Adding upstream version 43.9.upstream/43.9upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 959 insertions, 0 deletions

diff --git a/src/shell-perf-log.c b/src/shell-perf-log.c
new file mode 100644
index 0000000..3bd5228
--- /dev/null
+++ b/src/shell-perf-log.c
@@ -0,0 +1,959 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+#include "config.h"
+
+#include <string.h>
+
+#include "shell-perf-log.h"
+
+typedef struct _ShellPerfEvent ShellPerfEvent;
+typedef struct _ShellPerfStatistic ShellPerfStatistic;
+typedef struct _ShellPerfStatisticsClosure ShellPerfStatisticsClosure;
+typedef union  _ShellPerfStatisticValue ShellPerfStatisticValue;
+typedef struct _ShellPerfBlock ShellPerfBlock;
+
+/**
+ * SECTION:shell-perf-log
+ * @short_description: Event recorder for performance measurement
+ *
+ * ShellPerfLog provides a way for different parts of the code to
+ * record information for subsequent analysis and interactive
+ * exploration. Events exist of a timestamp, an event ID, and
+ * arguments to the event.
+ *
+ * Emphasis is placed on storing recorded events in a compact
+ * fashion so log recording disturbs the execution of the program
+ * as little as possible, however events should not be recorded
+ * at too fine a granularity - an event that is recorded once
+ * per frame or once per user action is appropriate, an event that
+ * occurs many times per frame is not.
+ *
+ * Arguments are identified by a D-Bus style signature; at the moment
+ * only a limited number of event signatures are supported to
+ * simplify the code.
+ */
+struct _ShellPerfLog
+{
+  GObject parent;
+
+  GPtrArray *events;
+  GHashTable *events_by_name;
+  GPtrArray *statistics;
+  GHashTable *statistics_by_name;
+
+  GPtrArray *statistics_closures;
+
+  GQueue *blocks;
+
+  gint64 start_time;
+  gint64 last_time;
+
+  guint statistics_timeout_id;
+
+  guint enabled : 1;
+};
+
+struct _ShellPerfEvent
+{
+  guint16 id;
+  char *name;
+  char *description;
+  char *signature;
+};
+
+union _ShellPerfStatisticValue
+{
+  int i;
+  gint64 x;
+};
+
+struct _ShellPerfStatistic
+{
+  ShellPerfEvent *event;
+
+  ShellPerfStatisticValue current_value;
+  ShellPerfStatisticValue last_value;
+
+  guint initialized : 1;
+  guint recorded : 1;
+};
+
+struct _ShellPerfStatisticsClosure
+{
+  ShellPerfStatisticsCallback callback;
+  gpointer user_data;
+  GDestroyNotify notify;
+};
+
+/* The events in the log are stored in a linked list of fixed size
+ * blocks.
+ *
+ * Note that the power-of-two nature of BLOCK_SIZE here is superficial
+ * since the allocated block has the 'bytes' field and malloc
+ * overhead. The current value is well below the size that will
+ * typically be independently mmapped by the malloc implementation so
+ * it doesn't matter. If we switched to mmapping blocks manually
+ * (perhaps to avoid polluting malloc statistics), we'd want to use a
+ * different value of BLOCK_SIZE.
+ */
+#define BLOCK_SIZE 8192
+
+struct _ShellPerfBlock
+{
+  guint32 bytes;
+  guchar buffer[BLOCK_SIZE];
+};
+
+/* Number of milliseconds between periodic statistics collection when
+ * events are enabled. Statistics collection can also be explicitly
+ * triggered.
