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Add a default local latch for use in signal handlers.

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To do so, move InitializeLatchSupport() into the new common process
initialization functions, and add a new global variable MyLatch.

MyLatch is usable as soon InitPostmasterChild() has been called
(i.e. very early during startup). Initially it points to a process
local latch that exists in all processes. InitProcess/InitAuxiliaryProcess
then replaces that local latch with PGPROC->procLatch. During shutdown
the reverse happens.

This is primarily advantageous for two reasons: For one it simplifies
dealing with the shared process latch, especially in signal handlers,
because instead of having to check for MyProc, MyLatch can be used
unconditionally. For another, a later patch that makes FEs/BE
communication use latches, now can rely on the existence of a latch,
even before having gone through InitProcess.

Discussion: 20140927191243.GD5423@alap3.anarazel.de
This commit is contained in:
Andres Freund
2015-01-14 18:45:22 +01:00
parent 85a2a8903f
commit 59f71a0d0b
23 changed files with 136 additions and 134 deletions
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9
src/backend/utils/init/globals.c
View File

@@ -40,6 +40,15 @@ struct Port *MyProcPort;
long MyCancelKey;
int MyPMChildSlot;
/*
* MyLatch points to the latch that should be used for signal handling by the
* current process. It will either point to a process local latch if the
* current process does not have a PGPROC entry in that moment, or to
* PGPROC->procLatch if it has. Thus it can always be used in signal handlers,
* without checking for its existence.
*/
struct Latch *MyLatch;
/*
* DataDir is the absolute path to the top level of the PGDATA directory tree.
* Except during early startup, this is also the server's working directory;

37
src/backend/utils/init/miscinit.c
View File

@@ -39,6 +39,7 @@
#include "postmaster/postmaster.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/procarray.h"
@@ -55,6 +56,7 @@ ProcessingMode Mode = InitProcessing;
/* List of lock files to be removed at proc exit */
static List *lock_files = NIL;
static Latch LocalLatchData;
/* ----------------------------------------------------------------
* ignoring system indexes support stuff
@@ -189,6 +191,11 @@ InitPostmasterChild(void)
/* We don't want the postmaster's proc_exit() handlers */
on_exit_reset();
/* Initialize process-local latch support */
InitializeLatchSupport();
MyLatch = &LocalLatchData;
InitLatch(MyLatch);
/*
* If possible, make this process a group leader, so that the postmaster
* can signal any child processes too. Not all processes will have
@@ -215,6 +222,11 @@ InitStandaloneProcess(const char *argv0)
MyStartTime = time(NULL); /* set our start time in case we call elog */
/* Initialize process-local latch support */
InitializeLatchSupport();
MyLatch = &LocalLatchData;
InitLatch(MyLatch);
/* Compute paths, no postmaster to inherit from */
if (my_exec_path[0] == '\0')
{
@@ -227,6 +239,31 @@ InitStandaloneProcess(const char *argv0)
get_pkglib_path(my_exec_path, pkglib_path);
}
void
SwitchToSharedLatch(void)
{
Assert(MyLatch == &LocalLatchData);
Assert(MyProc != NULL);
MyLatch = &MyProc->procLatch;
/*
* Set the shared latch as the local one might have been set. This
* shouldn't normally be necessary as code is supposed to check the
* condition before waiting for the latch, but a bit care can't hurt.
*/
SetLatch(MyLatch);
}
void
SwitchBackToLocalLatch(void)
{
Assert(MyLatch != &LocalLatchData);
Assert(MyProc != NULL && MyLatch == &MyProc->procLatch);
MyLatch = &LocalLatchData;
SetLatch(MyLatch);
}
/*
* GetUserId - get the current effective user ID.
*