greenplumn parallel 源码
greenplumn parallel 代码
文件路径：/src/backend/access/transam/parallel.c
/*-------------------------------------------------------------------------
*
* parallel.c
* Infrastructure for launching parallel workers
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/access/transam/parallel.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/nbtree.h"
#include "access/parallel.h"
#include "access/session.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/pg_enum.h"
#include "catalog/index.h"
#include "catalog/namespace.h"
#include "commands/async.h"
#include "executor/execParallel.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "libpq/pqmq.h"
#include "miscadmin.h"
#include "optimizer/optimizer.h"
#include "pgstat.h"
#include "storage/ipc.h"
#include "storage/predicate.h"
#include "storage/sinval.h"
#include "storage/spin.h"
#include "tcop/tcopprot.h"
#include "utils/combocid.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/relmapper.h"
#include "utils/snapmgr.h"
#include "utils/typcache.h"
/*
* We don't want to waste a lot of memory on an error queue which, most of
* the time, will process only a handful of small messages. However, it is
* desirable to make it large enough that a typical ErrorResponse can be sent
* without blocking. That way, a worker that errors out can write the whole
* message into the queue and terminate without waiting for the user backend.
*/
#define PARALLEL_ERROR_QUEUE_SIZE 16384
/* Magic number for parallel context TOC. */
#define PARALLEL_MAGIC 0x50477c7c
/*
* Magic numbers for per-context parallel state sharing. Higher-level code
* should use smaller values, leaving these very large ones for use by this
* module.
*/
#define PARALLEL_KEY_FIXED UINT64CONST(0xFFFFFFFFFFFF0001)
#define PARALLEL_KEY_ERROR_QUEUE UINT64CONST(0xFFFFFFFFFFFF0002)
#define PARALLEL_KEY_LIBRARY UINT64CONST(0xFFFFFFFFFFFF0003)
#define PARALLEL_KEY_GUC UINT64CONST(0xFFFFFFFFFFFF0004)
#define PARALLEL_KEY_COMBO_CID UINT64CONST(0xFFFFFFFFFFFF0005)
#define PARALLEL_KEY_TRANSACTION_SNAPSHOT UINT64CONST(0xFFFFFFFFFFFF0006)
#define PARALLEL_KEY_ACTIVE_SNAPSHOT UINT64CONST(0xFFFFFFFFFFFF0007)
#define PARALLEL_KEY_TRANSACTION_STATE UINT64CONST(0xFFFFFFFFFFFF0008)
#define PARALLEL_KEY_ENTRYPOINT UINT64CONST(0xFFFFFFFFFFFF0009)
#define PARALLEL_KEY_SESSION_DSM UINT64CONST(0xFFFFFFFFFFFF000A)
#define PARALLEL_KEY_REINDEX_STATE UINT64CONST(0xFFFFFFFFFFFF000B)
#define PARALLEL_KEY_RELMAPPER_STATE UINT64CONST(0xFFFFFFFFFFFF000C)
#define PARALLEL_KEY_ENUMBLACKLIST UINT64CONST(0xFFFFFFFFFFFF000D)
/* Fixed-size parallel state. */
typedef struct FixedParallelState
{
/* Fixed-size state that workers must restore. */
Oid database_id;
Oid authenticated_user_id;
Oid current_user_id;
Oid outer_user_id;
Oid temp_namespace_id;
Oid temp_toast_namespace_id;
int sec_context;
bool is_superuser;
PGPROC *parallel_master_pgproc;
pid_t parallel_master_pid;
BackendId parallel_master_backend_id;
TimestampTz xact_ts;
TimestampTz stmt_ts;
SerializableXactHandle serializable_xact_handle;
/* Mutex protects remaining fields. */
slock_t mutex;
/* Maximum XactLastRecEnd of any worker. */
XLogRecPtr last_xlog_end;
} FixedParallelState;
/*
* Our parallel worker number. We initialize this to -1, meaning that we are
* not a parallel worker. In parallel workers, it will be set to a value >= 0
* and < the number of workers before any user code is invoked; each parallel
* worker will get a different parallel worker number.
*/
int ParallelWorkerNumber = -1;
/* Is there a parallel message pending which we need to receive? */
volatile bool ParallelMessagePending = false;
/* Are we initializing a parallel worker? */
bool InitializingParallelWorker = false;
/* Pointer to our fixed parallel state. */
static FixedParallelState *MyFixedParallelState;
/* List of active parallel contexts. */
static dlist_head pcxt_list = DLIST_STATIC_INIT(pcxt_list);
/* Backend-local copy of data from FixedParallelState. */
static pid_t ParallelMasterPid;
/*
* List of internal parallel worker entry points. We need this for
* reasons explained in LookupParallelWorkerFunction(), below.
*/
static const struct
{
const char *fn_name;
parallel_worker_main_type fn_addr;
} InternalParallelWorkers[] =
{
{
"ParallelQueryMain", ParallelQueryMain
},
{
"_bt_parallel_build_main", _bt_parallel_build_main
}
};
/* Private functions. */
static void HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg);
static void WaitForParallelWorkersToExit(ParallelContext *pcxt);
static parallel_worker_main_type LookupParallelWorkerFunction(const char *libraryname, const char *funcname);
static void ParallelWorkerShutdown(int code, Datum arg);
/*
* Establish a new parallel context. This should be done after entering
* parallel mode, and (unless there is an error) the context should be
* destroyed before exiting the current subtransaction.
*/
ParallelContext *
CreateParallelContext(const char *library_name, const char *function_name,
int nworkers)
{
MemoryContext oldcontext;
ParallelContext *pcxt;
/* It is unsafe to create a parallel context if not in parallel mode. */
Assert(IsInParallelMode());
/* Number of workers should be non-negative. */
Assert(nworkers >= 0);
/* We might be running in a short-lived memory context. */
oldcontext = MemoryContextSwitchTo(TopTransactionContext);
/* Initialize a new ParallelContext. */
pcxt = palloc0(sizeof(ParallelContext));
pcxt->subid = GetCurrentSubTransactionId();
pcxt->nworkers = nworkers;
pcxt->library_name = pstrdup(library_name);
pcxt->function_name = pstrdup(function_name);
pcxt->error_context_stack = error_context_stack;
shm_toc_initialize_estimator(&pcxt->estimator);
dlist_push_head(&pcxt_list, &pcxt->node);
/* Restore previous memory context. */
MemoryContextSwitchTo(oldcontext);
return pcxt;
}
/*
* Establish the dynamic shared memory segment for a parallel context and
* copy state and other bookkeeping information that will be needed by
* parallel workers into it.