+ */
+#define STATISTIC_COLLECTION_INTERVAL_MS 5000
+
+/* Builtin events */
+enum {
+  EVENT_SET_TIME,
+  EVENT_STATISTICS_COLLECTED
+};
+
+G_DEFINE_TYPE(ShellPerfLog, shell_perf_log, G_TYPE_OBJECT);
+
+static gint64
+get_time (void)
+{
+  return g_get_monotonic_time ();
+}
+
+static void
+shell_perf_log_init (ShellPerfLog *perf_log)
+{
+  perf_log->events = g_ptr_array_new ();
+  perf_log->events_by_name = g_hash_table_new (g_str_hash, g_str_equal);
+  perf_log->statistics = g_ptr_array_new ();
+  perf_log->statistics_by_name = g_hash_table_new (g_str_hash, g_str_equal);
+  perf_log->statistics_closures = g_ptr_array_new ();
+  perf_log->blocks = g_queue_new ();
+
+  /* This event is used when timestamp deltas are greater than
+   * fits in a gint32. 0xffffffff microseconds is about 70 minutes, so this
+   * is not going to happen in normal usage. It might happen if performance
+   * logging is enabled some time after starting the shell */
+  shell_perf_log_define_event (perf_log, "perf.setTime", "", "x");
+  g_assert (perf_log->events->len == EVENT_SET_TIME + 1);
+
+  /* The purpose of this event is to allow us to optimize out storing
+   * statistics that haven't changed. We want to mark every time we
+   * collect statistics even if we don't record any individual
+   * statistics so that we can distinguish sudden changes from gradual changes.
+   *
+   * The argument is the number of microseconds that statistics collection
+   * took; we record that since statistics collection could start taking
+   * significant time if we do things like grub around in /proc/
+   */
+  shell_perf_log_define_event (perf_log, "perf.statisticsCollected",
+                               "Finished collecting statistics",
+                               "x");
+  g_assert (perf_log->events->len == EVENT_STATISTICS_COLLECTED + 1);
+
+  perf_log->start_time = perf_log->last_time = get_time();
+}
+
+static void
+shell_perf_log_class_init (ShellPerfLogClass *class)
+{
+}
+
+/**
+ * shell_perf_log_get_default:
+ *
+ * Gets the global singleton performance log. This is initially disabled
+ * and must be explicitly enabled with shell_perf_log_set_enabled().
+ *
+ * Return value: (transfer none): the global singleton performance log
+ */
+ShellPerfLog *
+shell_perf_log_get_default (void)
+{
+  static ShellPerfLog *perf_log;
+
+  if (perf_log == NULL)
+    perf_log = g_object_new (SHELL_TYPE_PERF_LOG, NULL);
+
+  return perf_log;
+}
+
+static gboolean
+statistics_timeout (gpointer data)
+{
+  ShellPerfLog *perf_log = data;
+
+  shell_perf_log_collect_statistics (perf_log);
+
+  return TRUE;
+}
+
+/**
+ * shell_perf_log_set_enabled:
+ * @perf_log: a #ShellPerfLog
+ * @enabled: whether to record events
+ *
+ * Sets whether events are currently being recorded.
+ */
+void
+shell_perf_log_set_enabled (ShellPerfLog *perf_log,
+                            gboolean      enabled)
+{
+  enabled = enabled != FALSE;
+
+  if (enabled != perf_log->enabled)
+    {
+      perf_log->enabled = enabled;
+
+      if (enabled)
+        {
+          perf_log->statistics_timeout_id = g_timeout_add (STATISTIC_COLLECTION_INTERVAL_MS,
+                                                           statistics_timeout,
+                                                           perf_log);
+          g_source_set_name_by_id (perf_log->statistics_timeout_id, "[gnome-shell] statistics_timeout");
+        }
+      else
+        {
+          g_clear_handle_id (&perf_log->statistics_timeout_id, g_source_remove);
+        }
+    }
+}
+
+static ShellPerfEvent *
+define_event (ShellPerfLog *perf_log,
+              const char   *name,
+              const char   *description,
+              const char   *signature)
+{
+  ShellPerfEvent *event;
+
+  if (strcmp (signature, "") != 0 &&
+      strcmp (signature, "s") != 0 &&
+      strcmp (signature, "i") != 0 &&
+      strcmp (signature, "x") != 0)
+    {
+      g_warning ("Only supported event signatures are '', 's', 'i', and 'x'\n");
+      return NULL;
+    }
+
+  if (perf_log->events->len == 65536)
+    {
+      g_warning ("Maximum number of events defined\n");
+      return NULL;
+    }
+
+  /* We could do stricter validation, but this will break our JSON dumps */
+  if (strchr (name, '"') != NULL)
+    {
+      g_warning ("Event names can't include '\"'");
+      return NULL;
+    }
+
+  if (g_hash_table_lookup (perf_log->events_by_name, name) != NULL)
+    {
+      g_warning ("Duplicate event event for '%s'\n", name);
+      return NULL;
+    }
+
+  event = g_new (ShellPerfEvent, 1);
+
+  event->id = perf_log->events->len;
+  event->name = g_strdup (name);
+  event->signature = g_strdup (signature);
+  event->description = g_strdup (description);
+
+  g_ptr_array_add (perf_log->events, event);
+  g_hash_table_insert (perf_log->events_by_name, event->name, event);
+
+  return event;
+}
+
+/**
+ * shell_perf_log_define_event:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the event. This should of the form
+ *   '<namespace>.<specific eventf'>, for example
+ *   'clutter.stagePaintDone'.
