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Use condition variables for ProcSignalBarriers.

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Instead of a poll/sleep loop, use a condition variable for precise
wake-up whenever a backend's pss_barrierGeneration advances.

Discussion: https://postgr.es/m/CA+hUKGLdemy2gBm80kz20GTe6hNVwoErE8KwcJk6-U56oStjtg@mail.gmail.com
This commit is contained in:
Thomas Munro
2021-03-01 16:26:22 +13:00
parent 8bdb1332eb
commit 814f1d8bc3
1 changed files with 14 additions and 20 deletions
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34
src/backend/storage/ipc/procsignal.c
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@ -23,6 +23,7 @@
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/walsender.h"
#include "storage/condition_variable.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/proc.h"
@ -59,10 +60,11 @@
*/
typedef struct
{
pid_t pss_pid;
sig_atomic_t pss_signalFlags[NUM_PROCSIGNALS];
volatile pid_t pss_pid;
volatile sig_atomic_t pss_signalFlags[NUM_PROCSIGNALS];
pg_atomic_uint64 pss_barrierGeneration;
pg_atomic_uint32 pss_barrierCheckMask;
ConditionVariable pss_barrierCV;
} ProcSignalSlot;
/*
@ -93,7 +95,7 @@ typedef struct
((flags) &= ~(((uint32) 1) << (uint32) (type)))
static ProcSignalHeader *ProcSignal = NULL;
static volatile ProcSignalSlot *MyProcSignalSlot = NULL;
static ProcSignalSlot *MyProcSignalSlot = NULL;
static bool CheckProcSignal(ProcSignalReason reason);
static void CleanupProcSignalState(int status, Datum arg);
@ -142,6 +144,7 @@ ProcSignalShmemInit(void)
MemSet(slot->pss_signalFlags, 0, sizeof(slot->pss_signalFlags));
pg_atomic_init_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
pg_atomic_init_u32(&slot->pss_barrierCheckMask, 0);
ConditionVariableInit(&slot->pss_barrierCV);
}
}
}
@ -156,7 +159,7 @@ ProcSignalShmemInit(void)
void
ProcSignalInit(int pss_idx)
{
volatile ProcSignalSlot *slot;
ProcSignalSlot *slot;
uint64 barrier_generation;
Assert(pss_idx >= 1 && pss_idx <= NumProcSignalSlots);
@ -208,7 +211,7 @@ static void
CleanupProcSignalState(int status, Datum arg)
{
int pss_idx = DatumGetInt32(arg);
volatile ProcSignalSlot *slot;
ProcSignalSlot *slot;
slot = &ProcSignal->psh_slot[pss_idx - 1];
Assert(slot == MyProcSignalSlot);
@ -237,6 +240,7 @@ CleanupProcSignalState(int status, Datum arg)
* no barrier waits block on it.
*/
pg_atomic_write_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
ConditionVariableBroadcast(&slot->pss_barrierCV);
slot->pss_pid = 0;
}
@ -391,13 +395,11 @@ EmitProcSignalBarrier(ProcSignalBarrierType type)
void
WaitForProcSignalBarrier(uint64 generation)
{
long timeout = 125L;
Assert(generation <= pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration));
for (int i = NumProcSignalSlots - 1; i >= 0; i--)
{
volatile ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
uint64 oldval;
/*
@ -409,20 +411,11 @@ WaitForProcSignalBarrier(uint64 generation)
oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
while (oldval < generation)
{
int events;
CHECK_FOR_INTERRUPTS();
events =
WaitLatch(MyLatch,
WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
timeout, WAIT_EVENT_PROC_SIGNAL_BARRIER);
ResetLatch(MyLatch);
ConditionVariableSleep(&slot->pss_barrierCV,
WAIT_EVENT_PROC_SIGNAL_BARRIER);
oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
if (events & WL_TIMEOUT)
timeout = Min(timeout * 2, 1000L);
}
ConditionVariableCancelSleep();
}
/*
@ -589,6 +582,7 @@ ProcessProcSignalBarrier(void)
* next called.
*/
pg_atomic_write_u64(&MyProcSignalSlot->pss_barrierGeneration, shared_gen);
ConditionVariableBroadcast(&MyProcSignalSlot->pss_barrierCV);
}
/*