396 lines
11 KiB
C
396 lines
11 KiB
C
/*-------------------------------------------------------------------------
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*
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* pmsignal.c
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* routines for signaling the postmaster from its child processes
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*
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* src/backend/storage/ipc/pmsignal.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <signal.h>
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#include <unistd.h>
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#ifdef HAVE_SYS_PRCTL_H
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#include <sys/prctl.h>
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#endif
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#include "miscadmin.h"
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#include "postmaster/postmaster.h"
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#include "replication/walsender.h"
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#include "storage/pmsignal.h"
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#include "storage/shmem.h"
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/*
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* The postmaster is signaled by its children by sending SIGUSR1. The
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* specific reason is communicated via flags in shared memory. We keep
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* a boolean flag for each possible "reason", so that different reasons
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* can be signaled by different backends at the same time. (However,
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* if the same reason is signaled more than once simultaneously, the
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* postmaster will observe it only once.)
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*
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* The flags are actually declared as "volatile sig_atomic_t" for maximum
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* portability. This should ensure that loads and stores of the flag
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* values are atomic, allowing us to dispense with any explicit locking.
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*
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* In addition to the per-reason flags, we store a set of per-child-process
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* flags that are currently used only for detecting whether a backend has
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* exited without performing proper shutdown. The per-child-process flags
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* have three possible states: UNUSED, ASSIGNED, ACTIVE. An UNUSED slot is
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* available for assignment. An ASSIGNED slot is associated with a postmaster
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* child process, but either the process has not touched shared memory yet,
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* or it has successfully cleaned up after itself. A ACTIVE slot means the
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* process is actively using shared memory. The slots are assigned to
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* child processes at random, and postmaster.c is responsible for tracking
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* which one goes with which PID.
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*
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* Actually there is a fourth state, WALSENDER. This is just like ACTIVE,
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* but carries the extra information that the child is a WAL sender.
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* WAL senders too start in ACTIVE state, but switch to WALSENDER once they
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* start streaming the WAL (and they never go back to ACTIVE after that).
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*/
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#define PM_CHILD_UNUSED 0 /* these values must fit in sig_atomic_t */
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#define PM_CHILD_ASSIGNED 1
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#define PM_CHILD_ACTIVE 2
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#define PM_CHILD_WALSENDER 3
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/* "typedef struct PMSignalData PMSignalData" appears in pmsignal.h */
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struct PMSignalData
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{
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/* per-reason flags */
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sig_atomic_t PMSignalFlags[NUM_PMSIGNALS];
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/* per-child-process flags */
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int num_child_flags; /* # of entries in PMChildFlags[] */
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int next_child_flag; /* next slot to try to assign */
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sig_atomic_t PMChildFlags[FLEXIBLE_ARRAY_MEMBER];
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};
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NON_EXEC_STATIC volatile PMSignalData *PMSignalState = NULL;
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/*
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* Signal handler to be notified if postmaster dies.
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*/
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#ifdef USE_POSTMASTER_DEATH_SIGNAL
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volatile sig_atomic_t postmaster_possibly_dead = false;
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static void
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postmaster_death_handler(int signo)
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{
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postmaster_possibly_dead = true;
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}
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/*
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* The available signals depend on the OS. SIGUSR1 and SIGUSR2 are already
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* used for other things, so choose another one.
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*
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* Currently, we assume that we can always find a signal to use. That
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* seems like a reasonable assumption for all platforms that are modern
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* enough to have a parent-death signaling mechanism.
