Expand LogEntry method docs.

In particular:
* point to LOG mutator methods that can affect their values
* point out lifetime hazards with ABSL_ATTRIBUTE_LIFETIME_BOUND

PiperOrigin-RevId: 477725823
Change-Id: I38cb434b300ceea3cceb2c42eb406bba8e1049d4
pull/1283/head
Andy Getzendanner 3 years ago committed by Copybara-Service
parent dce028bdce
commit f8b5a041bd
  1. 1
      absl/log/BUILD.bazel
  2. 1
      absl/log/CMakeLists.txt
  3. 101
      absl/log/log_entry.h

@ -128,6 +128,7 @@ cc_library(
linkopts = ABSL_DEFAULT_LINKOPTS,
deps = [
"//absl/base:config",
"//absl/base:core_headers",
"//absl/base:log_severity",
"//absl/log/internal:config",
"//absl/strings",

@ -450,6 +450,7 @@ absl_cc_library(
${ABSL_DEFAULT_LINKOPTS}
DEPS
absl::config
absl::core_headers
absl::log_internal_config
absl::log_severity
absl::span

@ -27,6 +27,7 @@
#include <cstddef>
#include <string>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/log_severity.h"
#include "absl/log/internal/config.h"
@ -45,9 +46,10 @@ class LogMessage;
// LogEntry
//
// Represents a single entry in a log, i.e., one log message.
// Represents a single entry in a log, i.e., one `LOG` statement or failed
// `CHECK`.
//
// LogEntry is copyable and thread-compatible.
// `LogEntry` is copyable and thread-compatible.
class LogEntry final {
public:
using tid_t = log_internal::Tid;
@ -59,84 +61,127 @@ class LogEntry final {
LogEntry(const LogEntry&) = default;
LogEntry& operator=(const LogEntry&) = default;
// Source file and line where the log message occurred.
// Take special care not to dereference the pointers returned by
// source_filename() and source_basename() after the lifetime of the
// `LogEntry`. This will usually work, because these are usually backed by a
// statically allocated char array obtained from the `__FILE__` macro, but
// it is nevertheless incorrect and will be broken by statements like
// `LOG(INFO).AtLocation(...)` (see above). If you need the data later, you
// must copy it.
absl::string_view source_filename() const { return full_filename_; }
absl::string_view source_basename() const { return base_filename_; }
// Source file and line where the log message occurred. Taken from `__FILE__`
// and `__LINE__` unless overridden by `LOG(...).AtLocation(...)`.
//
// Take special care not to use the values returned by `source_filename()` and
// `source_basename()` after the lifetime of the entry. This is always
// incorrect, but it will often work in practice because they usually point
// into a statically allocated character array obtained from `__FILE__`.
// Statements like `LOG(INFO).AtLocation(std::string(...), ...)` will expose
// the bug. If you need the data later, you must copy them.
absl::string_view source_filename() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return full_filename_;
}
absl::string_view source_basename() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return base_filename_;
}
int source_line() const { return line_; }
// LogEntry::prefix()
//
// True unless cleared by LOG(...).NoPrefix(), which indicates suppression of
// the line prefix containing metadata like file, line, timestamp, etc.
// True unless the metadata prefix was suppressed once by
// `LOG(...).NoPrefix()` or globally by `absl::EnableLogPrefix(false)`.
// Implies `text_message_with_prefix() == text_message()`.
bool prefix() const { return prefix_; }
// LogEntry::log_severity()
//
// Returns this LogEntry's severity.
// Returns this entry's severity. For `LOG`, taken from the first argument;
// for `CHECK`, always `absl::LogSeverity::kFatal`.
absl::LogSeverity log_severity() const { return severity_; }
// LogEntry::verbosity()
//
// Returns this LogEntry's verbosity, or kNoVerbosityLevel for a non-verbose
// LogEntry.
// Returns this entry's verbosity, or `kNoVerbosityLevel` for a non-verbose
// entry. Verbosity control is not available outside of Google yet.
int verbosity() const { return verbose_level_; }
// LogEntry::timestamp()
//
// Returns the time at which this LogEntry was written.
// Returns the time at which this entry was written. Captured during
// evaluation of `LOG`, but can be overridden by
// `LOG(...).WithTimestamp(...)`.
//
// Take care not to rely on timestamps increasing monotonically, or even to
// rely on timestamps having any particular relationship with reality (since
// they can be overridden).
absl::Time timestamp() const { return timestamp_; }
// LogEntry::tid()
//
// Returns the id of the thread that wrote this LogEntry.
// Returns the ID of the thread that wrote this entry. Captured during
// evaluation of `LOG`, but can be overridden by `LOG(...).WithThreadID(...)`.
//
// Take care not to *rely* on reported thread IDs as they can be overridden as
// specified above.
tid_t tid() const { return tid_; }
// Text-formatted version of the log message. An underlying buffer holds:
// Text-formatted version of the log message. An underlying buffer holds
// these contiguous data:
//
// * A prefix formed by formatting metadata (timestamp, filename, line number,
// etc.)
// The prefix may be empty - see `LogEntry::prefix()` - and may rarely be
// truncated if the metadata are very long.
// * The streamed data
// The data may be empty if nothing was streamed, or may be truncated to fit
// the buffer.
// * A newline
// * A nul terminator
//
// These methods give access to the most commonly-used substrings of the
// The newline and nul terminator will be present even if the prefix and/or
// data are truncated.
//
// These methods give access to the most commonly useful substrings of the
// buffer's contents. Other combinations can be obtained with substring
// arithmetic.
absl::string_view text_message_with_prefix_and_newline() const {
//
// The buffer does not outlive the entry; if you need the data later, you must
// copy them.
absl::string_view text_message_with_prefix_and_newline() const
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return absl::string_view(
text_message_with_prefix_and_newline_and_nul_.data(),
text_message_with_prefix_and_newline_and_nul_.size() - 1);
}
absl::string_view text_message_with_prefix() const {
absl::string_view text_message_with_prefix() const
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return absl::string_view(
text_message_with_prefix_and_newline_and_nul_.data(),
text_message_with_prefix_and_newline_and_nul_.size() - 2);
}
absl::string_view text_message_with_newline() const {
absl::string_view text_message_with_newline() const
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return absl::string_view(
text_message_with_prefix_and_newline_and_nul_.data() + prefix_len_,
text_message_with_prefix_and_newline_and_nul_.size() - prefix_len_ - 1);
}
absl::string_view text_message() const {
absl::string_view text_message() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return absl::string_view(
text_message_with_prefix_and_newline_and_nul_.data() + prefix_len_,
text_message_with_prefix_and_newline_and_nul_.size() - prefix_len_ - 2);
}
const char* text_message_with_prefix_and_newline_c_str() const {
const char* text_message_with_prefix_and_newline_c_str() const
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return text_message_with_prefix_and_newline_and_nul_.data();
}
// LogEntry::stacktrace()
//
// Optional stacktrace, e.g., for `FATAL` logs.
absl::string_view stacktrace() const { return stacktrace_; }
// Optional stacktrace, e.g. for `FATAL` logs and failed `CHECK`s.
//
// Fatal entries are dispatched to each sink twice: first with all data and
// metadata but no stacktrace, and then with the stacktrace. This is done
// because stacktrace collection is sometimes slow and fallible, and it's
// critical to log enough information to diagnose the failure even if the
// stacktrace collection hangs.
//
// The buffer does not outlive the entry; if you need the data later, you must
// copy them.
absl::string_view stacktrace() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return stacktrace_;
}
private:
LogEntry() = default;

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