1 files changed, 522 insertions, 0 deletions
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
new file mode 100644
index 00000000000..d868602de2e
--- /dev/null
+++ b/src/backend/port/sysv_sema.c
@@ -0,0 +1,522 @@
+/*-------------------------------------------------------------------------
+ *
+ * sysv_sema.c
+ *	  Implement PGSemaphores using SysV semaphore facilities
+ *
+ *
+ * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  $Header: /cvsroot/pgsql/src/backend/port/sysv_sema.c,v 1.1 2002/05/05 00:03:28 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/file.h>
+#include <sys/types.h>
+#ifdef HAVE_SYS_IPC_H
+#include <sys/ipc.h>
+#endif
+#ifdef HAVE_SYS_SEM_H
+#include <sys/sem.h>
+#endif
+#ifdef HAVE_KERNEL_OS_H
+#include <kernel/OS.h>
+#endif
+
+#include "miscadmin.h"
+#include "storage/ipc.h"
+#include "storage/pg_sema.h"
+
+
+#ifndef HAVE_UNION_SEMUN
+union semun
+{
+	int			val;
+	struct semid_ds *buf;
+	unsigned short *array;
+};
+#endif
+
+typedef uint32 IpcSemaphoreKey; /* semaphore key passed to semget(2) */
+typedef int IpcSemaphoreId;		/* semaphore ID returned by semget(2) */
+
+/*
+ * SEMAS_PER_SET is the number of useful semaphores in each semaphore set
+ * we allocate.  It must be *less than* your kernel's SEMMSL (max semaphores
+ * per set) parameter, which is often around 25.  (Less than, because we
+ * allocate one extra sema in each set for identification purposes.)
+ */
+#define SEMAS_PER_SET	16
+
+#define IPCProtection	(0600)	/* access/modify by user only */
+
+#define PGSemaMagic		537		/* must be less than SEMVMX */
+
+
+static IpcSemaphoreId *mySemaSets; /* IDs of sema sets acquired so far */
+static int	numSemaSets;		/* number of sema sets acquired so far */
+static int	maxSemaSets;		/* allocated size of mySemaSets array */
+static IpcSemaphoreKey nextSemaKey; /* next key to try using */
+static int	nextSemaNumber;		/* next free sem num in last sema set */
+
+
+static IpcSemaphoreId InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey,
+												 int numSems);
+static void IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum,
+								   int value);
+static void IpcSemaphoreKill(IpcSemaphoreId semId);
+static int IpcSemaphoreGetValue(IpcSemaphoreId semId, int semNum);
+static pid_t IpcSemaphoreGetLastPID(IpcSemaphoreId semId, int semNum);
+static IpcSemaphoreId IpcSemaphoreCreate(int numSems);
+static void ReleaseSemaphores(int status, Datum arg);
+
+
+/*
+ * InternalIpcSemaphoreCreate
+ *
+ * Attempt to create a new semaphore set with the specified key.
+ * Will fail (return -1) if such a set already exists.
+ *
+ * If we fail with a failure code other than collision-with-existing-set,
+ * print out an error and abort.  Other types of errors suggest nonrecoverable
+ * problems.
+ */
+static IpcSemaphoreId
+InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems)
+{
+	int			semId;
+
+	semId = semget(semKey, numSems, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+	if (semId < 0)
+	{
+		/*
+		 * Fail quietly if error indicates a collision with existing set.
+		 * One would expect EEXIST, given that we said IPC_EXCL, but
+		 * perhaps we could get a permission violation instead?  Also,
+		 * EIDRM might occur if an old set is slated for destruction but
+		 * not gone yet.
+		 */
+		if (errno == EEXIST || errno == EACCES
+#ifdef EIDRM
+			|| errno == EIDRM
+#endif
+			)
+			return -1;
+
+		/*
+		 * Else complain and abort
+		 */
+		fprintf(stderr, "IpcSemaphoreCreate: semget(key=%d, num=%d, 0%o) failed: %s\n",
+				(int) semKey, numSems, (IPC_CREAT | IPC_EXCL | IPCProtection),
+				strerror(errno));
+
+		if (errno == ENOSPC)
+			fprintf(stderr,
+					"\nThis error does *not* mean that you have run out of disk space.\n"
+					"\n"
+					"It occurs when either the system limit for the maximum number of\n"
+					"semaphore sets (SEMMNI), or the system wide maximum number of\n"
+					"semaphores (SEMMNS), would be exceeded.  You need to raise the\n"
+					"respective kernel parameter.  Alternatively, reduce PostgreSQL's\n"
+					"consumption of semaphores by reducing its max_connections parameter\n"
+					"(currently %d).\n"
+					"\n"
+					"The PostgreSQL Administrator's Guide contains more information about\n"
+					"configuring your system for PostgreSQL.\n\n",
+					MaxBackends);
+
+		proc_exit(1);
+	}
+
+	return semId;
+}
+
+/*
+ * Initialize a semaphore to the specified value.
