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Commit236b6bc

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Simplify Windows implementation of latches. There's no need to keep a
dynamic pool of event handles, we can permanently assign one for eachshared latch. Thanks to that, we no longer need a separate shared memoryblock for latches, and we don't need to know in advance how many sharedlatches there is, so you no longer need to remember to updateNumSharedLatches when you introduce a new latch to the system.
1 parent1eab7a5 commit236b6bc

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4 files changed

+39
-153
lines changed

4 files changed

+39
-153
lines changed

‎src/backend/port/unix_latch.c‎

Lines changed: 5 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -77,7 +77,7 @@
7777
* Portions Copyright (c) 1994, Regents of the University of California
7878
*
7979
* IDENTIFICATION
80-
* $PostgreSQL: pgsql/src/backend/port/unix_latch.c,v 1.3 2010/09/13 18:01:20 heikki Exp $
80+
* $PostgreSQL: pgsql/src/backend/port/unix_latch.c,v 1.4 2010/09/15 10:06:21 heikki Exp $
8181
*
8282
*-------------------------------------------------------------------------
8383
*/
@@ -129,8 +129,10 @@ InitLatch(volatile Latch *latch)
129129
* is initially owned by no-one, use OwnLatch to associate it with the
130130
* current process.
131131
*
132-
* NB: When you introduce a new shared latch, you must increase the shared
133-
* latch count in NumSharedLatches in win32_latch.c!
132+
* InitSharedLatch needs to be called in postmaster before forking child
133+
* processes, usually right after allocating the shared memory block
134+
* containing the latch with ShmemInitStruct. The Unix implementation
135+
* doesn't actually require that, but the Windows one does.
134136
*/
135137
void
136138
InitSharedLatch(volatileLatch*latch)
@@ -322,29 +324,6 @@ ResetLatch(volatile Latch *latch)
322324
latch->is_set= false;
323325
}
324326

325-
/*
326-
* LatchShmemSize
327-
*Compute space needed for latch's shared memory
328-
*
329-
* Not needed for Unix implementation.
330-
*/
331-
Size
332-
LatchShmemSize(void)
333-
{
334-
return0;
335-
}
336-
337-
/*
338-
* LatchShmemInit
339-
*Allocate and initialize shared memory needed for latches
340-
*
341-
* Not needed for Unix implementation.
342-
*/
343-
void
344-
LatchShmemInit(void)
345-
{
346-
}
347-
348327
/*
349328
* SetLatch uses SIGUSR1 to wake up the process waiting on the latch. Wake
350329
* up WaitLatch.

‎src/backend/port/win32_latch.c‎

Lines changed: 31 additions & 117 deletions
Original file line numberDiff line numberDiff line change
@@ -3,14 +3,16 @@
33
* win32_latch.c
44
* Windows implementation of latches.
55
*
6-
* The Windows implementation uses Windows events. See unix_latch.c for
7-
* information on usage.
6+
* See unix_latch.c for information on usage.
7+
*
8+
* The Windows implementation uses Windows events that are inherited by
9+
* all postmaster child processes.
810
*
911
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
1012
* Portions Copyright (c) 1994, Regents of the University of California
1113
*
1214
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/backend/port/win32_latch.c,v 1.1 2010/09/11 15:48:04 heikki Exp $
15+
* $PostgreSQL: pgsql/src/backend/port/win32_latch.c,v 1.2 2010/09/15 10:06:21 heikki Exp $
1416
*
1517
*-------------------------------------------------------------------------
1618
*/
@@ -24,83 +26,60 @@
2426
#include"replication/walsender.h"
2527
#include"storage/latch.h"
2628
#include"storage/shmem.h"
27-
#include"storage/spin.h"
28-
29-
/*
30-
* Shared latches are implemented with Windows events that are shared by
31-
* all postmaster child processes. At postmaster startup we create enough
32-
* Event objects, and mark them as inheritable so that they are accessible
33-
* in child processes. The handles are stored in sharedHandles.
34-
*/
35-
typedefstruct
36-
{
37-
slock_tmutex;/* protects all the other fields */
3829

