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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef jit_StructuredSpewer_h
#define jit_StructuredSpewer_h
# include "mozilla/Atomics.h"
# include "mozilla/Attributes.h"
# include "mozilla/EnumeratedArray.h"
# include "mozilla/EnumSet.h"
# include "mozilla/Maybe.h"
# include "mozilla/Sprintf.h"
# include "jstypes.h"
# include "vm/JSONPrinter.h"
# include "vm/Printer.h"
# ifdef XP_WIN
# include <process.h>
# define getpid _getpid
# else
# include <unistd.h>
# endif
// [SMDOC] JSON Structured Spewer
// This spewer design has two goals:
// 1. Provide a spew mechanism that has first-class support for slicing and
// dicing output. This means that filtering by script and channel should be
// the dominant output mechanism.
// 2. Provide a simple powerful mechanism for getting information out of the
// compiler and into tools. I'm inspired by tools like CacheIR analyzer,
// IR Hydra, and the upcoming tracelogger integration into
// The spewer has four main control knobs, all currently set as
// environment variables. All but the first are optional. When the spewer is
// activated through the browser, it is synchronized with the gecko profiler
// start and stop routines. Setting SPEW=AtStartup activates the spewer at
// startup instead of profiler start, but profiler stop will still deactivate
// the spewer.
// SPEW: Activates the spewer. The value provided is interpreted as a comma
// separated list that selects channels by name. Currently there's no
// mapping between internal and external names, so the channel names
// are exactly those described in STRUCTURED_CHANNEL_LIST below.
// SPEW_FILE: Selects the file to write to. An absolute path.
// SPEW_FILTER: A string which is matched against 'signature' constructed or a
// JSScript, currently connsisting of filename:line:col.
// Matching in this version is merely finding the string in
// in question in the 'signature'
// SPEW_UPLOAD: If this variable is set as well as MOZ_UPLOAD_DIR, output goes
// to $MOZ_UPLOAD_DIR/spew_output* to ease usage with Treeherder.
// Other notes:
// - Thread safety is provided by opening a new spewer file for every thread.
// - Each file is prefixed with the PID to handle multiple processes.
// - Files are opened lazily, just before the first write to them.
class JS_PUBLIC_API JSScript;
namespace js {
_(BaselineICStats) \
_(ScriptStats) \
// Structured spew channels
enum class SpewChannel {
# define STRUCTURED_CHANNEL(name) name,
// A filter is used to select what channel is enabled
// To save memory, JSScripts do not have their own filters, but instead have
// a single bit which tracks if that script has opted into spewing.
class StructuredSpewFilter {
// Indicates what spew channel is enabled.
SpewChannel channel_ = SpewChannel::Disabled;
// Return true iff any channel is enabled.
bool isChannelSelected() const {
return !(channel_ == SpewChannel::Disabled);
// Return true iff spew is enabled for this channel for
// the script this was created for.
bool enabled(SpewChannel x) const { return channel_ == x; }
// Returns true if we have enabled a new channel, false otherwise.
bool enableChannel(SpewChannel x) {
// Assert that we are not going to set the channel to
// SpewChannel::Disabled.
MOZ_ASSERT(x != SpewChannel::Disabled);
if (!isChannelSelected()) {
channel_ = x;
return true;
return false;
void disableAllChannels() { channel_ = SpewChannel::Disabled; }
class StructuredSpewer {
: outputInitializationAttempted_(false),
selectedChannel_() {
if (getenv("SPEW")) {
~StructuredSpewer() {
if (json_.isSome()) {
void enableSpewing() { spewingEnabled_++; }
void disableSpewing() {
MOZ_ASSERT(spewingEnabled_ > 0);
// Check if the spewer is enabled for a particular script, used to power
// script level filtering.
bool enabled(JSScript* script);
// A generic printf like spewer that logs the formatted string.
static void spew(JSContext* cx, SpewChannel channel, const char* fmt, ...)
// Returns true iff the channel is enabled for the given script.
bool enabled(JSContext* cx, const JSScript* script,
SpewChannel channel) const;
// In order to support lazy initialization, and simultaneously support a
// failure to open a log file being non-fatal (as lazily reporting failure
// would be hard, we have an akward set of states to represent.
// We need to handle:
// - Output file not initialized, and not yet attempted
// - Output file not intialized, attempted, and failed.
// - Output file initialized, JSON writer ready for input.
// Because Fprinter doesn't record whether or not its initialization was
// attempted, we keep track of that here.
// The contract we require is that ensureInitializationAttempted() be called
// just before any attempte to write. This will ensure the file open is
// attemped in the right place.
bool outputInitializationAttempted_;
// Indicates the number of times spewing has been enabled. If
// spewingEnabled_ is greater than zero, then spewing is enabled.
size_t spewingEnabled_;
Fprinter output_;
mozilla::Maybe<JSONPrinter> json_;
// Globally selected channel.
StructuredSpewFilter selectedChannel_;
using NameArray =
mozilla::EnumeratedArray<SpewChannel, SpewChannel::Count, const char*>;
// Channel Names
static NameArray const names_;
// Get channel name
static const char* getName(SpewChannel channel) { return names_[channel]; }
// Call just before writes to the output are expected.
// Avoids opening files that will remain empty
// Returns true iff we are able to write now.
bool ensureInitializationAttempted();
void tryToInitializeOutput(const char* path);
// Using flags, choose the enabled channels for this spewer.
void parseSpewFlags(const char* flags);
// Returns true iff the channels is enabled
bool enabled(SpewChannel channel) {
return (spewingEnabled_ > 0 && selectedChannel_.enabled(channel));
// Start a record
void startObject(JSContext* cx, const JSScript* script, SpewChannel channel);
friend class AutoSpewChannel;
friend class AutoStructuredSpewer;
// An RAII class for accessing the structured spewer.
// This class prefixes the spew with channel and location information.
// Before writing with this Spewer, it must be checked: ie.
// {
// AutoSpew x(...);
// if (x) {
// x->property("lalala", y);
// }
// }
// As the selected channel may not be enabled.
// Note: If the lifespan of two AutoSpewers overlap, then the output
// may not be well defined JSON. These spewers should be given as
// short a lifespan as possible.
// As well, this class cannot be copied or assigned to ensure the
// correct number of destructors fire.
class MOZ_RAII AutoStructuredSpewer {
mozilla::Maybe<JSONPrinter*> printer_;
AutoStructuredSpewer(const AutoStructuredSpewer&) = delete;
void operator=(AutoStructuredSpewer&) = delete;
explicit AutoStructuredSpewer(JSContext* cx, SpewChannel channel,
JSScript* script);
~AutoStructuredSpewer() {
if (printer_.isSome()) {
explicit operator bool() const { return printer_.isSome(); }
JSONPrinter* operator->() {
return printer_.ref();
JSONPrinter& operator*() {
return *printer_.ref();
// An RAII class for setting a structured spewer's channel.
// This class is used to set a spewer's channel and then automatically
// unset the channel when AutoSpewChannel goes out of scope.
class MOZ_RAII AutoSpewChannel {
JSContext* cx_;
bool wasChannelAutoSet = false;
AutoSpewChannel(const AutoSpewChannel&) = delete;
void operator=(AutoSpewChannel&) = delete;
explicit AutoSpewChannel(JSContext* cx, SpewChannel channel,
JSScript* script);
} // namespace js
#endif /* jit_StructuredSpewer_h */