custom_signals_16.0.patch

diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index c85cb5cc18..37ae4b3759 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -6,6 +6,7 @@
  *
  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
+ * Portions Copyright (c) 2024, Postgres Professional
  *
  * IDENTIFICATION
  *	  src/backend/storage/ipc/procsignal.c
@@ -97,6 +98,13 @@ typedef struct
 #define BARRIER_CLEAR_BIT(flags, type) \
 	((flags) &= ~(((uint32) 1) << (uint32) (type)))
 
+#define IsCustomProcSignalReason(reason) \
+	((reason) >= PROCSIG_CUSTOM_1 && (reason) <= PROCSIG_CUSTOM_N)
+
+static bool CustomSignalPendings[NUM_CUSTOM_PROCSIGNALS];
+static bool CustomSignalProcessing[NUM_CUSTOM_PROCSIGNALS];
+static ProcSignalHandler_type CustomInterruptHandlers[NUM_CUSTOM_PROCSIGNALS];
+
 static ProcSignalHeader *ProcSignal = NULL;
 static ProcSignalSlot *MyProcSignalSlot = NULL;
 
@@ -104,6 +112,8 @@ static bool CheckProcSignal(ProcSignalReason reason);
 static void CleanupProcSignalState(int status, Datum arg);
 static void ResetProcSignalBarrierBits(uint32 flags);
 
+static void CheckAndSetCustomSignalInterrupts(void);
+
 /*
  * ProcSignalShmemSize
  *		Compute space needed for ProcSignal's shared memory
@@ -247,6 +257,36 @@ CleanupProcSignalState(int status, Datum arg)
 	slot->pss_pid = 0;
 }
 
+/*
+ * RegisterCustomProcSignalHandler
+ *		Assign specific handler of custom process signal with new
+ *		ProcSignalReason key.
+ *
+ * This function has to be called in _PG_init function of extensions at the
+ * stage of loading shared preloaded libraries. Otherwise it throws fatal error.
+ *
+ * Return INVALID_PROCSIGNAL if all slots for custom signals are occupied.
+ */
+ProcSignalReason
+RegisterCustomProcSignalHandler(ProcSignalHandler_type handler)
+{
+	ProcSignalReason reason;
+
+	if (!process_shared_preload_libraries_in_progress)
+		ereport(FATAL, (errcode(ERRCODE_INTERNAL_ERROR),
+						errmsg("cannot register custom signal after startup")));
+
+	/* Iterate through custom signal slots to find a free one */
+	for (reason = PROCSIG_CUSTOM_1; reason <= PROCSIG_CUSTOM_N; reason++)
+		if (!CustomInterruptHandlers[reason - PROCSIG_CUSTOM_1])
+		{
+			CustomInterruptHandlers[reason - PROCSIG_CUSTOM_1] = handler;
+			return reason;
+		}
+
+	return INVALID_PROCSIGNAL;
+}
+
 /*
  * SendProcSignal
  *		Send a signal to a Postgres process
@@ -682,7 +722,72 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	CheckAndSetCustomSignalInterrupts();
+
 	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
+
+/*
+ * Handle receipt of an interrupt indicating any of custom process signals.
+ */
+static void
+CheckAndSetCustomSignalInterrupts()
+{
+	ProcSignalReason	reason;
+
+	for (reason = PROCSIG_CUSTOM_1; reason <= PROCSIG_CUSTOM_N; reason++)
+	{
+		if (CheckProcSignal(reason))
+		{
+
+			/* set interrupt flags */
+			InterruptPending = true;
+			CustomSignalPendings[reason - PROCSIG_CUSTOM_1] = true;
+		}
+	}
+
+	SetLatch(MyLatch);
+}
+
+/*
+ * CheckAndHandleCustomSignals
+ *		Check custom signal flags and call handler assigned to that signal
+ *		if it is not NULL
+ *
+ * This function is called within CHECK_FOR_INTERRUPTS if interrupt occurred.
+ */
+void
+CheckAndHandleCustomSignals(void)
+{
+	int i;
+
+	/*
+	 * This is invoked from ProcessInterrupts(), and since some of the
+	 * functions it calls contain CHECK_FOR_INTERRUPTS(), there is a potential
+	 * for recursive calls if more signals are received while this runs, so
+	 * let's block interrupts until done.
+	 */
+	HOLD_INTERRUPTS();
+
+	/* Check on expiring of custom signals and call its handlers if exist */
+	for (i = 0; i < NUM_CUSTOM_PROCSIGNALS; i++)
+	{
+		if (!CustomSignalProcessing[i] && CustomSignalPendings[i])
+		{
+			ProcSignalHandler_type  handler;
+
+			CustomSignalPendings[i] = false;
+			handler = CustomInterruptHandlers[i];
+			if (handler != NULL)
+			{
+				CustomSignalProcessing[i] = true;
+				handler();
+				CustomSignalProcessing[i] = false;
+			}
+		}
+	}
+
+	RESUME_INTERRUPTS();
+}
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 36cc99ec9c..a3acce427a 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3442,6 +3442,8 @@ ProcessInterrupts(void)
 	if (ParallelMessagePending)
 		HandleParallelMessages();
 
+	CheckAndHandleCustomSignals();
+
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
 
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 2f52100b00..0e31a5771e 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -6,6 +6,7 @@
  *
  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
+ * Portions Copyright (c) 2024, Postgres Professional
  *
  * src/include/storage/procsignal.h
  *
@@ -17,6 +18,8 @@
 #include "storage/backendid.h"
 
 
+#define NUM_CUSTOM_PROCSIGNALS 64
+
 /*
  * Reasons for signaling a Postgres child process (a backend or an auxiliary
  * process, like checkpointer).  We can cope with concurrent signals for different
@@ -29,6 +32,8 @@
  */
 typedef enum
 {
+	INVALID_PROCSIGNAL = -1,	/* Must be first */
+
 	PROCSIG_CATCHUP_INTERRUPT,	/* sinval catchup interrupt */
 	PROCSIG_NOTIFY_INTERRUPT,	/* listen/notify interrupt */
 	PROCSIG_PARALLEL_MESSAGE,	/* message from cooperating parallel backend */
@@ -46,6 +51,14 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_CUSTOM_1,
+	/*
+	 * PROCSIG_CUSTOM_2,
+	 * ...,
+	 * PROCSIG_CUSTOM_N-1,
+	 */
+	PROCSIG_CUSTOM_N = PROCSIG_CUSTOM_1 + NUM_CUSTOM_PROCSIGNALS - 1,
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
@@ -54,6 +67,9 @@ typedef enum
 	PROCSIGNAL_BARRIER_SMGRRELEASE	/* ask smgr to close files */
 } ProcSignalBarrierType;
 
+/* Handler of custom process signal */
+typedef void (*ProcSignalHandler_type) (void);
+
 /*
  * prototypes for functions in procsignal.c
  */
@@ -61,12 +77,15 @@ extern Size ProcSignalShmemSize(void);
 extern void ProcSignalShmemInit(void);
 
 extern void ProcSignalInit(int pss_idx);
+extern ProcSignalReason
+	RegisterCustomProcSignalHandler(ProcSignalHandler_type handler);
 extern int	SendProcSignal(pid_t pid, ProcSignalReason reason,
 						   BackendId backendId);
 
 extern uint64 EmitProcSignalBarrier(ProcSignalBarrierType type);
 extern void WaitForProcSignalBarrier(uint64 generation);
 extern void ProcessProcSignalBarrier(void);
+extern void CheckAndHandleCustomSignals(void);
 
 extern void procsignal_sigusr1_handler(SIGNAL_ARGS);