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Create an internal semaphore API that is not tied to SysV semaphores.
As proof of concept, provide an alternate implementation based on POSIX semaphores. Also push the SysV shared-memory implementation into a separate file so that it can be replaced conveniently.
This commit is contained in:
Tom Lane
400
src/backend/port/sysv_shmem.c
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400
src/backend/port/sysv_shmem.c
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/*-------------------------------------------------------------------------
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*
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* sysv_shmem.c
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* Implement shared memory using SysV facilities
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*
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* These routines represent a fairly thin layer on top of SysV shared
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* memory functionality.
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*
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* Portions Copyright (c) 1996-2001, 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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* $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.1 2002/05/05 00:03:28 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <errno.h>
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#include <signal.h>
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#include <unistd.h>
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#include <sys/file.h>
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#include <sys/types.h>
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#ifdef HAVE_SYS_IPC_H
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#include <sys/ipc.h>
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#endif
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#ifdef HAVE_SYS_SHM_H
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#include <sys/shm.h>
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#endif
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#ifdef HAVE_KERNEL_OS_H
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#include <kernel/OS.h>
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#endif
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#include "miscadmin.h"
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#include "storage/ipc.h"
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#include "storage/pg_shmem.h"
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typedef uint32 IpcMemoryKey; /* shared memory key passed to shmget(2) */
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typedef int IpcMemoryId; /* shared memory ID returned by shmget(2) */
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#define IPCProtection (0600) /* access/modify by user only */
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static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size);
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static void IpcMemoryDetach(int status, Datum shmaddr);
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static void IpcMemoryDelete(int status, Datum shmId);
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static void *PrivateMemoryCreate(uint32 size);
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static void PrivateMemoryDelete(int status, Datum memaddr);
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/*
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* InternalIpcMemoryCreate(memKey, size)
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*
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* Attempt to create a new shared memory segment with the specified key.
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* Will fail (return NULL) if such a segment already exists. If successful,
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* attach the segment to the current process and return its attached address.
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* On success, callbacks are registered with on_shmem_exit to detach and
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* delete the segment when on_shmem_exit is called.
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*
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* If we fail with a failure code other than collision-with-existing-segment,
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* print out an error and abort. Other types of errors are not recoverable.
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*/
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static void *
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InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size)
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{
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IpcMemoryId shmid;
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void *memAddress;
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shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
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if (shmid < 0)
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{
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/*
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* Fail quietly if error indicates a collision with existing
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* segment. One would expect EEXIST, given that we said IPC_EXCL,
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* but perhaps we could get a permission violation instead? Also,
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* EIDRM might occur if an old seg is slated for destruction but
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* not gone yet.
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*/
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if (errno == EEXIST || errno == EACCES
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#ifdef EIDRM
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|| errno == EIDRM
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#endif
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)
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return NULL;
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/*
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* Else complain and abort
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*/
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fprintf(stderr, "IpcMemoryCreate: shmget(key=%d, size=%u, 0%o) failed: %s\n",
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(int) memKey, size, (IPC_CREAT | IPC_EXCL | IPCProtection),
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strerror(errno));
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if (errno == EINVAL)
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fprintf(stderr,
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"\nThis error usually means that PostgreSQL's request for a shared memory\n"
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"segment exceeded your kernel's SHMMAX parameter. You can either\n"
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"reduce the request size or reconfigure the kernel with larger SHMMAX.\n"
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"To reduce the request size (currently %u bytes), reduce\n"
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"PostgreSQL's shared_buffers parameter (currently %d) and/or\n"
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"its max_connections parameter (currently %d).\n"
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"\n"
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"If the request size is already small, it's possible that it is less than\n"
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"your kernel's SHMMIN parameter, in which case raising the request size or\n"
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"reconfiguring SHMMIN is called for.\n"
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"\n"
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"The PostgreSQL Administrator's Guide contains more information about\n"
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"shared memory configuration.\n\n",
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size, NBuffers, MaxBackends);
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else if (errno == ENOMEM)
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fprintf(stderr,
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"\nThis error usually means that PostgreSQL's request for a shared\n"
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"memory segment exceeded available memory or swap space.\n"
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"To reduce the request size (currently %u bytes), reduce\n"
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"PostgreSQL's shared_buffers parameter (currently %d) and/or\n"
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"its max_connections parameter (currently %d).\n"
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"\n"
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"The PostgreSQL Administrator's Guide contains more information about\n"
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"shared memory configuration.\n\n",
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size, NBuffers, MaxBackends);
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else if (errno == ENOSPC)
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fprintf(stderr,