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*/
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#if defined(SIGINFO)
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#define POSTMASTER_DEATH_SIGNAL SIGINFO
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#elif defined(SIGPWR)
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#define POSTMASTER_DEATH_SIGNAL SIGPWR
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#else
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#error "cannot find a signal to use for postmaster death"
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#endif
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#endif /* USE_POSTMASTER_DEATH_SIGNAL */
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/*
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* PMSignalShmemSize
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* Compute space needed for pmsignal.c's shared memory
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*/
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Size
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PMSignalShmemSize(void)
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{
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Size size;
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size = offsetof(PMSignalData, PMChildFlags);
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size = add_size(size, mul_size(MaxLivePostmasterChildren(),
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sizeof(sig_atomic_t)));
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return size;
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}
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/*
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* PMSignalShmemInit - initialize during shared-memory creation
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*/
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void
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PMSignalShmemInit(void)
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{
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bool found;
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PMSignalState = (PMSignalData *)
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ShmemInitStruct("PMSignalState", PMSignalShmemSize(), &found);
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if (!found)
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{
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MemSet(unvolatize(PMSignalData *, PMSignalState), 0, PMSignalShmemSize());
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PMSignalState->num_child_flags = MaxLivePostmasterChildren();
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}
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}
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/*
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* SendPostmasterSignal - signal the postmaster from a child process
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*/
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void
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SendPostmasterSignal(PMSignalReason reason)
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{
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/* If called in a standalone backend, do nothing */
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if (!IsUnderPostmaster)
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return;
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/* Atomically set the proper flag */
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PMSignalState->PMSignalFlags[reason] = true;
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/* Send signal to postmaster */
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kill(PostmasterPid, SIGUSR1);
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}
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/*
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* CheckPostmasterSignal - check to see if a particular reason has been
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* signaled, and clear the signal flag. Should be called by postmaster
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* after receiving SIGUSR1.
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*/
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bool
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CheckPostmasterSignal(PMSignalReason reason)
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{
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/* Careful here --- don't clear flag if we haven't seen it set */
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if (PMSignalState->PMSignalFlags[reason])
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{
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PMSignalState->PMSignalFlags[reason] = false;
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return true;
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}
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return false;
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}
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/*
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* AssignPostmasterChildSlot - select an unused slot for a new postmaster
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* child process, and set its state to ASSIGNED. Returns a slot number
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* (one to N).
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*
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* Only the postmaster is allowed to execute this routine, so we need no
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* special locking.
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*/
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int
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AssignPostmasterChildSlot(void)
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{
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int slot = PMSignalState->next_child_flag;
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int n;
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/*
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* Scan for a free slot. We track the last slot assigned so as not to
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* waste time repeatedly rescanning low-numbered slots.
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*/
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for (n = PMSignalState->num_child_flags; n > 0; n--)
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{
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if (--slot < 0)
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slot = PMSignalState->num_child_flags - 1;
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if (PMSignalState->PMChildFlags[slot] == PM_CHILD_UNUSED)
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{
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PMSignalState->PMChildFlags[slot] = PM_CHILD_ASSIGNED;
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PMSignalState->next_child_flag = slot;
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return slot + 1;
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}
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}
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/* Out of slots ... should never happen, else postmaster.c messed up */
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elog(FATAL, "no free slots in PMChildFlags array");
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return 0; /* keep compiler quiet */
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}
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/*
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* ReleasePostmasterChildSlot - release a slot after death of a postmaster
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* child process. This must be called in the postmaster process.
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*
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* Returns true if the slot had been in ASSIGNED state (the expected case),
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* false otherwise (implying that the child failed to clean itself up).
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*/
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bool
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ReleasePostmasterChildSlot(int slot)
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{
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bool result;
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Assert(slot > 0 && slot <= PMSignalState->num_child_flags);
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slot--;
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/*
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* Note: the slot state might already be unused, because the logic in
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* postmaster.c is such that this might get called twice when a child
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* crashes. So we don't try to Assert anything about the state.
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*/
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result = (PMSignalState->PMChildFlags[slot] == PM_CHILD_ASSIGNED);
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PMSignalState->PMChildFlags[slot] = PM_CHILD_UNUSED;
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return result;
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}
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/*
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* IsPostmasterChildWalSender - check if given slot is in use by a
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* walsender process.
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*/
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bool
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IsPostmasterChildWalSender(int slot)
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{
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Assert(slot > 0 && slot <= PMSignalState->num_child_flags);
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slot--;
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if (PMSignalState->PMChildFlags[slot] == PM_CHILD_WALSENDER)
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return true;
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else
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return false;
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}
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/*
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* MarkPostmasterChildActive - mark a postmaster child as about to begin
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* actively using shared memory. This is called in the child process.
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*/
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void
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MarkPostmasterChildActive(void)
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{
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int slot = MyPMChildSlot;
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Assert(slot > 0 && slot <= PMSignalState->num_child_flags);
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slot--;
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Assert(PMSignalState->PMChildFlags[slot] == PM_CHILD_ASSIGNED);
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PMSignalState->PMChildFlags[slot] = PM_CHILD_ACTIVE;
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}
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/*
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* MarkPostmasterChildWalSender - mark a postmaster child as a WAL sender
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* process. This is called in the child process, sometime after marking the
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* child as active.