39-
intmaxhandles;/* number of shared handles created */
40-
intnfreehandles;/* number of free handles in array */
41-
HANDLEhandles[1];/* free handles, variable length */
42-
}SharedEventHandles;
43-
44-
staticSharedEventHandles*sharedHandles;
4530

4631
void
4732
InitLatch(volatileLatch*latch)
4833
{
49-
latch->event=CreateEvent(NULL, TRUE, FALSE,NULL);
50-
latch->is_shared= false;
5134
latch->is_set= false;
35+
latch->owner_pid=MyProcPid;
36+
latch->is_shared= false;
37+
38+
latch->event=CreateEvent(NULL, TRUE, FALSE,NULL);
39+
if (latch->event==NULL)
40+
elog(ERROR,"CreateEvent failed: error code %d", (int)GetLastError());
5241
}
5342

5443
void
5544
InitSharedLatch(volatileLatch*latch)
5645
{
57-
latch->is_shared= true;
46+
SECURITY_ATTRIBUTESsa;
47+
5848
latch->is_set= false;
59-
latch->event=NULL;
49+
latch->owner_pid=0;
50+
latch->is_shared= true;
51+
52+
/*
53+
* Set up security attributes to specify that the events are
54+
* inherited.
55+
*/
56+
ZeroMemory(&sa,sizeof(sa));
57+
sa.nLength=sizeof(sa);
58+
sa.bInheritHandle= TRUE;
59+
60+
latch->event=CreateEvent(&sa, TRUE, FALSE,NULL);
61+
if (latch->event==NULL)
62+
elog(ERROR,"CreateEvent failed: error code %d", (int)GetLastError());
6063
}
6164

6265
void
6366
OwnLatch(volatileLatch*latch)
6467
{
65-
HANDLEevent;
66-
6768
/* Sanity checks */
6869
Assert(latch->is_shared);
69-
if (latch->event!=0)
70+
if (latch->owner_pid!=0)
7071
elog(ERROR,"latch already owned");
7172

72-
/* Reserve an event handle from the shared handles array */
73-
SpinLockAcquire(&sharedHandles->mutex);
74-
if (sharedHandles->nfreehandles <=0)
75-
{
76-
SpinLockRelease(&sharedHandles->mutex);
77-
elog(ERROR,"out of shared event objects");
78-
}
79-
sharedHandles->nfreehandles--;
80-
event=sharedHandles->handles[sharedHandles->nfreehandles];
81-
SpinLockRelease(&sharedHandles->mutex);
82-
83-
latch->event=event;
73+
latch->owner_pid=MyProcPid;
8474
}
8575

8676
void
8777
DisownLatch(volatileLatch*latch)
8878
{
8979
Assert(latch->is_shared);
90-
Assert(latch->event!=NULL);
91-
92-
/* Put the event handle back to the pool */
93-
SpinLockAcquire(&sharedHandles->mutex);
94-
if (sharedHandles->nfreehandles >=sharedHandles->maxhandles)
95-
{
96-
SpinLockRelease(&sharedHandles->mutex);
97-
elog(PANIC,"too many free event handles");
98-
}
99-
sharedHandles->handles[sharedHandles->nfreehandles]=latch->event;
100-
sharedHandles->nfreehandles++;
101-
SpinLockRelease(&sharedHandles->mutex);
80+
Assert(latch->owner_pid==MyProcPid);
10281