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"\nThis error does *not* mean that you have run out of disk space.\n"
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"\n"
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"It occurs either if all available shared memory IDs have been taken,\n"
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"in which case you need to raise the SHMMNI parameter in your kernel,\n"
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"or because the system's overall limit for shared memory has been\n"
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"reached. If you cannot increase the shared memory limit,\n"
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"reduce PostgreSQL's shared memory request (currently %u bytes),\n"
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"by reducing its shared_buffers parameter (currently %d) and/or\n"
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"its max_connections parameter (currently %d).\n"
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"\n"
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"The PostgreSQL Administrator's Guide contains more information about\n"
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"shared memory configuration.\n\n",
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size, NBuffers, MaxBackends);
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proc_exit(1);
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}
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/* Register on-exit routine to delete the new segment */
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on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
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/* OK, should be able to attach to the segment */
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#if defined(solaris) && defined(__sparc__)
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/* use intimate shared memory on SPARC Solaris */
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memAddress = shmat(shmid, 0, SHM_SHARE_MMU);
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#else
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memAddress = shmat(shmid, 0, 0);
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#endif
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if (memAddress == (void *) -1)
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{
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fprintf(stderr, "IpcMemoryCreate: shmat(id=%d) failed: %s\n",
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shmid, strerror(errno));
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proc_exit(1);
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}
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/* Register on-exit routine to detach new segment before deleting */
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on_shmem_exit(IpcMemoryDetach, PointerGetDatum(memAddress));
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/* Record key and ID in lockfile for data directory. */
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RecordSharedMemoryInLockFile((unsigned long) memKey,
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(unsigned long) shmid);
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return memAddress;
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}
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/****************************************************************************/
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/* IpcMemoryDetach(status, shmaddr) removes a shared memory segment */
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/* from process' address spaceq */
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/* (called as an on_shmem_exit callback, hence funny argument list) */
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/****************************************************************************/
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static void
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IpcMemoryDetach(int status, Datum shmaddr)
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{
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if (shmdt(DatumGetPointer(shmaddr)) < 0)
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fprintf(stderr, "IpcMemoryDetach: shmdt(%p) failed: %s\n",
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DatumGetPointer(shmaddr), strerror(errno));
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/*
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* We used to report a failure via elog(WARNING), but that's pretty
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* pointless considering any client has long since disconnected ...
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*/
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}
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/****************************************************************************/
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/* IpcMemoryDelete(status, shmId) deletes a shared memory segment */
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/* (called as an on_shmem_exit callback, hence funny argument list) */
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/****************************************************************************/
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static void
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IpcMemoryDelete(int status, Datum shmId)
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{
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if (shmctl(DatumGetInt32(shmId), IPC_RMID, (struct shmid_ds *) NULL) < 0)
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fprintf(stderr, "IpcMemoryDelete: shmctl(%d, %d, 0) failed: %s\n",
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DatumGetInt32(shmId), IPC_RMID, strerror(errno));
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/*
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* We used to report a failure via elog(WARNING), but that's pretty
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* pointless considering any client has long since disconnected ...
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*/
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}
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/*
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* PGSharedMemoryIsInUse
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*
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* Is a previously-existing shmem segment still existing and in use?
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*/
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bool
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PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
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{
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IpcMemoryId shmId = (IpcMemoryId) id2;
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struct shmid_ds shmStat;
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/*
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* We detect whether a shared memory segment is in use by seeing
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* whether it (a) exists and (b) has any processes are attached to it.
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*
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* If we are unable to perform the stat operation for a reason other than
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* nonexistence of the segment (most likely, because it doesn't belong
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* to our userid), assume it is in use.
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*/
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if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
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{
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/*
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* EINVAL actually has multiple possible causes documented in the
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* shmctl man page, but we assume it must mean the segment no
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* longer exists.
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*/
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if (errno == EINVAL)
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return false;
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/* Else assume segment is in use */
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return true;
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}
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/* If it has attached processes, it's in use */
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if (shmStat.shm_nattch != 0)
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return true;
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return false;
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}
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/* ----------------------------------------------------------------
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* private memory support
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*
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* Rather than allocating shmem segments with IPC_PRIVATE key, we
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* just malloc() the requested amount of space. This code emulates
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* the needed shmem functions.