+ * @description: human readable description of the event.
+ * @signature: signature defining the arguments that event takes.
+ *   This is a string of type characters, using the same characters
+ *   as D-Bus or GVariant. Only a very limited number of signatures
+ *   are supported: , '', 's', 'i', and 'x'. This mean respectively:
+ *   no arguments, one string, one 32-bit integer, and one 64-bit
+ *   integer.
+ *
+ * Defines a performance event for later recording.
+ */
+void
+shell_perf_log_define_event (ShellPerfLog *perf_log,
+                             const char   *name,
+                             const char   *description,
+                             const char   *signature)
+{
+  define_event (perf_log, name, description, signature);
+}
+
+static ShellPerfEvent *
+lookup_event (ShellPerfLog *perf_log,
+              const char   *name,
+              const char   *signature)
+{
+  ShellPerfEvent *event = g_hash_table_lookup (perf_log->events_by_name, name);
+
+  if (G_UNLIKELY (event == NULL))
+    {
+      g_warning ("Discarding unknown event '%s'\n", name);
+      return NULL;
+    }
+
+  if (G_UNLIKELY (strcmp (event->signature, signature) != 0))
+    {
+      g_warning ("Event '%s'; defined with signature '%s', used with '%s'\n",
+                 name, event->signature, signature);
+      return NULL;
+    }
+
+  return event;
+}
+
+static void
+record_event (ShellPerfLog   *perf_log,
+              gint64          event_time,
+              ShellPerfEvent *event,
+              const guchar   *bytes,
+              size_t          bytes_len)
+{
+  ShellPerfBlock *block;
+  size_t total_bytes;
+  guint32 time_delta;
+  guint32 pos;
+
+  if (!perf_log->enabled)
+    return;
+
+  total_bytes = sizeof (gint32) + sizeof (gint16) + bytes_len;
+  if (G_UNLIKELY (bytes_len > BLOCK_SIZE || total_bytes > BLOCK_SIZE))
+    {
+      g_warning ("Discarding oversize event '%s'\n", event->name);
+      return;
+    }
+
+  if (event_time > perf_log->last_time + G_GINT64_CONSTANT(0xffffffff))
+    {
+      perf_log->last_time = event_time;
+      record_event (perf_log, event_time,
+                    lookup_event (perf_log, "perf.setTime", "x"),
+                    (const guchar *)&event_time, sizeof(gint64));
+      time_delta = 0;
+    }
+  else if (event_time < perf_log->last_time)
+    time_delta = 0;
+  else
+    time_delta = (guint32)(event_time - perf_log->last_time);
+
+  perf_log->last_time = event_time;
+
+  if (perf_log->blocks->tail == NULL ||
+      total_bytes + ((ShellPerfBlock *)perf_log->blocks->tail->data)->bytes > BLOCK_SIZE)
+    {
+      block = g_new (ShellPerfBlock, 1);
+      block->bytes = 0;
+      g_queue_push_tail (perf_log->blocks, block);
+    }
+  else
+    {
+      block = (ShellPerfBlock *)perf_log->blocks->tail->data;
+    }
+
+  pos = block->bytes;
+
+  memcpy (block->buffer + pos, &time_delta, sizeof (guint32));
+  pos += sizeof (guint32);
+  memcpy (block->buffer + pos, &event->id, sizeof (guint16));
+  pos += sizeof (guint16);
+  memcpy (block->buffer + pos, bytes, bytes_len);
+  pos += bytes_len;
+
+  block->bytes = pos;
+}
+
+/**
+ * shell_perf_log_event:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the event
+ *
+ * Records a performance event with no arguments.