103-
latch->event=NULL;
82+
latch->owner_pid=0;
10483
}
10584

10685
bool
@@ -217,68 +196,3 @@ ResetLatch(volatile Latch *latch)
217196
{
218197
latch->is_set= false;
219198
}
220-
221-
/*
222-
* Number of shared latches, used to allocate the right number of shared
223-
* Event handles at postmaster startup. You must update this if you
224-
* introduce a new shared latch!
225-
*/
226-
staticint
227-
NumSharedLatches(void)
228-
{
229-
intnumLatches=0;
230-
231-
/* Each walsender needs one latch */
232-
numLatches+=max_wal_senders;
233-
234-
returnnumLatches;
235-
}
236-
237-
/*
238-
* LatchShmemSize
239-
*Compute space needed for latch's shared memory
240-
*/
241-
Size
242-
LatchShmemSize(void)
243-
{
244-
return offsetof(SharedEventHandles,handles)+
245-
NumSharedLatches()*sizeof(HANDLE);
246-
}
247-
248-
/*
249-
* LatchShmemInit
250-
*Allocate and initialize shared memory needed for latches
251-
*/
252-
void
253-
LatchShmemInit(void)
254-
{
255-
Sizesize=LatchShmemSize();
256-
boolfound;
257-
258-
sharedHandles=ShmemInitStruct("SharedEventHandles",size,&found);
259-
260-
/* If we're first, initialize the struct and allocate handles */
261-
if (!found)
262-
{
263-
inti;
264-
SECURITY_ATTRIBUTESsa;
265-
266-
/*
267-
* Set up security attributes to specify that the events are
268-
* inherited.
269-
*/
270-
ZeroMemory(&sa,sizeof(sa));
271-
sa.nLength=sizeof(sa);
272-
sa.bInheritHandle= TRUE;
273-
274-
SpinLockInit(&sharedHandles->mutex);
275-
sharedHandles->maxhandles=NumSharedLatches();
276-
sharedHandles->nfreehandles=sharedHandles->maxhandles;
277-
for (i=0;i<sharedHandles->maxhandles;i++)
278-
{
279-
sharedHandles->handles[i]=CreateEvent(&sa, TRUE, FALSE,NULL);
280-
if (sharedHandles->handles[i]==NULL)
281-
elog(ERROR,"CreateEvent failed: error code %d", (int)GetLastError());
282-
}
283-
}
284-
}

‎src/backend/storage/ipc/ipci.c‎

Lines changed: 1 addition & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.105 2010/09/11 15:48:04 heikki Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.106 2010/09/15 10:06:21 heikki Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -30,7 +30,6 @@
3030
#include"replication/walsender.h"
3131
#include"storage/bufmgr.h"
3232
#include"storage/ipc.h"
33-
#include"storage/latch.h"
3433
#include"storage/pg_shmem.h"
3534
#include"storage/pmsignal.h"
3635
#include"storage/procarray.h"
@@ -118,7 +117,6 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
118117
size=add_size(size,SInvalShmemSize());
119118
size=add_size(size,PMSignalShmemSize());
120119
size=add_size(size,ProcSignalShmemSize());
121-
size=add_size(size,LatchShmemSize());
122120
size=add_size(size,BgWriterShmemSize());
123121
size=add_size(size,AutoVacuumShmemSize());
124122
size=add_size(size,WalSndShmemSize());
@@ -219,7 +217,6 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
219217
*/
220218
PMSignalShmemInit();
221219
ProcSignalShmemInit();
222-
LatchShmemInit();
223220
BgWriterShmemInit();
224221
AutoVacuumShmemInit();
225222
WalSndShmemInit();

‎src/include/storage/latch.h‎

Lines changed: 2 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/storage/latch.h,v 1.1 2010/09/11 15:48:04 heikki Exp $
10+
* $PostgreSQL: pgsql/src/include/storage/latch.h,v 1.2 2010/09/15 10:06:21 heikki Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -25,9 +25,8 @@ typedef struct
2525
{
2626
sig_atomic_tis_set;
2727
boolis_shared;
28-
#ifndefWIN32
2928
intowner_pid;
30-
#else
29+
#ifdefWIN32
3130
HANDLEevent;
3231
#endif
3332
}Latch;
@@ -46,9 +45,6 @@ extern void SetLatch(volatile Latch *latch);
4645
externvoidResetLatch(volatileLatch*latch);
4746
#defineTestLatch(latch) (((volatile Latch *) latch)->is_set)
4847

49-
externSizeLatchShmemSize(void);
50-
externvoidLatchShmemInit(void);
51-
5248
/*
5349
* Unix implementation uses SIGUSR1 for inter-process signaling, Win32 doesn't
5450
* need this.

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