jit.c

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/*-------------------------------------------------------------------------
 *
 * jit.c
 *    Provider independent JIT infrastructure.
 *
 * Code related to loading JIT providers, redirecting calls into JIT providers
 * and error handling.  No code specific to a specific JIT implementation
 * should end up here.
 *
 *
 * Copyright (c) 2016-2023, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/jit/jit.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
 
#include "executor/execExpr.h"
#include "fmgr.h"
#include "jit/jit.h"
#include "miscadmin.h"
#include "utils/fmgrprotos.h"
#include "utils/resowner_private.h"
 
/* GUCs */
bool        jit_enabled = true;
char       *jit_provider = NULL;
bool        jit_debugging_support = false;
bool        jit_dump_bitcode = false;
bool        jit_expressions = true;
bool        jit_profiling_support = false;
bool        jit_tuple_deforming = true;
double      jit_above_cost = 100000;
double      jit_inline_above_cost = 500000;
double      jit_optimize_above_cost = 500000;
 
static JitProviderCallbacks provider;
static bool provider_successfully_loaded = false;
static bool provider_failed_loading = false;
 
 
static bool provider_init(void);
static bool file_exists(const char *name);
 
 
/*
 * SQL level function returning whether JIT is available in the current
 * backend. Will attempt to load JIT provider if necessary.
 */
Datum
pg_jit_available(PG_FUNCTION_ARGS)
{
    PG_RETURN_BOOL(provider_init());
}
 
 
/*
 * Return whether a JIT provider has successfully been loaded, caching the
 * result.
 */
static bool
provider_init(void)
{
    char        path[MAXPGPATH];
    JitProviderInit init;
 
    /* don't even try to load if not enabled */
    if (!jit_enabled)
        return false;
 
    /*
     * Don't retry loading after failing - attempting to load JIT provider
     * isn't cheap.
     */
    if (provider_failed_loading)
        return false;
    if (provider_successfully_loaded)
        return true;
 
    /*
     * Check whether shared library exists. We do that check before actually
     * attempting to load the shared library (via load_external_function()),
     * because that'd error out in case the shlib isn't available.
     */
    snprintf(path, MAXPGPATH, "%s/%s%s", pkglib_path, jit_provider, DLSUFFIX);
    elog(DEBUG1, "probing availability of JIT provider at %s", path);
    if (!file_exists(path))
    {
        elog(DEBUG1,
             "provider not available, disabling JIT for current session");
        provider_failed_loading = true;
        return false;
    }
 
    /*
     * If loading functions fails, signal failure. We do so because
     * load_external_function() might error out despite the above check if
     * e.g. the library's dependencies aren't installed. We want to signal
     * ERROR in that case, so the user is notified, but we don't want to
     * continually retry.
     */
    provider_failed_loading = true;
 
    /* and initialize */
    init = (JitProviderInit)
        load_external_function(path, "_PG_jit_provider_init", true, NULL);
    init(&provider);
 
    provider_successfully_loaded = true;
    provider_failed_loading = false;
 
    elog(DEBUG1, "successfully loaded JIT provider in current session");
 
    return true;
}
 
/*
 * Reset JIT provider's error handling. This'll be called after an error has
 * been thrown and the main-loop has re-established control.
 */
void
jit_reset_after_error(void)
{
    if (provider_successfully_loaded)
        provider.reset_after_error();
}
 
/*
 * Release resources required by one JIT context.
 */
void
jit_release_context(JitContext *context)
{
    if (provider_successfully_loaded)
        provider.release_context(context);
 
    ResourceOwnerForgetJIT(context->resowner, PointerGetDatum(context));
    pfree(context);
}
 
/*
 * Ask provider to JIT compile an expression.
 *
 * Returns true if successful, false if not.
 */
bool
jit_compile_expr(struct ExprState *state)
{
    /*
     * We can easily create a one-off context for functions without an
     * associated PlanState (and thus EState). But because there's no executor
     * shutdown callback that could deallocate the created function, they'd
     * live to the end of the transactions, where they'd be cleaned up by the
     * resowner machinery. That can lead to a noticeable amount of memory
     * usage, and worse, trigger some quadratic behaviour in gdb. Therefore,
     * at least for now, don't create a JITed function in those circumstances.
     */
    if (!state->parent)
        return false;
 
    /* if no jitting should be performed at all */
    if (!(state->parent->state->es_jit_flags & PGJIT_PERFORM))
        return false;
 
    /* or if expressions aren't JITed */
    if (!(state->parent->state->es_jit_flags & PGJIT_EXPR))
        return false;
 
    /* this also takes !jit_enabled into account */
    if (provider_init())
        return provider.compile_expr(state);
 
    return false;
}
 
/* Aggregate JIT instrumentation information */
void
InstrJitAgg(JitInstrumentation *dst, JitInstrumentation *add)
{
    dst->created_functions += add->created_functions;
    INSTR_TIME_ADD(dst->generation_counter, add->generation_counter);
    INSTR_TIME_ADD(dst->inlining_counter, add->inlining_counter);
    INSTR_TIME_ADD(dst->optimization_counter, add->optimization_counter);
    INSTR_TIME_ADD(dst->emission_counter, add->emission_counter);
}
 
static bool
file_exists(const char *name)
{
    struct stat st;
 
    Assert(name != NULL);
 
    if (stat(name, &st) == 0)
        return !S_ISDIR(st.st_mode);
    else if (!(errno == ENOENT || errno == ENOTDIR))
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not access file \"%s\": %m", name)));
 
    return false;
}