1 /*-------------------------------------------------------------------------
4 * Routines for interprocess signalling
7 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
11 * src/backend/storage/ipc/procsignal.c
13 *-------------------------------------------------------------------------
20 #include "commands/async.h"
21 #include "miscadmin.h"
22 #include "storage/latch.h"
23 #include "storage/ipc.h"
24 #include "storage/proc.h"
25 #include "storage/shmem.h"
26 #include "storage/sinval.h"
27 #include "tcop/tcopprot.h"
31 * The SIGUSR1 signal is multiplexed to support signalling multiple event
32 * types. The specific reason is communicated via flags in shared memory.
33 * We keep a boolean flag for each possible "reason", so that different
34 * reasons can be signaled to a process concurrently. (However, if the same
35 * reason is signaled more than once nearly simultaneously, the process may
36 * observe it only once.)
38 * Each process that wants to receive signals registers its process ID
39 * in the ProcSignalSlots array. The array is indexed by backend ID to make
40 * slot allocation simple, and to avoid having to search the array when you
41 * know the backend ID of the process you're signalling. (We do support
42 * signalling without backend ID, but it's a bit less efficient.)
44 * The flags are actually declared as "volatile sig_atomic_t" for maximum
45 * portability. This should ensure that loads and stores of the flag
46 * values are atomic, allowing us to dispense with any explicit locking.
51 sig_atomic_t pss_signalFlags[NUM_PROCSIGNALS];
55 * We reserve a slot for each possible BackendId, plus one for each
56 * possible auxiliary process type. (This scheme assumes there is not
57 * more than one of any auxiliary process type at a time.)
59 #define NumProcSignalSlots (MaxBackends + NUM_AUXPROCTYPES)
62 * If this flag is set, the process latch will be set whenever SIGUSR1
63 * is received. This is useful when waiting for a signal from the postmaster.
64 * Spurious wakeups must be expected. Make sure that the flag is cleared
67 bool set_latch_on_sigusr1;
69 static ProcSignalSlot *ProcSignalSlots = NULL;
70 static volatile ProcSignalSlot *MyProcSignalSlot = NULL;
72 static bool CheckProcSignal(ProcSignalReason reason);
73 static void CleanupProcSignalState(int status, Datum arg);
77 * Compute space needed for procsignal's shared memory
80 ProcSignalShmemSize(void)
82 return NumProcSignalSlots * sizeof(ProcSignalSlot);
87 * Allocate and initialize procsignal's shared memory
90 ProcSignalShmemInit(void)
92 Size size = ProcSignalShmemSize();
95 ProcSignalSlots = (ProcSignalSlot *)
96 ShmemInitStruct("ProcSignalSlots", size, &found);
98 /* If we're first, set everything to zeroes */
100 MemSet(ProcSignalSlots, 0, size);
105 * Register the current process in the procsignal array
107 * The passed index should be my BackendId if the process has one,
108 * or MaxBackends + aux process type if not.
111 ProcSignalInit(int pss_idx)
113 volatile ProcSignalSlot *slot;
115 Assert(pss_idx >= 1 && pss_idx <= NumProcSignalSlots);
117 slot = &ProcSignalSlots[pss_idx - 1];
120 if (slot->pss_pid != 0)
121 elog(LOG, "process %d taking over ProcSignal slot %d, but it's not empty",
124 /* Clear out any leftover signal reasons */
125 MemSet(slot->pss_signalFlags, 0, NUM_PROCSIGNALS * sizeof(sig_atomic_t));
127 /* Mark slot with my PID */
128 slot->pss_pid = MyProcPid;
130 /* Remember slot location for CheckProcSignal */
131 MyProcSignalSlot = slot;
133 /* Set up to release the slot on process exit */
134 on_shmem_exit(CleanupProcSignalState, Int32GetDatum(pss_idx));
138 * CleanupProcSignalState
139 * Remove current process from ProcSignalSlots
141 * This function is called via on_shmem_exit() during backend shutdown.
144 CleanupProcSignalState(int status, Datum arg)
146 int pss_idx = DatumGetInt32(arg);
147 volatile ProcSignalSlot *slot;
149 slot = &ProcSignalSlots[pss_idx - 1];
150 Assert(slot == MyProcSignalSlot);
153 if (slot->pss_pid != MyProcPid)
156 * don't ERROR here. We're exiting anyway, and don't want to get into
157 * infinite loop trying to exit
159 elog(LOG, "process %d releasing ProcSignal slot %d, but it contains %d",
160 MyProcPid, pss_idx, (int) slot->pss_pid);
161 return; /* XXX better to zero the slot anyway? */
169 * Send a signal to a Postgres process
171 * Providing backendId is optional, but it will speed up the operation.
173 * On success (a signal was sent), zero is returned.
174 * On error, -1 is returned, and errno is set (typically to ESRCH or EPERM).
176 * Not to be confused with ProcSendSignal
179 SendProcSignal(pid_t pid, ProcSignalReason reason, BackendId backendId)
181 volatile ProcSignalSlot *slot;
183 if (backendId != InvalidBackendId)
185 slot = &ProcSignalSlots[backendId - 1];
188 * Note: Since there's no locking, it's possible that the target
189 * process detaches from shared memory and exits right after this
190 * test, before we set the flag and send signal. And the signal slot
191 * might even be recycled by a new process, so it's remotely possible
192 * that we set a flag for a wrong process. That's OK, all the signals
193 * are such that no harm is done if they're mistakenly fired.
195 if (slot->pss_pid == pid)
197 /* Atomically set the proper flag */
198 slot->pss_signalFlags[reason] = true;
200 return kill(pid, SIGUSR1);
206 * BackendId not provided, so search the array using pid. We search
207 * the array back to front so as to reduce search overhead. Passing
208 * InvalidBackendId means that the target is most likely an auxiliary
209 * process, which will have a slot near the end of the array.
213 for (i = NumProcSignalSlots - 1; i >= 0; i--)
215 slot = &ProcSignalSlots[i];
217 if (slot->pss_pid == pid)
219 /* the above note about race conditions applies here too */
221 /* Atomically set the proper flag */
222 slot->pss_signalFlags[reason] = true;
224 return kill(pid, SIGUSR1);
234 * CheckProcSignal - check to see if a particular reason has been
235 * signaled, and clear the signal flag. Should be called after receiving
239 CheckProcSignal(ProcSignalReason reason)
241 volatile ProcSignalSlot *slot = MyProcSignalSlot;
245 /* Careful here --- don't clear flag if we haven't seen it set */
246 if (slot->pss_signalFlags[reason])
248 slot->pss_signalFlags[reason] = false;
257 * procsignal_sigusr1_handler - handle SIGUSR1 signal.
260 procsignal_sigusr1_handler(SIGNAL_ARGS)
262 int save_errno = errno;
264 if (CheckProcSignal(PROCSIG_CATCHUP_INTERRUPT))
265 HandleCatchupInterrupt();
267 if (CheckProcSignal(PROCSIG_NOTIFY_INTERRUPT))
268 HandleNotifyInterrupt();
270 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_DATABASE))
271 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_DATABASE);
273 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_TABLESPACE))
274 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_TABLESPACE);
276 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_LOCK))
277 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_LOCK);
279 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT))
280 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT);
282 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK))
283 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
285 if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
286 RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
288 if (set_latch_on_sigusr1)
289 SetLatch(&MyProc->procLatch);
291 latch_sigusr1_handler();