+ */
+void
+shell_perf_log_event (ShellPerfLog *perf_log,
+                      const char   *name)
+{
+  ShellPerfEvent *event = lookup_event (perf_log, name, "");
+  if (G_UNLIKELY (event == NULL))
+    return;
+
+  record_event (perf_log, get_time(), event, NULL, 0);
+}
+
+/**
+ * shell_perf_log_event_i:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the event
+ * @arg: the argument
+ *
+ * Records a performance event with one 32-bit integer argument.
+ */
+void
+shell_perf_log_event_i (ShellPerfLog *perf_log,
+                        const char   *name,
+                        gint32        arg)
+{
+  ShellPerfEvent *event = lookup_event (perf_log, name, "i");
+  if (G_UNLIKELY (event == NULL))
+    return;
+
+  record_event (perf_log, get_time(), event,
+                (const guchar *)&arg, sizeof (arg));
+}
+
+/**
+ * shell_perf_log_event_x:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the event
+ * @arg: the argument
+ *
+ * Records a performance event with one 64-bit integer argument.
+ */
+void
+shell_perf_log_event_x (ShellPerfLog *perf_log,
+                        const char   *name,
+                        gint64        arg)
+{
+  ShellPerfEvent *event = lookup_event (perf_log, name, "x");
+  if (G_UNLIKELY (event == NULL))
+    return;
+
+  record_event (perf_log, get_time(), event,
+                (const guchar *)&arg, sizeof (arg));
+}
+
+/**
+ * shell_perf_log_event_s:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the event
+ * @arg: the argument
+ *
+ * Records a performance event with one string argument.
+ */
+void
+shell_perf_log_event_s (ShellPerfLog *perf_log,
+                         const char   *name,
+                         const char   *arg)
+{
+  ShellPerfEvent *event = lookup_event (perf_log, name, "s");
+  if (G_UNLIKELY (event == NULL))
+    return;
+
+  record_event (perf_log, get_time(), event,
+                (const guchar *)arg, strlen (arg) + 1);
+}
+
+/**
+ * shell_perf_log_define_statistic:
+ * @name: name of the statistic and of the corresponding event.
+ *  This should follow the same guidelines as for shell_perf_log_define_event()
+ * @description: human readable description of the statistic.
+ * @signature: The type of the data stored for statistic. Must
+ *  currently be 'i' or 'x'.
+ *
+ * Defines a statistic. A statistic is a numeric value that is stored
+ * by the performance log and recorded periodically or when
+ * shell_perf_log_collect_statistics() is called explicitly.
+ *
+ * Code that defines a statistic should update it by calling
+ * the update function for the particular data type of the statistic,
+ * such as shell_perf_log_update_statistic_i(). This can be done
+ * at any time, but would normally done inside a function registered
+ * with shell_perf_log_add_statistics_callback(). These functions
+ * are called immediately before statistics are recorded.
