fancy features. Replace most uses of spinlocks with lightweight locks. All remaining uses of spinlocks have very short lock hold times (a few dozen instructions), so tweak spinlock backoff code to work efficiently given this assumption. All per my proposal on pghackers 26-Sep-01.
2001-09-29 06:02:27 +02:00
#define SpinLockFree(lock) S_LOCK_FREE(lock)
Significant cleanups in SysV IPC handling (shared mem and semaphores). IPC key assignment will now work correctly even when multiple postmasters are using same logical port number (which is possible given -k switch). There is only one shared-mem segment per postmaster now, not 3. Rip out broken code for non-TAS case in bufmgr and xlog, substitute a complete S_LOCK emulation using semaphores in spin.c. TAS and non-TAS logic is now exactly the same. When deadlock is detected, "Deadlock detected" is now the elog(ERROR) message, rather than a NOTICE that comes out before an unhelpful ERROR.
2000-11-29 00:27:57 +01:00
Create an internal semaphore API that is not tied to SysV semaphores. As proof of concept, provide an alternate implementation based on POSIX semaphores. Also push the SysV shared-memory implementation into a separate file so that it can be replaced conveniently.
2002-05-05 02:03:29 +02:00
extern int SpinlockSemas(void);
Reduce the number of semaphores used under --disable-spinlocks. Instead of allocating a semaphore from the operating system for every spinlock, allocate a fixed number of semaphores (by default, 1024) from the operating system and multiplex all the spinlocks that get created onto them. This could self-deadlock if a process attempted to acquire more than one spinlock at a time, but since processes aren't supposed to execute anything other than short stretches of straight-line code while holding a spinlock, that shouldn't happen. One motivation for this change is that, with the introduction of dynamic shared memory, it may be desirable to create spinlocks that last for less than the lifetime of the server. Without this change, attempting to use such facilities under --disable-spinlocks would quickly exhaust any supply of available semaphores. Quite apart from that, it's desirable to contain the quantity of semaphores needed to run the server simply on convenience grounds, since using too many may make it harder to get PostgreSQL running on a new platform, which is mostly the point of --disable-spinlocks in the first place. Patch by me; review by Tom Lane.
2014-01-09 00:49:14 +01:00
extern Size SpinlockSemaSize(void);
#ifndef HAVE_SPINLOCKS
Make the different Unix-y semaphore implementations ABI-compatible. Previously, the "sem" field of PGPROC varied in size depending on which kernel semaphore API we were using. That was okay as long as there was only one likely choice per platform, but in the wake of commit ecb0d20a9, that assumption seems rather shaky. It doesn't seem out of the question anymore that an extension compiled against one API choice might be loaded into a postmaster built with another choice. Moreover, this prevents any possibility of selecting the semaphore API at postmaster startup, which might be something we want to do in future. Hence, change PGPROC.sem to be PGSemaphore (i.e. a pointer) for all Unix semaphore APIs, and turn the pointed-to data into an opaque struct whose contents are only known within the responsible modules. For the SysV and unnamed-POSIX APIs, the pointed-to data has to be allocated elsewhere in shared memory, which takes a little bit of rejiggering of the InitShmemAllocation code sequence. (I invented a ShmemAllocUnlocked() function to make that a little cleaner than it used to be. That function is not meant for any uses other than the ones it has now, but it beats having InitShmemAllocation() know explicitly about allocation of space for semaphores and spinlocks.) This change means an extra indirection to access the semaphore data, but since we only touch that when blocking or awakening a process, there shouldn't be any meaningful performance penalty. Moreover, at least for the unnamed-POSIX case on Linux, the sem_t type is quite a bit wider than a pointer, so this reduces sizeof(PGPROC) which seems like a good thing. For the named-POSIX API, there's effectively no change: the PGPROC.sem field was and still is a pointer to something returned by sem_open() in the postmaster's memory space. Document and check the pre-existing limitation that this case can't work in EXEC_BACKEND mode. It did not seem worth unifying the Windows semaphore ABI with the Unix cases, since there's no likelihood of needing ABI compatibility much less runtime switching across those cases. However, we can simplify the Windows code a bit if we define PGSemaphore as being directly a HANDLE, rather than pointer to HANDLE, so let's do that while we're here. (This also ends up being no change in what's physically stored in PGPROC.sem. We're just moving the HANDLE fetch from callees to callers.) It would take a bunch of additional code shuffling to get to the point of actually choosing a semaphore API at postmaster start, but the effects of that would now be localized in the port/XXX_sema.c files, so it seems like fit material for a separate patch. The need for it is unproven as yet, anyhow, whereas the ABI risk to extensions seems real enough. Discussion: https://postgr.es/m/4029.1481413370@sss.pgh.pa.us
2016-12-12 19:32:10 +01:00
extern void SpinlockSemaInit(void);
Apply PGDLLIMPORT markings broadly. Up until now, we've had a policy of only marking certain variables in the PostgreSQL header files with PGDLLIMPORT, but now we've decided to mark them all. This means that extensions running on Windows should no longer operate at a disadvantage as compared to extensions running on Linux: if the variable is present in a header file, it should be accessible. Discussion: http://postgr.es/m/CA+TgmoYanc1_FSfimhgiWSqVyP5KKmh5NP2BWNwDhO8Pg2vGYQ@mail.gmail.com
2022-04-08 14:16:38 +02:00
extern PGDLLIMPORT PGSemaphore *SpinlockSemaArray;
Reduce the number of semaphores used under --disable-spinlocks. Instead of allocating a semaphore from the operating system for every spinlock, allocate a fixed number of semaphores (by default, 1024) from the operating system and multiplex all the spinlocks that get created onto them. This could self-deadlock if a process attempted to acquire more than one spinlock at a time, but since processes aren't supposed to execute anything other than short stretches of straight-line code while holding a spinlock, that shouldn't happen. One motivation for this change is that, with the introduction of dynamic shared memory, it may be desirable to create spinlocks that last for less than the lifetime of the server. Without this change, attempting to use such facilities under --disable-spinlocks would quickly exhaust any supply of available semaphores. Quite apart from that, it's desirable to contain the quantity of semaphores needed to run the server simply on convenience grounds, since using too many may make it harder to get PostgreSQL running on a new platform, which is mostly the point of --disable-spinlocks in the first place. Patch by me; review by Tom Lane.
2014-01-09 00:49:14 +01:00
#endif
Another pgindent run. Fixes enum indenting, and improves #endif spacing. Also adds space for one-line comments.
2001-10-28 07:26:15 +01:00
More cleanups of the include files - centralizing to simplify the -I's required to compile
1996-08-28 03:59:28 +02:00
#endif /* SPIN_H */