*/
void
InitializeParallelDSM(ParallelContext *pcxt)
{
MemoryContext oldcontext;
Size library_len = 0;
Size guc_len = 0;
Size combocidlen = 0;
Size tsnaplen = 0;
Size asnaplen = 0;
Size tstatelen = 0;
Size reindexlen = 0;
Size relmapperlen = 0;
Size enumblacklistlen = 0;
Size segsize = 0;
int i;
FixedParallelState *fps;
dsm_handle session_dsm_handle = DSM_HANDLE_INVALID;
Snapshot transaction_snapshot = GetTransactionSnapshot();
Snapshot active_snapshot = GetActiveSnapshot();
/* We might be running in a very short-lived memory context. */
oldcontext = MemoryContextSwitchTo(TopTransactionContext);
/* Allow space to store the fixed-size parallel state. */
shm_toc_estimate_chunk(&pcxt->estimator, sizeof(FixedParallelState));
shm_toc_estimate_keys(&pcxt->estimator, 1);
/*
* Normally, the user will have requested at least one worker process, but
* if by chance they have not, we can skip a bunch of things here.
*/
if (pcxt->nworkers > 0)
{
/* Get (or create) the per-session DSM segment's handle. */
session_dsm_handle = GetSessionDsmHandle();
/*
* If we weren't able to create a per-session DSM segment, then we can
* continue but we can't safely launch any workers because their
* record typmods would be incompatible so they couldn't exchange
* tuples.
*/
if (session_dsm_handle == DSM_HANDLE_INVALID)
pcxt->nworkers = 0;
}
if (pcxt->nworkers > 0)
{
/* Estimate space for various kinds of state sharing. */
library_len = EstimateLibraryStateSpace();
shm_toc_estimate_chunk(&pcxt->estimator, library_len);
guc_len = EstimateGUCStateSpace();
shm_toc_estimate_chunk(&pcxt->estimator, guc_len);
combocidlen = EstimateComboCIDStateSpace();
shm_toc_estimate_chunk(&pcxt->estimator, combocidlen);
tsnaplen = EstimateSnapshotSpace(transaction_snapshot);
shm_toc_estimate_chunk(&pcxt->estimator, tsnaplen);
asnaplen = EstimateSnapshotSpace(active_snapshot);
shm_toc_estimate_chunk(&pcxt->estimator, asnaplen);
tstatelen = EstimateTransactionStateSpace();
shm_toc_estimate_chunk(&pcxt->estimator, tstatelen);
shm_toc_estimate_chunk(&pcxt->estimator, sizeof(dsm_handle));
reindexlen = EstimateReindexStateSpace();
shm_toc_estimate_chunk(&pcxt->estimator, reindexlen);
relmapperlen = EstimateRelationMapSpace();
shm_toc_estimate_chunk(&pcxt->estimator, relmapperlen);
enumblacklistlen = EstimateEnumBlacklistSpace();
shm_toc_estimate_chunk(&pcxt->estimator, enumblacklistlen);
/* If you add more chunks here, you probably need to add keys. */
shm_toc_estimate_keys(&pcxt->estimator, 10);
/* Estimate space need for error queues. */
StaticAssertStmt(BUFFERALIGN(PARALLEL_ERROR_QUEUE_SIZE) ==
PARALLEL_ERROR_QUEUE_SIZE,
"parallel error queue size not buffer-aligned");
shm_toc_estimate_chunk(&pcxt->estimator,
mul_size(PARALLEL_ERROR_QUEUE_SIZE,
pcxt->nworkers));
shm_toc_estimate_keys(&pcxt->estimator, 1);
/* Estimate how much we'll need for the entrypoint info. */
shm_toc_estimate_chunk(&pcxt->estimator, strlen(pcxt->library_name) +
strlen(pcxt->function_name) + 2);
shm_toc_estimate_keys(&pcxt->estimator, 1);
}
/*
* Create DSM and initialize with new table of contents. But if the user
* didn't request any workers, then don't bother creating a dynamic shared
* memory segment; instead, just use backend-private memory.
*
* Also, if we can't create a dynamic shared memory segment because the
* maximum number of segments have already been created, then fall back to
* backend-private memory, and plan not to use any workers. We hope this
* won't happen very often, but it's better to abandon the use of
* parallelism than to fail outright.