+ */
+void
+shell_perf_log_define_statistic (ShellPerfLog *perf_log,
+                                 const char   *name,
+                                 const char   *description,
+                                 const char   *signature)
+{
+  ShellPerfEvent *event;
+  ShellPerfStatistic *statistic;
+
+  if (strcmp (signature, "i") != 0 &&
+      strcmp (signature, "x") != 0)
+    {
+      g_warning ("Only supported statistic signatures are 'i' and 'x'\n");
+      return;
+    }
+
+  event = define_event (perf_log, name, description, signature);
+  if (event == NULL)
+    return;
+
+  statistic = g_new (ShellPerfStatistic, 1);
+  statistic->event = event;
+
+  statistic->initialized = FALSE;
+  statistic->recorded = FALSE;
+
+  g_ptr_array_add (perf_log->statistics, statistic);
+  g_hash_table_insert (perf_log->statistics_by_name, event->name, statistic);
+}
+
+static ShellPerfStatistic *
+lookup_statistic (ShellPerfLog *perf_log,
+                  const char   *name,
+                  const char   *signature)
+{
+  ShellPerfStatistic *statistic = g_hash_table_lookup (perf_log->statistics_by_name, name);
+
+  if (G_UNLIKELY (statistic == NULL))
+    {
+      g_warning ("Unknown statistic '%s'\n", name);
+      return NULL;
+    }
+
+  if (G_UNLIKELY (strcmp (statistic->event->signature, signature) != 0))
+    {
+      g_warning ("Statistic '%s'; defined with signature '%s', used with '%s'\n",
+                 name, statistic->event->signature, signature);
+      return NULL;
+    }
+
+  return statistic;
+}
+
+/**
+ * shell_perf_log_update_statistic_i:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the statistic
+ * @value: new value for the statistic
+ *
+ * Updates the current value of an 32-bit integer statistic.
+ */
+void
+shell_perf_log_update_statistic_i (ShellPerfLog *perf_log,
+                                   const char   *name,
+                                   gint32        value)
+{
+  ShellPerfStatistic *statistic;
+
+  statistic = lookup_statistic (perf_log, name, "i");
+  if (G_UNLIKELY (statistic == NULL))
+      return;
+
+  statistic->current_value.i = value;
+  statistic->initialized = TRUE;
+}
+
+/**
+ * shell_perf_log_update_statistic_x:
+ * @perf_log: a #ShellPerfLog
+ * @name: name of the statistic
+ * @value: new value for the statistic
+ *
+ * Updates the current value of an 64-bit integer statistic.
+ */
+void
+shell_perf_log_update_statistic_x (ShellPerfLog *perf_log,
+                                   const char   *name,
+                                   gint64        value)
+{
+  ShellPerfStatistic *statistic;
+
+  statistic = lookup_statistic (perf_log, name, "x");
+  if (G_UNLIKELY (statistic == NULL))
+      return;
+
+  statistic->current_value.x = value;
+  statistic->initialized = TRUE;
+}
+
+/**
+ * shell_perf_log_add_statistics_callback:
+ * @perf_log: a #ShellPerfLog
+ * @callback: function to call before recording statistics
+ * @user_data: data to pass to @callback
+ * @notify: function to call when @user_data is no longer needed
+ *
+ * Adds a function that will be called before statistics are recorded.
+ * The function would typically compute one or more statistics values
+ * and call a function such as shell_perf_log_update_statistic_i()
+ * to update the value that will be recorded.
+ */
+void
+shell_perf_log_add_statistics_callback (ShellPerfLog               *perf_log,
+                                        ShellPerfStatisticsCallback callback,
+                                        gpointer                    user_data,
+                                        GDestroyNotify              notify)
+{
+  ShellPerfStatisticsClosure *closure = g_new (ShellPerfStatisticsClosure, 1);
+
+  closure->callback = callback;
+  closure->user_data = user_data;
+  closure->notify = notify;
+
+  g_ptr_array_add (perf_log->statistics_closures, closure);
+}
+
+/**
+ * shell_perf_log_collect_statistics:
+ * @perf_log: a #ShellPerfLog
+ *
+ * Calls all the update functions added with
+ * shell_perf_log_add_statistics_callback() and then records events
+ * for all statistics, followed by a perf.statisticsCollected event.