+ */
+static void
+IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum, int value)
+{
+	union semun semun;
+
+	semun.val = value;
+	if (semctl(semId, semNum, SETVAL, semun) < 0)
+	{
+		fprintf(stderr, "IpcSemaphoreInitialize: semctl(id=%d, %d, SETVAL, %d) failed: %s\n",
+				semId, semNum, value, strerror(errno));
+
+		if (errno == ERANGE)
+			fprintf(stderr,
+					"You possibly need to raise your kernel's SEMVMX value to be at least\n"
+					"%d.  Look into the PostgreSQL documentation for details.\n",
+					value);
+
+		proc_exit(1);
+	}
+}
+
+/*
+ * IpcSemaphoreKill(semId)	- removes a semaphore set
+ */
+static void
+IpcSemaphoreKill(IpcSemaphoreId semId)
+{
+	union semun semun;
+
+	semun.val = 0;				/* unused, but keep compiler quiet */
+
+	if (semctl(semId, 0, IPC_RMID, semun) < 0)
+		fprintf(stderr, "IpcSemaphoreKill: semctl(%d, 0, IPC_RMID, ...) failed: %s\n",
+				semId, strerror(errno));
+
+	/*
+	 * We used to report a failure via elog(WARNING), but that's pretty
+	 * pointless considering any client has long since disconnected ...
+	 */
+}
+
+/* Get the current value (semval) of the semaphore */
+static int
+IpcSemaphoreGetValue(IpcSemaphoreId semId, int semNum)
+{
+	union semun dummy;			/* for Solaris */
+
+	dummy.val = 0;				/* unused */
+
+	return semctl(semId, semNum, GETVAL, dummy);
+}
+
+/* Get the PID of the last process to do semop() on the semaphore */
+static pid_t
+IpcSemaphoreGetLastPID(IpcSemaphoreId semId, int semNum)
+{
+	union semun dummy;			/* for Solaris */
+
+	dummy.val = 0;				/* unused */
+
+	return semctl(semId, semNum, GETPID, dummy);
+}
+
+
+/*
+ * Create a semaphore set with the given number of useful semaphores
+ * (an additional sema is actually allocated to serve as identifier).
+ * Dead Postgres sema sets are recycled if found, but we do not fail
+ * upon collision with non-Postgres sema sets.
+ *
+ * The idea here is to detect and re-use keys that may have been assigned
+ * by a crashed postmaster or backend.
+ */
+static IpcSemaphoreId
+IpcSemaphoreCreate(int numSems)
+{
+	IpcSemaphoreId semId;
+	union semun semun;
+	PGSemaphoreData mysema;
+
+	/* Loop till we find a free IPC key */
+	for (nextSemaKey++; ; nextSemaKey++)
+	{
+		pid_t		creatorPID;
+
+		/* Try to create new semaphore set */
+		semId = InternalIpcSemaphoreCreate(nextSemaKey, numSems + 1);
+		if (semId >= 0)
+			break;				/* successful create */
+
+		/* See if it looks to be leftover from a dead Postgres process */
+		semId = semget(nextSemaKey, numSems + 1, 0);
+		if (semId < 0)
+			continue;			/* failed: must be some other app's */
+		if (IpcSemaphoreGetValue(semId, numSems) != PGSemaMagic)
+			continue;			/* sema belongs to a non-Postgres app */
+
+		/*
+		 * If the creator PID is my own PID or does not belong to any
+		 * extant process, it's safe to zap it.
+		 */
+		creatorPID = IpcSemaphoreGetLastPID(semId, numSems);
+		if (creatorPID <= 0)
+			continue;			/* oops, GETPID failed */
+		if (creatorPID != getpid())
+		{
+			if (kill(creatorPID, 0) == 0 ||
+				errno != ESRCH)
+				continue;		/* sema belongs to a live process */
+		}
+
+		/*
+		 * The sema set appears to be from a dead Postgres process, or
+		 * from a previous cycle of life in this same process.	Zap it, if
+		 * possible.  This probably shouldn't fail, but if it does, assume
+		 * the sema set belongs to someone else after all, and continue
+		 * quietly.