*/
segsize = shm_toc_estimate(&pcxt->estimator);
if (pcxt->nworkers > 0)
pcxt->seg = dsm_create(segsize, DSM_CREATE_NULL_IF_MAXSEGMENTS);
if (pcxt->seg != NULL)
pcxt->toc = shm_toc_create(PARALLEL_MAGIC,
dsm_segment_address(pcxt->seg),
segsize);
else
{
pcxt->nworkers = 0;
pcxt->private_memory = MemoryContextAlloc(TopMemoryContext, segsize);
pcxt->toc = shm_toc_create(PARALLEL_MAGIC, pcxt->private_memory,
segsize);
}
/* Initialize fixed-size state in shared memory. */
fps = (FixedParallelState *)
shm_toc_allocate(pcxt->toc, sizeof(FixedParallelState));
fps->database_id = MyDatabaseId;
fps->authenticated_user_id = GetAuthenticatedUserId();
fps->outer_user_id = GetCurrentRoleId();
fps->is_superuser = session_auth_is_superuser;
GetUserIdAndSecContext(&fps->current_user_id, &fps->sec_context);
GetTempNamespaceState(&fps->temp_namespace_id,
&fps->temp_toast_namespace_id);
fps->parallel_master_pgproc = MyProc;
fps->parallel_master_pid = MyProcPid;
fps->parallel_master_backend_id = MyBackendId;
fps->xact_ts = GetCurrentTransactionStartTimestamp();
fps->stmt_ts = GetCurrentStatementStartTimestamp();
fps->serializable_xact_handle = ShareSerializableXact();
SpinLockInit(&fps->mutex);
fps->last_xlog_end = 0;
shm_toc_insert(pcxt->toc, PARALLEL_KEY_FIXED, fps);
/* We can skip the rest of this if we're not budgeting for any workers. */
if (pcxt->nworkers > 0)
{
char *libraryspace;
char *gucspace;
char *combocidspace;
char *tsnapspace;
char *asnapspace;
char *tstatespace;
char *reindexspace;
char *relmapperspace;
char *error_queue_space;
char *session_dsm_handle_space;
char *entrypointstate;
char *enumblacklistspace;
Size lnamelen;
/* Serialize shared libraries we have loaded. */
libraryspace = shm_toc_allocate(pcxt->toc, library_len);
SerializeLibraryState(library_len, libraryspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_LIBRARY, libraryspace);
/* Serialize GUC settings. */
gucspace = shm_toc_allocate(pcxt->toc, guc_len);
SerializeGUCState(guc_len, gucspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_GUC, gucspace);
/* Serialize combo CID state. */
combocidspace = shm_toc_allocate(pcxt->toc, combocidlen);
SerializeComboCIDState(combocidlen, combocidspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_COMBO_CID, combocidspace);
/* Serialize transaction snapshot and active snapshot. */
tsnapspace = shm_toc_allocate(pcxt->toc, tsnaplen);
SerializeSnapshot(transaction_snapshot, tsnapspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_TRANSACTION_SNAPSHOT,
tsnapspace);
asnapspace = shm_toc_allocate(pcxt->toc, asnaplen);
SerializeSnapshot(active_snapshot, asnapspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_ACTIVE_SNAPSHOT, asnapspace);
/* Provide the handle for per-session segment. */
session_dsm_handle_space = shm_toc_allocate(pcxt->toc,
sizeof(dsm_handle));
*(dsm_handle *) session_dsm_handle_space = session_dsm_handle;
shm_toc_insert(pcxt->toc, PARALLEL_KEY_SESSION_DSM,
session_dsm_handle_space);
/* Serialize transaction state. */
tstatespace = shm_toc_allocate(pcxt->toc, tstatelen);
SerializeTransactionState(tstatelen, tstatespace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_TRANSACTION_STATE, tstatespace);
/* Serialize reindex state. */
reindexspace = shm_toc_allocate(pcxt->toc, reindexlen);
SerializeReindexState(reindexlen, reindexspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_REINDEX_STATE, reindexspace);
/* Serialize relmapper state. */
relmapperspace = shm_toc_allocate(pcxt->toc, relmapperlen);
SerializeRelationMap(relmapperlen, relmapperspace);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_RELMAPPER_STATE,
relmapperspace);
/* Serialize enum blacklist state. */
enumblacklistspace = shm_toc_allocate(pcxt->toc, enumblacklistlen);
SerializeEnumBlacklist(enumblacklistspace, enumblacklistlen);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_ENUMBLACKLIST,
enumblacklistspace);
/* Allocate space for worker information. */
pcxt->worker = palloc0(sizeof(ParallelWorkerInfo) * pcxt->nworkers);
/*
* Establish error queues in dynamic shared memory.
*
* These queues should be used only for transmitting ErrorResponse,
* NoticeResponse, and NotifyResponse protocol messages. Tuple data
* should be transmitted via separate (possibly larger?) queues.
*/
error_queue_space =
shm_toc_allocate(pcxt->toc,
mul_size(PARALLEL_ERROR_QUEUE_SIZE,
pcxt->nworkers));
for (i = 0; i < pcxt->nworkers; ++i)
{
char *start;
shm_mq *mq;
start = error_queue_space + i * PARALLEL_ERROR_QUEUE_SIZE;
mq = shm_mq_create(start, PARALLEL_ERROR_QUEUE_SIZE);
shm_mq_set_receiver(mq, MyProc);
pcxt->worker[i].error_mqh = shm_mq_attach(mq, pcxt->seg, NULL);
}
shm_toc_insert(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, error_queue_space);
/*
* Serialize entrypoint information. It's unsafe to pass function
* pointers across processes, as the function pointer may be different
* in each process in EXEC_BACKEND builds, so we always pass library
* and function name. (We use library name "postgres" for functions
* in the core backend.)
*/
lnamelen = strlen(pcxt->library_name);
entrypointstate = shm_toc_allocate(pcxt->toc, lnamelen +
strlen(pcxt->function_name) + 2);
strcpy(entrypointstate, pcxt->library_name);
strcpy(entrypointstate + lnamelen + 1, pcxt->function_name);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_ENTRYPOINT, entrypointstate);
}
/* Restore previous memory context. */
MemoryContextSwitchTo(oldcontext);
}
/*
* Reinitialize the dynamic shared memory segment for a parallel context such
* that we could launch workers for it again.
*/
void
ReinitializeParallelDSM(ParallelContext *pcxt)
{
FixedParallelState *fps;
/* Wait for any old workers to exit. */
if (pcxt->nworkers_launched > 0)
{
WaitForParallelWorkersToFinish(pcxt);
WaitForParallelWorkersToExit(pcxt);
pcxt->nworkers_launched = 0;
if (pcxt->known_attached_workers)
{
pfree(pcxt->known_attached_workers);
pcxt->known_attached_workers = NULL;
pcxt->nknown_attached_workers = 0;
}
}
/* Reset a few bits of fixed parallel state to a clean state. */
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
fps->last_xlog_end = 0;
/* Recreate error queues (if they exist). */
if (pcxt->nworkers > 0)
{
char *error_queue_space;
int i;
error_queue_space =
shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, false);
for (i = 0; i < pcxt->nworkers; ++i)
{
char *start;
shm_mq *mq;
start = error_queue_space + i * PARALLEL_ERROR_QUEUE_SIZE;
mq = shm_mq_create(start, PARALLEL_ERROR_QUEUE_SIZE);
shm_mq_set_receiver(mq, MyProc);
pcxt->worker[i].error_mqh = shm_mq_attach(mq, pcxt->seg, NULL);
}
}
}
/*
* Launch parallel workers.