+ */
+void
+shell_perf_log_collect_statistics (ShellPerfLog *perf_log)
+{
+  gint64 event_time = get_time ();
+  gint64 collection_time;
+  guint i;
+
+  if (!perf_log->enabled)
+    return;
+
+  for (i = 0; i < perf_log->statistics_closures->len; i++)
+    {
+      ShellPerfStatisticsClosure *closure;
+
+      closure = g_ptr_array_index (perf_log->statistics_closures, i);
+      closure->callback (perf_log, closure->user_data);
+    }
+
+  collection_time = get_time() - event_time;
+
+  for (i = 0; i < perf_log->statistics->len; i++)
+    {
+      ShellPerfStatistic *statistic = g_ptr_array_index (perf_log->statistics, i);
+
+      if (!statistic->initialized)
+        continue;
+
+      switch (statistic->event->signature[0])
+        {
+        case 'i':
+          if (!statistic->recorded ||
+              statistic->current_value.i != statistic->last_value.i)
+            {
+              record_event (perf_log, event_time, statistic->event,
+                            (const guchar *)&statistic->current_value.i,
+                            sizeof (gint32));
+              statistic->last_value.i = statistic->current_value.i;
+              statistic->recorded = TRUE;
+            }
+          break;
+        case 'x':
+          if (!statistic->recorded ||
+              statistic->current_value.x != statistic->last_value.x)
+            {
+              record_event (perf_log, event_time, statistic->event,
+                            (const guchar *)&statistic->current_value.x,
+                            sizeof (gint64));
+              statistic->last_value.x = statistic->current_value.x;
+              statistic->recorded = TRUE;
+            }
+          break;
+        default:
+          g_warning ("Unsupported signature in event");
+          break;
+        }
+    }
+
+  record_event (perf_log, event_time,
+                g_ptr_array_index (perf_log->events, EVENT_STATISTICS_COLLECTED),
+                (const guchar *)&collection_time, sizeof (gint64));
+}
+
+/**
+ * shell_perf_log_replay:
+ * @perf_log: a #ShellPerfLog
+ * @replay_function: (scope call): function to call for each event in the log
+ * @user_data: data to pass to @replay_function
+ *
+ * Replays the log by calling the given function for each event
+ * in the log.
+ */
+void
+shell_perf_log_replay (ShellPerfLog            *perf_log,
+                       ShellPerfReplayFunction  replay_function,
+                       gpointer                 user_data)
+{
+  gint64 event_time = perf_log->start_time;
+  GList *iter;
+
+  for (iter = perf_log->blocks->head; iter; iter = iter->next)
+    {
+      ShellPerfBlock *block = iter->data;
+      guint32 pos = 0;
+
+      while (pos < block->bytes)
+        {
+          ShellPerfEvent *event;
+          guint16 id;
+          guint32 time_delta;
+          GValue arg = { 0, };
+
+          memcpy (&time_delta, block->buffer + pos, sizeof (guint32));
+          pos += sizeof (guint32);
+          memcpy (&id, block->buffer + pos, sizeof (guint16));
+          pos += sizeof (guint16);
+
+          if (id == EVENT_SET_TIME)
+            {
+              /* Internal, we don't include in the replay */
+              memcpy (&event_time, block->buffer + pos, sizeof (gint64));
+              pos += sizeof (gint64);
+              continue;
+            }
+          else
+            {
+              event_time += time_delta;
+            }
+
+          event = g_ptr_array_index (perf_log->events, id);
+
+          if (strcmp (event->signature, "") == 0)
+            {
+              /* We need to pass something, so pass an empty string */
+              g_value_init (&arg, G_TYPE_STRING);
+            }
+          else if (strcmp (event->signature, "i") == 0)
+            {
+              gint32 l;
+
+              memcpy (&l, block->buffer + pos, sizeof (gint32));
+              pos += sizeof (gint32);
+