+		 */
+		semun.val = 0;			/* unused, but keep compiler quiet */
+		if (semctl(semId, 0, IPC_RMID, semun) < 0)
+			continue;
+
+		/*
+		 * Now try again to create the sema set.
+		 */
+		semId = InternalIpcSemaphoreCreate(nextSemaKey, numSems + 1);
+		if (semId >= 0)
+			break;				/* successful create */
+
+		/*
+		 * Can only get here if some other process managed to create the
+		 * same sema key before we did.  Let him have that one, loop
+		 * around to try next key.
+		 */
+	}
+
+	/*
+	 * OK, we created a new sema set.  Mark it as created by this process.
+	 * We do this by setting the spare semaphore to PGSemaMagic-1 and then
+	 * incrementing it with semop().  That leaves it with value
+	 * PGSemaMagic and sempid referencing this process.
+	 */
+	IpcSemaphoreInitialize(semId, numSems, PGSemaMagic - 1);
+	mysema.semId = semId;
+	mysema.semNum = numSems;
+	PGSemaphoreUnlock(&mysema);
+
+	return semId;
+}
+
+
+/*
+ * PGReserveSemaphores --- initialize semaphore support
+ *
+ * This is called during postmaster start or shared memory reinitialization.
+ * It should do whatever is needed to be able to support up to maxSemas
+ * subsequent PGSemaphoreCreate calls.  Also, if any system resources
+ * are acquired here or in PGSemaphoreCreate, register an on_shmem_exit
+ * callback to release them.
+ *
+ * The port number is passed for possible use as a key (for SysV, we use
+ * it to generate the starting semaphore key).  In a standalone backend,
+ * zero will be passed.
+ *
+ * In the SysV implementation, we acquire semaphore sets on-demand; the
+ * maxSemas parameter is just used to size the array that keeps track of
+ * acquired sets for subsequent releasing.
+ */
+void
+PGReserveSemaphores(int maxSemas, int port)
+{
+	maxSemaSets = (maxSemas + SEMAS_PER_SET-1) / SEMAS_PER_SET;
+	mySemaSets = (IpcSemaphoreId *)
+		malloc(maxSemaSets * sizeof(IpcSemaphoreId));
+	if (mySemaSets == NULL)
+		elog(PANIC, "Out of memory in PGReserveSemaphores");
+	numSemaSets = 0;
+	nextSemaKey = port * 1000;
+	nextSemaNumber = SEMAS_PER_SET;	/* force sema set alloc on 1st call */
+
+	on_shmem_exit(ReleaseSemaphores, 0);
+}
+
+/*
+ * Release semaphores at shutdown or shmem reinitialization
+ *
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+ReleaseSemaphores(int status, Datum arg)
+{
+	int			i;
+
+	for (i = 0; i < numSemaSets; i++)
+		IpcSemaphoreKill(mySemaSets[i]);
+	free(mySemaSets);
+}
+
+/*
+ * PGSemaphoreCreate
+ *
+ * Initialize a PGSemaphore structure to represent a sema with count 1
+ */
+void
+PGSemaphoreCreate(PGSemaphore sema)
+{
+	/* Can't do this in a backend, because static state is postmaster's */
+	Assert(!IsUnderPostmaster);
+
+	if (nextSemaNumber >= SEMAS_PER_SET)
+	{
+		/* Time to allocate another semaphore set */
+		if (numSemaSets >= maxSemaSets)
+			elog(PANIC, "PGSemaphoreCreate: too many semaphores created");
+		mySemaSets[numSemaSets] = IpcSemaphoreCreate(SEMAS_PER_SET);
+		numSemaSets++;
+		nextSemaNumber = 0;
+	}
+	/* Assign the next free semaphore in the current set */
+	sema->semId = mySemaSets[numSemaSets-1];
+	sema->semNum = nextSemaNumber++;
+	/* Initialize it to count 1 */
+	IpcSemaphoreInitialize(sema->semId, sema->semNum, 1);
+}
+
+/*
+ * PGSemaphoreReset
+ *
+ * Reset a previously-initialized PGSemaphore to have count 0
+ */
+void
+PGSemaphoreReset(PGSemaphore sema)
+{
+	IpcSemaphoreInitialize(sema->semId, sema->semNum, 0);
+}
+
+/*
+ * PGSemaphoreLock
+ *
+ * Lock a semaphore (decrement count), blocking if count would be < 0
+ */
+void
+PGSemaphoreLock(PGSemaphore sema, bool interruptOK)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = -1;			/* decrement */
+	sops.sem_flg = 0;
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we
+	 * returned from the operation prematurely because we were sent a
+	 * signal.	So we try and lock the semaphore again.