*/
void
LaunchParallelWorkers(ParallelContext *pcxt)
{
MemoryContext oldcontext;
BackgroundWorker worker;
int i;
bool any_registrations_failed = false;
/* Skip this if we have no workers. */
if (pcxt->nworkers == 0)
return;
/* We need to be a lock group leader. */
BecomeLockGroupLeader();
/* If we do have workers, we'd better have a DSM segment. */
Assert(pcxt->seg != NULL);
/* We might be running in a short-lived memory context. */
oldcontext = MemoryContextSwitchTo(TopTransactionContext);
/* Configure a worker. */
memset(&worker, 0, sizeof(worker));
snprintf(worker.bgw_name, BGW_MAXLEN, "parallel worker for PID %d",
MyProcPid);
snprintf(worker.bgw_type, BGW_MAXLEN, "parallel worker");
worker.bgw_flags =
BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION
| BGWORKER_CLASS_PARALLEL;
worker.bgw_start_time = BgWorkerStart_ConsistentState;
worker.bgw_restart_time = BGW_NEVER_RESTART;
sprintf(worker.bgw_library_name, "postgres");
sprintf(worker.bgw_function_name, "ParallelWorkerMain");
worker.bgw_main_arg = UInt32GetDatum(dsm_segment_handle(pcxt->seg));
worker.bgw_notify_pid = MyProcPid;
/*
* Start workers.
*
* The caller must be able to tolerate ending up with fewer workers than
* expected, so there is no need to throw an error here if registration
* fails. It wouldn't help much anyway, because registering the worker in
* no way guarantees that it will start up and initialize successfully.
*/
for (i = 0; i < pcxt->nworkers; ++i)
{
memcpy(worker.bgw_extra, &i, sizeof(int));
if (!any_registrations_failed &&
RegisterDynamicBackgroundWorker(&worker,
&pcxt->worker[i].bgwhandle))
{
shm_mq_set_handle(pcxt->worker[i].error_mqh,
pcxt->worker[i].bgwhandle);
pcxt->nworkers_launched++;
}
else
{
/*
* If we weren't able to register the worker, then we've bumped up
* against the max_worker_processes limit, and future
* registrations will probably fail too, so arrange to skip them.
* But we still have to execute this code for the remaining slots
* to make sure that we forget about the error queues we budgeted
* for those workers. Otherwise, we'll wait for them to start,
* but they never will.
*/
any_registrations_failed = true;
pcxt->worker[i].bgwhandle = NULL;
shm_mq_detach(pcxt->worker[i].error_mqh);
pcxt->worker[i].error_mqh = NULL;
}
}
/*
* Now that nworkers_launched has taken its final value, we can initialize
* known_attached_workers.
*/
if (pcxt->nworkers_launched > 0)
{
pcxt->known_attached_workers =
palloc0(sizeof(bool) * pcxt->nworkers_launched);
pcxt->nknown_attached_workers = 0;
}
/* Restore previous memory context. */
MemoryContextSwitchTo(oldcontext);
}
/*
* Wait for all workers to attach to their error queues, and throw an error if
* any worker fails to do this.
*
* Callers can assume that if this function returns successfully, then the
* number of workers given by pcxt->nworkers_launched have initialized and
* attached to their error queues. Whether or not these workers are guaranteed
* to still be running depends on what code the caller asked them to run;
* this function does not guarantee that they have not exited. However, it
* does guarantee that any workers which exited must have done so cleanly and
* after successfully performing the work with which they were tasked.
*
* If this function is not called, then some of the workers that were launched
* may not have been started due to a fork() failure, or may have exited during
* early startup prior to attaching to the error queue, so nworkers_launched
* cannot be viewed as completely reliable. It will never be less than the
* number of workers which actually started, but it might be more. Any workers
* that failed to start will still be discovered by
* WaitForParallelWorkersToFinish and an error will be thrown at that time,
* provided that function is eventually reached.
*
* In general, the leader process should do as much work as possible before
* calling this function. fork() failures and other early-startup failures
* are very uncommon, and having the leader sit idle when it could be doing
* useful work is undesirable. However, if the leader needs to wait for
* all of its workers or for a specific worker, it may want to call this
* function before doing so. If not, it must make some other provision for
* the failure-to-start case, lest it wait forever. On the other hand, a
* leader which never waits for a worker that might not be started yet, or
* at least never does so prior to WaitForParallelWorkersToFinish(), need not
* call this function at all.
*/
void
WaitForParallelWorkersToAttach(ParallelContext *pcxt)
{
int i;
/* Skip this if we have no launched workers. */
if (pcxt->nworkers_launched == 0)
return;
for (;;)
{
/*
* This will process any parallel messages that are pending and it may
* also throw an error propagated from a worker.
*/
CHECK_FOR_INTERRUPTS();
for (i = 0; i < pcxt->nworkers_launched; ++i)
{
BgwHandleStatus status;
shm_mq *mq;
int rc;
pid_t pid;
if (pcxt->known_attached_workers[i])
continue;
/*
* If error_mqh is NULL, then the worker has already exited
* cleanly.
*/
if (pcxt->worker[i].error_mqh == NULL)
{
pcxt->known_attached_workers[i] = true;
++pcxt->nknown_attached_workers;
continue;
}
status = GetBackgroundWorkerPid(pcxt->worker[i].bgwhandle, &pid);
if (status == BGWH_STARTED)
{
/* Has the worker attached to the error queue? */
mq = shm_mq_get_queue(pcxt->worker[i].error_mqh);
if (shm_mq_get_sender(mq) != NULL)
{
/* Yes, so it is known to be attached. */
pcxt->known_attached_workers[i] = true;
++pcxt->nknown_attached_workers;
}
}
else if (status == BGWH_STOPPED)
{
/*
* If the worker stopped without attaching to the error queue,
* throw an error.
*/
mq = shm_mq_get_queue(pcxt->worker[i].error_mqh);
if (shm_mq_get_sender(mq) == NULL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("parallel worker failed to initialize"),
errhint("More details may be available in the server log.")));
pcxt->known_attached_workers[i] = true;
++pcxt->nknown_attached_workers;
}
else
{
/*
* Worker not yet started, so we must wait. The postmaster
* will notify us if the worker's state changes. Our latch
* might also get set for some other reason, but if so we'll
* just end up waiting for the same worker again.