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*/
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void
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MarkPostmasterChildWalSender(void)
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{
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int slot = MyPMChildSlot;
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Assert(am_walsender);
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Assert(slot > 0 && slot <= PMSignalState->num_child_flags);
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slot--;
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Assert(PMSignalState->PMChildFlags[slot] == PM_CHILD_ACTIVE);
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PMSignalState->PMChildFlags[slot] = PM_CHILD_WALSENDER;
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}
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/*
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* MarkPostmasterChildInactive - mark a postmaster child as done using
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* shared memory. This is called in the child process.
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*/
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void
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MarkPostmasterChildInactive(void)
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{
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int slot = MyPMChildSlot;
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Assert(slot > 0 && slot <= PMSignalState->num_child_flags);
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slot--;
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Assert(PMSignalState->PMChildFlags[slot] == PM_CHILD_ACTIVE ||
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PMSignalState->PMChildFlags[slot] == PM_CHILD_WALSENDER);
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PMSignalState->PMChildFlags[slot] = PM_CHILD_ASSIGNED;
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}
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/*
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* PostmasterIsAliveInternal - check whether postmaster process is still alive
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*
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* This is the slow path of PostmasterIsAlive(), where the caller has already
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* checked 'postmaster_possibly_dead'. (On platforms that don't support
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* a signal for parent death, PostmasterIsAlive() is just an alias for this.)
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*/
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bool
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PostmasterIsAliveInternal(void)
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{
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#ifdef USE_POSTMASTER_DEATH_SIGNAL
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/*
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* Reset the flag before checking, so that we don't miss a signal if
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* postmaster dies right after the check. If postmaster was indeed dead,
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* we'll re-arm it before returning to caller.
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*/
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postmaster_possibly_dead = false;
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#endif
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#ifndef WIN32
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{
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char c;
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ssize_t rc;
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rc = read(postmaster_alive_fds[POSTMASTER_FD_WATCH], &c, 1);
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/*
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* In the usual case, the postmaster is still alive, and there is no
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* data in the pipe.
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*/
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if (rc < 0 && (errno == EAGAIN || errno == EWOULDBLOCK))
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return true;
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else
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{
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/*
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* Postmaster is dead, or something went wrong with the read()
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* call.
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*/
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#ifdef USE_POSTMASTER_DEATH_SIGNAL
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postmaster_possibly_dead = true;
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#endif
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if (rc < 0)
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elog(FATAL, "read on postmaster death monitoring pipe failed: %m");
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else if (rc > 0)
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elog(FATAL, "unexpected data in postmaster death monitoring pipe");
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return false;
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}
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}
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#else /* WIN32 */
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if (WaitForSingleObject(PostmasterHandle, 0) == WAIT_TIMEOUT)
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return true;
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else
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{
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#ifdef USE_POSTMASTER_DEATH_SIGNAL
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postmaster_possibly_dead = true;
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#endif
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return false;
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}
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#endif /* WIN32 */
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}
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/*
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* PostmasterDeathSignalInit - request signal on postmaster death if possible
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*/
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void
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PostmasterDeathSignalInit(void)
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{
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#ifdef USE_POSTMASTER_DEATH_SIGNAL
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int signum = POSTMASTER_DEATH_SIGNAL;
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/* Register our signal handler. */
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pqsignal(signum, postmaster_death_handler);
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/* Request a signal on parent exit. */
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#if defined(PR_SET_PDEATHSIG)
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if (prctl(PR_SET_PDEATHSIG, signum) < 0)
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elog(ERROR, "could not request parent death signal: %m");
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#elif defined(PROC_PDEATHSIG_CTL)
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if (procctl(P_PID, 0, PROC_PDEATHSIG_CTL, &signum) < 0)
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elog(ERROR, "could not request parent death signal: %m");
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#else
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#error "USE_POSTMASTER_DEATH_SIGNAL set, but there is no mechanism to request the signal"
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#endif
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/*
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* Just in case the parent was gone already and we missed it, we'd better
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* check the slow way on the first call.
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*/
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postmaster_possibly_dead = true;
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#endif /* USE_POSTMASTER_DEATH_SIGNAL */
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}
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