+	 *
+	 * Each time around the loop, we check for a cancel/die interrupt. We
+	 * assume that if such an interrupt comes in while we are waiting, it
+	 * will cause the semop() call to exit with errno == EINTR, so that we
+	 * will be able to service the interrupt (if not in a critical section
+	 * already).
+	 *
+	 * Once we acquire the lock, we do NOT check for an interrupt before
+	 * returning.  The caller needs to be able to record ownership of the
+	 * lock before any interrupt can be accepted.
+	 *
+	 * There is a window of a few instructions between CHECK_FOR_INTERRUPTS
+	 * and entering the semop() call.  If a cancel/die interrupt occurs in
+	 * that window, we would fail to notice it until after we acquire the
+	 * lock (or get another interrupt to escape the semop()).  We can
+	 * avoid this problem by temporarily setting ImmediateInterruptOK to
+	 * true before we do CHECK_FOR_INTERRUPTS; then, a die() interrupt in
+	 * this interval will execute directly.  However, there is a huge
+	 * pitfall: there is another window of a few instructions after the
+	 * semop() before we are able to reset ImmediateInterruptOK.  If an
+	 * interrupt occurs then, we'll lose control, which means that the
+	 * lock has been acquired but our caller did not get a chance to
+	 * record the fact. Therefore, we only set ImmediateInterruptOK if the
+	 * caller tells us it's OK to do so, ie, the caller does not need to
+	 * record acquiring the lock.  (This is currently true for lockmanager
+	 * locks, since the process that granted us the lock did all the
+	 * necessary state updates. It's not true for SysV semaphores used to
+	 * implement LW locks or emulate spinlocks --- but the wait time for
+	 * such locks should not be very long, anyway.)
+	 */
+	do
+	{
+		ImmediateInterruptOK = interruptOK;
+		CHECK_FOR_INTERRUPTS();
+		errStatus = semop(sema->semId, &sops, 1);
+		ImmediateInterruptOK = false;
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+	{
+		fprintf(stderr, "PGSemaphoreLock: semop(id=%d) failed: %s\n",
+				sema->semId, strerror(errno));
+		proc_exit(255);
+	}
+}
+
+/*
+ * PGSemaphoreUnlock
+ *
+ * Unlock a semaphore (increment count)
+ */
+void
+PGSemaphoreUnlock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = 1;			/* increment */
+	sops.sem_flg = 0;
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we
+	 * returned from the operation prematurely because we were sent a
+	 * signal.	So we try and unlock the semaphore again. Not clear this
+	 * can really happen, but might as well cope.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+	{
+		fprintf(stderr, "PGSemaphoreUnlock: semop(id=%d) failed: %s\n",
+				sema->semId, strerror(errno));
+		proc_exit(255);
+	}
+}
+
+/*
+ * PGSemaphoreTryLock
+ *
+ * Lock a semaphore only if able to do so without blocking
+ */
+bool
+PGSemaphoreTryLock(PGSemaphore sema)
+{
+	int			errStatus;
+	struct sembuf sops;
+
+	sops.sem_op = -1;			/* decrement */
+	sops.sem_flg = IPC_NOWAIT;	/* but don't block */
+	sops.sem_num = sema->semNum;
+
+	/*
+	 * Note: if errStatus is -1 and errno == EINTR then it means we
+	 * returned from the operation prematurely because we were sent a
+	 * signal.	So we try and lock the semaphore again.
+	 */
+	do
+	{
+		errStatus = semop(sema->semId, &sops, 1);
+	} while (errStatus < 0 && errno == EINTR);
+
+	if (errStatus < 0)
+	{
+		/* Expect EAGAIN or EWOULDBLOCK (platform-dependent) */
+#ifdef EAGAIN
+		if (errno == EAGAIN)
+			return false;		/* failed to lock it */
+#endif
+#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
+		if (errno == EWOULDBLOCK)
+			return false;		/* failed to lock it */
+#endif
+		/* Otherwise we got trouble */
+		fprintf(stderr, "PGSemaphoreTryLock: semop(id=%d) failed: %s\n",
+				sema->semId, strerror(errno));
+		proc_exit(255);
+	}
+
+	return true;
+}