*/
rc = WaitLatch(MyLatch,
WL_LATCH_SET | WL_EXIT_ON_PM_DEATH,
-1, WAIT_EVENT_BGWORKER_STARTUP);
if (rc & WL_LATCH_SET)
ResetLatch(MyLatch);
}
}
/* If all workers are known to have started, we're done. */
if (pcxt->nknown_attached_workers >= pcxt->nworkers_launched)
{
Assert(pcxt->nknown_attached_workers == pcxt->nworkers_launched);
break;
}
}
}
/*
* Wait for all workers to finish computing.
*
* Even if the parallel operation seems to have completed successfully, it's
* important to call this function afterwards. We must not miss any errors
* the workers may have thrown during the parallel operation, or any that they
* may yet throw while shutting down.
*
* Also, we want to update our notion of XactLastRecEnd based on worker
* feedback.
*/
void
WaitForParallelWorkersToFinish(ParallelContext *pcxt)
{
for (;;)
{
bool anyone_alive = false;
int nfinished = 0;
int i;
/*
* This will process any parallel messages that are pending, which may
* change the outcome of the loop that follows. It may also throw an
* error propagated from a worker.
*/
CHECK_FOR_INTERRUPTS();
for (i = 0; i < pcxt->nworkers_launched; ++i)
{
/*
* If error_mqh is NULL, then the worker has already exited
* cleanly. If we have received a message through error_mqh from
* the worker, we know it started up cleanly, and therefore we're
* certain to be notified when it exits.
*/
if (pcxt->worker[i].error_mqh == NULL)
++nfinished;
else if (pcxt->known_attached_workers[i])
{
anyone_alive = true;
break;
}
}
if (!anyone_alive)
{
/* If all workers are known to have finished, we're done. */
if (nfinished >= pcxt->nworkers_launched)
{
Assert(nfinished == pcxt->nworkers_launched);
break;
}
/*
* We didn't detect any living workers, but not all workers are
* known to have exited cleanly. Either not all workers have
* launched yet, or maybe some of them failed to start or
* terminated abnormally.
*/
for (i = 0; i < pcxt->nworkers_launched; ++i)
{
pid_t pid;
shm_mq *mq;
/*
* If the worker is BGWH_NOT_YET_STARTED or BGWH_STARTED, we
* should just keep waiting. If it is BGWH_STOPPED, then
* further investigation is needed.
*/
if (pcxt->worker[i].error_mqh == NULL ||
pcxt->worker[i].bgwhandle == NULL ||
GetBackgroundWorkerPid(pcxt->worker[i].bgwhandle,
&pid) != BGWH_STOPPED)
continue;
/*
* Check whether the worker ended up stopped without ever
* attaching to the error queue. If so, the postmaster was
* unable to fork the worker or it exited without initializing
* properly. We must throw an error, since the caller may
* have been expecting the worker to do some work before
* exiting.
*/
mq = shm_mq_get_queue(pcxt->worker[i].error_mqh);
if (shm_mq_get_sender(mq) == NULL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("parallel worker failed to initialize"),
errhint("More details may be available in the server log.")));
/*
* The worker is stopped, but is attached to the error queue.
* Unless there's a bug somewhere, this will only happen when
* the worker writes messages and terminates after the
* CHECK_FOR_INTERRUPTS() near the top of this function and
* before the call to GetBackgroundWorkerPid(). In that case,
* or latch should have been set as well and the right things
* will happen on the next pass through the loop.
*/
}
}
(void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, -1,
WAIT_EVENT_PARALLEL_FINISH);
ResetLatch(MyLatch);
}
if (pcxt->toc != NULL)
{
FixedParallelState *fps;
fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
if (fps->last_xlog_end > XactLastRecEnd)
XactLastRecEnd = fps->last_xlog_end;
}
}
/*
* Wait for all workers to exit.
*
* This function ensures that workers have been completely shutdown. The
* difference between WaitForParallelWorkersToFinish and this function is
* that former just ensures that last message sent by worker backend is
* received by master backend whereas this ensures the complete shutdown.
*/
static void
WaitForParallelWorkersToExit(ParallelContext *pcxt)
{
int i;
/* Wait until the workers actually die. */
for (i = 0; i < pcxt->nworkers_launched; ++i)
{
BgwHandleStatus status;
if (pcxt->worker == NULL || pcxt->worker[i].bgwhandle == NULL)
continue;
status = WaitForBackgroundWorkerShutdown(pcxt->worker[i].bgwhandle);
/*
* If the postmaster kicked the bucket, we have no chance of cleaning
* up safely -- we won't be able to tell when our workers are actually
* dead. This doesn't necessitate a PANIC since they will all abort
* eventually, but we can't safely continue this session.
*/
if (status == BGWH_POSTMASTER_DIED)
ereport(FATAL,
(errcode(ERRCODE_ADMIN_SHUTDOWN),
errmsg("postmaster exited during a parallel transaction")));
/* Release memory. */
pfree(pcxt->worker[i].bgwhandle);
pcxt->worker[i].bgwhandle = NULL;
}
}
/*
* Destroy a parallel context.
*
* If expecting a clean exit, you should use WaitForParallelWorkersToFinish()
* first, before calling this function. When this function is invoked, any
* remaining workers are forcibly killed; the dynamic shared memory segment
* is unmapped; and we then wait (uninterruptibly) for the workers to exit.
*/
void
DestroyParallelContext(ParallelContext *pcxt)
{
int i;
/*
* Be careful about order of operations here! We remove the parallel
* context from the list before we do anything else; otherwise, if an
* error occurs during a subsequent step, we might try to nuke it again
* from AtEOXact_Parallel or AtEOSubXact_Parallel.
*/
dlist_delete(&pcxt->node);
/* Kill each worker in turn, and forget their error queues. */
if (pcxt->worker != NULL)
{
for (i = 0; i < pcxt->nworkers_launched; ++i)
{
if (pcxt->worker[i].error_mqh != NULL)
{
TerminateBackgroundWorker(pcxt->worker[i].bgwhandle);
shm_mq_detach(pcxt->worker[i].error_mqh);
pcxt->worker[i].error_mqh = NULL;
}
}
}
/*
* If we have allocated a shared memory segment, detach it. This will
* implicitly detach the error queues, and any other shared memory queues,
* stored there.