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* ----------------------------------------------------------------
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*/
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static void *
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PrivateMemoryCreate(uint32 size)
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{
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void *memAddress;
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memAddress = malloc(size);
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if (!memAddress)
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{
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fprintf(stderr, "PrivateMemoryCreate: malloc(%u) failed\n", size);
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proc_exit(1);
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}
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MemSet(memAddress, 0, size); /* keep Purify quiet */
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/* Register on-exit routine to release storage */
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on_shmem_exit(PrivateMemoryDelete, PointerGetDatum(memAddress));
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return memAddress;
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}
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static void
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PrivateMemoryDelete(int status, Datum memaddr)
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{
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free(DatumGetPointer(memaddr));
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}
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/*
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* PGSharedMemoryCreate
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*
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* Create a shared memory segment of the given size and initialize its
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* standard header. Also, register an on_shmem_exit callback to release
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* the storage.
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*
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* Dead Postgres segments are recycled if found, but we do not fail upon
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* collision with non-Postgres shmem segments. The idea here is to detect and
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* re-use keys that may have been assigned by a crashed postmaster or backend.
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*
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* The port number is passed for possible use as a key (for SysV, we use
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* it to generate the starting shmem key). In a standalone backend,
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* zero will be passed.
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*/
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PGShmemHeader *
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PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
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{
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IpcMemoryKey NextShmemSegID;
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void *memAddress;
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PGShmemHeader *hdr;
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/* Room for a header? */
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Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
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/* Loop till we find a free IPC key */
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NextShmemSegID = port * 1000;
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for (NextShmemSegID++;; NextShmemSegID++)
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{
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IpcMemoryId shmid;
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/* Special case if creating a private segment --- just malloc() it */
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if (makePrivate)
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{
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memAddress = PrivateMemoryCreate(size);
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break;
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}
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/* Try to create new segment */
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memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
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if (memAddress)
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break; /* successful create and attach */
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/* See if it looks to be leftover from a dead Postgres process */
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shmid = shmget(NextShmemSegID, sizeof(PGShmemHeader), 0);
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if (shmid < 0)
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continue; /* failed: must be some other app's */
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#if defined(solaris) && defined(__sparc__)
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/* use intimate shared memory on SPARC Solaris */
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memAddress = shmat(shmid, 0, SHM_SHARE_MMU);
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#else
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memAddress = shmat(shmid, 0, 0);
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#endif
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if (memAddress == (void *) -1)
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continue; /* failed: must be some other app's */
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hdr = (PGShmemHeader *) memAddress;
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if (hdr->magic != PGShmemMagic)
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{
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shmdt(memAddress);
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continue; /* segment belongs to a non-Postgres app */
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}
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/*
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* If the creator PID is my own PID or does not belong to any
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* extant process, it's safe to zap it.
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*/
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if (hdr->creatorPID != getpid())
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{
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if (kill(hdr->creatorPID, 0) == 0 ||
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errno != ESRCH)
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{
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shmdt(memAddress);
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continue; /* segment belongs to a live process */
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}
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}
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/*
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* The segment appears to be from a dead Postgres process, or from
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* a previous cycle of life in this same process. Zap it, if
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* possible. This probably shouldn't fail, but if it does, assume
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* the segment belongs to someone else after all, and continue
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* quietly.
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*/
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shmdt(memAddress);
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if (shmctl(shmid, IPC_RMID, (struct shmid_ds *) NULL) < 0)
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continue;
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/*
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* Now try again to create the segment.
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*/
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memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
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if (memAddress)
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break; /* successful create and attach */
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/*
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* Can only get here if some other process managed to create the
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* same shmem key before we did. Let him have that one, loop
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* around to try next key.
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*/
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}
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/*
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* OK, we created a new segment. Mark it as created by this process.
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* The order of assignments here is critical so that another Postgres
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* process can't see the header as valid but belonging to an invalid
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* PID!
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*/
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hdr = (PGShmemHeader *) memAddress;
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hdr->creatorPID = getpid();
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hdr->magic = PGShmemMagic;
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/*
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* Initialize space allocation status for segment.
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*/
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hdr->totalsize = size;
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hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
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return hdr;
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}
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Reference in New Issue
Block a user