*/
if (pcxt->seg != NULL)
{
dsm_detach(pcxt->seg);
pcxt->seg = NULL;
}
/*
* If this parallel context is actually in backend-private memory rather
* than shared memory, free that memory instead.
*/
if (pcxt->private_memory != NULL)
{
pfree(pcxt->private_memory);
pcxt->private_memory = NULL;
}
/*
* We can't finish transaction commit or abort until all of the workers
* have exited. This means, in particular, that we can't respond to
* interrupts at this stage.
*/
HOLD_INTERRUPTS();
WaitForParallelWorkersToExit(pcxt);
RESUME_INTERRUPTS();
/* Free the worker array itself. */
if (pcxt->worker != NULL)
{
pfree(pcxt->worker);
pcxt->worker = NULL;
}
/* Free memory. */
pfree(pcxt->library_name);
pfree(pcxt->function_name);
pfree(pcxt);
}
/*
* Are there any parallel contexts currently active?
*/
bool
ParallelContextActive(void)
{
return !dlist_is_empty(&pcxt_list);
}
/*
* Handle receipt of an interrupt indicating a parallel worker message.
*
* Note: this is called within a signal handler! All we can do is set
* a flag that will cause the next CHECK_FOR_INTERRUPTS() to invoke
* HandleParallelMessages().
*/
void
HandleParallelMessageInterrupt(void)
{
InterruptPending = true;
ParallelMessagePending = true;
SetLatch(MyLatch);
}
/*
* Handle any queued protocol messages received from parallel workers.
*/
void
HandleParallelMessages(void)
{
dlist_iter iter;
MemoryContext oldcontext;
static MemoryContext hpm_context = NULL;
/*
* 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. It's
* unclear that recursive entry would be safe, and it doesn't seem useful
* even if it is safe, so let's block interrupts until done.
*/
HOLD_INTERRUPTS();
/*
* Moreover, CurrentMemoryContext might be pointing almost anywhere. We
* don't want to risk leaking data into long-lived contexts, so let's do
* our work here in a private context that we can reset on each use.
*/
if (hpm_context == NULL) /* first time through? */
hpm_context = AllocSetContextCreate(TopMemoryContext,
"HandleParallelMessages",
ALLOCSET_DEFAULT_SIZES);
else
MemoryContextReset(hpm_context);
oldcontext = MemoryContextSwitchTo(hpm_context);
/* OK to process messages. Reset the flag saying there are more to do. */
ParallelMessagePending = false;
dlist_foreach(iter, &pcxt_list)
{
ParallelContext *pcxt;
int i;
pcxt = dlist_container(ParallelContext, node, iter.cur);
if (pcxt->worker == NULL)
continue;
for (i = 0; i < pcxt->nworkers_launched; ++i)
{
/*
* Read as many messages as we can from each worker, but stop when
* either (1) the worker's error queue goes away, which can happen
* if we receive a Terminate message from the worker; or (2) no
* more messages can be read from the worker without blocking.
*/
while (pcxt->worker[i].error_mqh != NULL)
{
shm_mq_result res;
Size nbytes;
void *data;
res = shm_mq_receive(pcxt->worker[i].error_mqh, &nbytes,
&data, true);
if (res == SHM_MQ_WOULD_BLOCK)
break;
else if (res == SHM_MQ_SUCCESS)
{
StringInfoData msg;
initStringInfo(&msg);
appendBinaryStringInfo(&msg, data, nbytes);
HandleParallelMessage(pcxt, i, &msg);
pfree(msg.data);
}
else
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("lost connection to parallel worker")));
}
}
}
MemoryContextSwitchTo(oldcontext);
/* Might as well clear the context on our way out */
MemoryContextReset(hpm_context);
RESUME_INTERRUPTS();
}
/*
* Handle a single protocol message received from a single parallel worker.
*/
static void
HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg)
{
char msgtype;
if (pcxt->known_attached_workers != NULL &&
!pcxt->known_attached_workers[i])
{
pcxt->known_attached_workers[i] = true;
pcxt->nknown_attached_workers++;
}
msgtype = pq_getmsgbyte(msg);
switch (msgtype)
{
case 'K': /* BackendKeyData */
{
int32 pid = pq_getmsgint(msg, 4);
(void) pq_getmsgint(msg, 4); /* discard cancel key */
(void) pq_getmsgend(msg);
pcxt->worker[i].pid = pid;
break;
}
case 'E': /* ErrorResponse */
case 'N': /* NoticeResponse */
{
ErrorData edata;
ErrorContextCallback *save_error_context_stack;
/* Parse ErrorResponse or NoticeResponse. */
pq_parse_errornotice(msg, &edata);
/* Death of a worker isn't enough justification for suicide. */
edata.elevel = Min(edata.elevel, ERROR);
/*
* If desired, add a context line to show that this is a
* message propagated from a parallel worker. Otherwise, it
* can sometimes be confusing to understand what actually
* happened. (We don't do this in FORCE_PARALLEL_REGRESS mode
* because it causes test-result instability depending on
* whether a parallel worker is actually used or not.)
*/
if (force_parallel_mode != FORCE_PARALLEL_REGRESS)
{
if (edata.context)
edata.context = psprintf("%s\n%s", edata.context,
_("parallel worker"));
else
edata.context = pstrdup(_("parallel worker"));
}
/*
* Context beyond that should use the error context callbacks
* that were in effect when the ParallelContext was created,
* not the current ones.
*/
save_error_context_stack = error_context_stack;
error_context_stack = pcxt->error_context_stack;
/* Rethrow error or print notice. */
ThrowErrorData(&edata);
/* Not an error, so restore previous context stack. */
error_context_stack = save_error_context_stack;
break;
}
case 'A': /* NotifyResponse */
{
/* Propagate NotifyResponse. */
int32 pid;
const char *channel;
const char *payload;
pid = pq_getmsgint(msg, 4);
channel = pq_getmsgrawstring(msg);
payload = pq_getmsgrawstring(msg);
pq_endmessage(msg);
NotifyMyFrontEnd(channel, payload, pid);
break;
}
case 'X': /* Terminate, indicating clean exit */
{
shm_mq_detach(pcxt->worker[i].error_mqh);
pcxt->worker[i].error_mqh = NULL;
break;
}
default:
{
elog(ERROR, "unrecognized message type received from parallel worker: %c (message length %d bytes)",
msgtype, msg->len);
}
}
}
/*
* End-of-subtransaction cleanup for parallel contexts.
*
* Currently, it's forbidden to enter or leave a subtransaction while
* parallel mode is in effect, so we could just blow away everything. But
* we may want to relax that restriction in the future, so this code
* contemplates that there may be multiple subtransaction IDs in pcxt_list.
*/
void
AtEOSubXact_Parallel(bool isCommit, SubTransactionId mySubId)
{
while (!dlist_is_empty(&pcxt_list))
{
ParallelContext *pcxt;
pcxt = dlist_head_element(ParallelContext, node, &pcxt_list);
if (pcxt->subid != mySubId)
break;
if (isCommit)
elog(WARNING, "leaked parallel context");
DestroyParallelContext(pcxt);
}
}
/*
* End-of-transaction cleanup for parallel contexts.
*/
void
AtEOXact_Parallel(bool isCommit)
{
while (!dlist_is_empty(&pcxt_list))
{
ParallelContext *pcxt;
pcxt = dlist_head_element(ParallelContext, node, &pcxt_list);
if (isCommit)
elog(WARNING, "leaked parallel context");
DestroyParallelContext(pcxt);
}
}
/*
* Main entrypoint for parallel workers.
*/
void
ParallelWorkerMain(Datum main_arg)
{
dsm_segment *seg;
shm_toc *toc;
FixedParallelState *fps;
char *error_queue_space;
shm_mq *mq;
shm_mq_handle *mqh;
char *libraryspace;
char *entrypointstate;
char *library_name;
char *function_name;
parallel_worker_main_type entrypt;
char *gucspace;
char *combocidspace;
char *tsnapspace;
char *asnapspace;
char *tstatespace;
char *reindexspace;
char *relmapperspace;
char *enumblacklistspace;
StringInfoData msgbuf;
char *session_dsm_handle_space;
/* Set flag to indicate that we're initializing a parallel worker. */
InitializingParallelWorker = true;
/* Establish signal handlers. */
pqsignal(SIGTERM, die);
BackgroundWorkerUnblockSignals();
/* Determine and set our parallel worker number. */
Assert(ParallelWorkerNumber == -1);
memcpy(&ParallelWorkerNumber, MyBgworkerEntry->bgw_extra, sizeof(int));
/* Set up a memory context to work in, just for cleanliness. */
CurrentMemoryContext = AllocSetContextCreate(TopMemoryContext,
"Parallel worker",
ALLOCSET_DEFAULT_SIZES);
/*
* Attach to the dynamic shared memory segment for the parallel query, and
* find its table of contents.
*
* Note: at this point, we have not created any ResourceOwner in this
* process. This will result in our DSM mapping surviving until process
* exit, which is fine. If there were a ResourceOwner, it would acquire
* ownership of the mapping, but we have no need for that.
*/
seg = dsm_attach(DatumGetUInt32(main_arg));
if (seg == NULL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not map dynamic shared memory segment")));
toc = shm_toc_attach(PARALLEL_MAGIC, dsm_segment_address(seg));
if (toc == NULL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("invalid magic number in dynamic shared memory segment")));
/* Look up fixed parallel state. */
fps = shm_toc_lookup(toc, PARALLEL_KEY_FIXED, false);
MyFixedParallelState = fps;
/* Arrange to signal the leader if we exit. */
ParallelMasterPid = fps->parallel_master_pid;
ParallelMasterBackendId = fps->parallel_master_backend_id;
on_shmem_exit(ParallelWorkerShutdown, (Datum) 0);
/*
* Now we can find and attach to the error queue provided for us. That's
* good, because until we do that, any errors that happen here will not be
* reported back to the process that requested that this worker be
* launched.
*/
error_queue_space = shm_toc_lookup(toc, PARALLEL_KEY_ERROR_QUEUE, false);
mq = (shm_mq *) (error_queue_space +
ParallelWorkerNumber * PARALLEL_ERROR_QUEUE_SIZE);
shm_mq_set_sender(mq, MyProc);
mqh = shm_mq_attach(mq, seg, NULL);
pq_redirect_to_shm_mq(seg, mqh);
pq_set_parallel_master(fps->parallel_master_pid,
fps->parallel_master_backend_id);
/*
* Send a BackendKeyData message to the process that initiated parallelism
* so that it has access to our PID before it receives any other messages
* from us. Our cancel key is sent, too, since that's the way the
* protocol message is defined, but it won't actually be used for anything
* in this case.
*/
pq_beginmessage(&msgbuf, 'K');
pq_sendint32(&msgbuf, (int32) MyProcPid);
pq_sendint32(&msgbuf, (int32) MyCancelKey);
pq_endmessage(&msgbuf);
/*
* Hooray! Primary initialization is complete. Now, we need to set up our
* backend-local state to match the original backend.
*/
/*
* Join locking group. We must do this before anything that could try to
* acquire a heavyweight lock, because any heavyweight locks acquired to
* this point could block either directly against the parallel group
* leader or against some process which in turn waits for a lock that
* conflicts with the parallel group leader, causing an undetected
* deadlock. (If we can't join the lock group, the leader has gone away,
* so just exit quietly.)
*/
if (!BecomeLockGroupMember(fps->parallel_master_pgproc,
fps->parallel_master_pid))
return;
/*
* Restore transaction and statement start-time timestamps. This must
* happen before anything that would start a transaction, else asserts in
* xact.c will fire.
*/
SetParallelStartTimestamps(fps->xact_ts, fps->stmt_ts);
/*
* Identify the entry point to be called. In theory this could result in
* loading an additional library, though most likely the entry point is in
* the core backend or in a library we just loaded.
*/
entrypointstate = shm_toc_lookup(toc, PARALLEL_KEY_ENTRYPOINT, false);
library_name = entrypointstate;
function_name = entrypointstate + strlen(library_name) + 1;
entrypt = LookupParallelWorkerFunction(library_name, function_name);
/* Restore database connection. */
BackgroundWorkerInitializeConnectionByOid(fps->database_id,
fps->authenticated_user_id,
0);
/*
* Set the client encoding to the database encoding, since that is what
* the leader will expect.
*/
SetClientEncoding(GetDatabaseEncoding());
/*
* Load libraries that were loaded by original backend. We want to do
* this before restoring GUCs, because the libraries might define custom
* variables.
*/
libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false);
StartTransactionCommand();
RestoreLibraryState(libraryspace);
/* Restore GUC values from launching backend. */
gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
RestoreGUCState(gucspace);
CommitTransactionCommand();
/* Crank up a transaction state appropriate to a parallel worker. */
tstatespace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_STATE, false);
StartParallelWorkerTransaction(tstatespace);
/* Restore combo CID state. */
combocidspace = shm_toc_lookup(toc, PARALLEL_KEY_COMBO_CID, false);
RestoreComboCIDState(combocidspace);
/* Attach to the per-session DSM segment and contained objects. */
session_dsm_handle_space =
shm_toc_lookup(toc, PARALLEL_KEY_SESSION_DSM, false);
AttachSession(*(dsm_handle *) session_dsm_handle_space);
/* Restore transaction snapshot. */
tsnapspace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_SNAPSHOT, false);
RestoreTransactionSnapshot(RestoreSnapshot(tsnapspace),
fps->parallel_master_pgproc);
/* Restore active snapshot. */
asnapspace = shm_toc_lookup(toc, PARALLEL_KEY_ACTIVE_SNAPSHOT, false);
PushActiveSnapshot(RestoreSnapshot(asnapspace));
/*
* We've changed which tuples we can see, and must therefore invalidate
* system caches.
*/
InvalidateSystemCaches();
/*
* Restore current role id. Skip verifying whether session user is
* allowed to become this role and blindly restore the leader's state for
* current role.
*/
SetCurrentRoleId(fps->outer_user_id, fps->is_superuser);
/* Restore user ID and security context. */
SetUserIdAndSecContext(fps->current_user_id, fps->sec_context);
/* Restore temp-namespace state to ensure search path matches leader's. */
SetTempNamespaceState(fps->temp_namespace_id,
fps->temp_toast_namespace_id);
/* Restore reindex state. */
reindexspace = shm_toc_lookup(toc, PARALLEL_KEY_REINDEX_STATE, false);
RestoreReindexState(reindexspace);
/* Restore relmapper state. */
relmapperspace = shm_toc_lookup(toc, PARALLEL_KEY_RELMAPPER_STATE, false);
RestoreRelationMap(relmapperspace);
/* Restore enum blacklist. */
enumblacklistspace = shm_toc_lookup(toc, PARALLEL_KEY_ENUMBLACKLIST,
false);
RestoreEnumBlacklist(enumblacklistspace);
/* Attach to the leader's serializable transaction, if SERIALIZABLE. */
AttachSerializableXact(fps->serializable_xact_handle);
/*
* We've initialized all of our state now; nothing should change
* hereafter.
*/
InitializingParallelWorker = false;
EnterParallelMode();
/*
* Time to do the real work: invoke the caller-supplied code.
*/
entrypt(seg, toc);
/* Must exit parallel mode to pop active snapshot. */
ExitParallelMode();
/* Must pop active snapshot so snapmgr.c doesn't complain. */
PopActiveSnapshot();
/* Shut down the parallel-worker transaction. */
EndParallelWorkerTransaction();
/* Detach from the per-session DSM segment. */
DetachSession();
/* Report success. */
pq_putmessage('X', NULL, 0);
}
/*
* Update shared memory with the ending location of the last WAL record we
* wrote, if it's greater than the value already stored there.
*/
void
ParallelWorkerReportLastRecEnd(XLogRecPtr last_xlog_end)
{
FixedParallelState *fps = MyFixedParallelState;
Assert(fps != NULL);
SpinLockAcquire(&fps->mutex);
if (fps->last_xlog_end < last_xlog_end)
fps->last_xlog_end = last_xlog_end;
SpinLockRelease(&fps->mutex);
}
/*
* Make sure the leader tries to read from our error queue one more time.
* This guards against the case where we exit uncleanly without sending an
* ErrorResponse to the leader, for example because some code calls proc_exit
* directly.
*/
static void
ParallelWorkerShutdown(int code, Datum arg)
{
SendProcSignal(ParallelMasterPid,
PROCSIG_PARALLEL_MESSAGE,
ParallelMasterBackendId);
}
/*
* Look up (and possibly load) a parallel worker entry point function.
*
* For functions contained in the core code, we use library name "postgres"
* and consult the InternalParallelWorkers array. External functions are
* looked up, and loaded if necessary, using load_external_function().
*
* The point of this is to pass function names as strings across process
* boundaries. We can't pass actual function addresses because of the
* possibility that the function has been loaded at a different address
* in a different process. This is obviously a hazard for functions in
* loadable libraries, but it can happen even for functions in the core code
* on platforms using EXEC_BACKEND (e.g., Windows).
*
* At some point it might be worthwhile to get rid of InternalParallelWorkers[]
* in favor of applying load_external_function() for core functions too;
* but that raises portability issues that are not worth addressing now.
*/
static parallel_worker_main_type
LookupParallelWorkerFunction(const char *libraryname, const char *funcname)
{
/*
* If the function is to be loaded from postgres itself, search the
* InternalParallelWorkers array.
*/
if (strcmp(libraryname, "postgres") == 0)
{
int i;
for (i = 0; i < lengthof(InternalParallelWorkers); i++)
{
if (strcmp(InternalParallelWorkers[i].fn_name, funcname) == 0)
return InternalParallelWorkers[i].fn_addr;
}
/* We can only reach this by programming error. */
elog(ERROR, "internal function \"%s\" not found", funcname);
}
/* Otherwise load from external library. */
return (parallel_worker_main_type)
load_external_function(libraryname, funcname, true, NULL);
}
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