+              g_value_init (&arg, G_TYPE_INT);
+              g_value_set_int (&arg, l);
+            }
+          else if (strcmp (event->signature, "x") == 0)
+            {
+              gint64 l;
+
+              memcpy (&l, block->buffer + pos, sizeof (gint64));
+              pos += sizeof (gint64);
+
+              g_value_init (&arg, G_TYPE_INT64);
+              g_value_set_int64 (&arg, l);
+            }
+          else if (strcmp (event->signature, "s") == 0)
+            {
+              g_value_init (&arg, G_TYPE_STRING);
+              g_value_set_string (&arg, (char *)block->buffer + pos);
+              pos += strlen ((char *)(block->buffer + pos)) + 1;
+            }
+
+          replay_function (event_time, event->name, event->signature, &arg, user_data);
+          g_value_unset (&arg);
+        }
+    }
+}
+
+static char *
+escape_quotes (const char *input)
+{
+  GString *result;
+  const char *p;
+
+  if (strchr (input, '"') == NULL)
+    return (char *)input;
+
+  result = g_string_new (NULL);
+  for (p = input; *p; p++)
+    {
+      if (*p == '"')
+        g_string_append (result, "\\\"");
+      else
+        g_string_append_c (result, *p);
+    }
+
+  return g_string_free (result, FALSE);
+}
+
+static gboolean
+write_string (GOutputStream *out,
+              const char    *str,
+              GError       **error)
+{
+  return g_output_stream_write_all (out, str, strlen (str),
+                                    NULL, NULL,
+                                    error);
+}
+
+/**
+ * shell_perf_log_dump_events:
+ * @perf_log: a #ShellPerfLog
+ * @out: output stream into which to write the event definitions
+ * @error: location to store #GError, or %NULL
+ *
+ * Dump the definition of currently defined events and statistics, formatted
+ * as JSON, to the specified output stream. The JSON output is an array,
+ * with each element being a dictionary of the form:
+ *
+ * { name: <name of event>,
+ *   description: <description of string,
+ *   statistic: true } (only for statistics)
+ *
+ * Return value: %TRUE if the dump succeeded. %FALSE if an IO error occurred
+ */
+gboolean
+shell_perf_log_dump_events (ShellPerfLog   *perf_log,
+                            GOutputStream  *out,
+                            GError        **error)
+{
+  GString *output;
+  guint i;
+
+  output = g_string_new (NULL);
+  g_string_append (output, "[ ");
+
+  for (i = 0; i < perf_log->events->len; i++)
+    {
+      ShellPerfEvent *event = g_ptr_array_index (perf_log->events, i);
+      char *escaped_description = escape_quotes (event->description);
+      gboolean is_statistic = g_hash_table_lookup (perf_log->statistics_by_name, event->name) != NULL;
+
+      if (i != 0)
+        g_string_append (output, ",\n  ");
+
+      g_string_append_printf (output,
+                                "{ \"name\": \"%s\",\n"
+                              "    \"description\": \"%s\"",
+                              event->name, escaped_description);
+      if (is_statistic)
+        g_string_append (output, ",\n    \"statistic\": true");
+
+      g_string_append (output, " }");
+
+      if (escaped_description != event->description)
+        g_free (escaped_description);
+    }
+
+  g_string_append (output, " ]");
+
+  return write_string (out, g_string_free (output, FALSE), error);
+}
+
+typedef struct {
+  GOutputStream *out;
+  GError *error;
+  gboolean first;
+} ReplayToJsonClosure;
+
+static void
+replay_to_json (gint64      time,
+                const char *name,
+                const char *signature,
+                GValue     *arg,
+                gpointer    user_data)
+{
+  ReplayToJsonClosure *closure = user_data;
+  g_autofree char *event_str = NULL;
+
+  if (closure->error != NULL)
+    return;
+
+  if (!closure->first)
+    {
+      if (!write_string (closure->out, ",\n  ", &closure->error))
+        return;
+    }
+
+  closure->first = FALSE;
+
+  if (strcmp (signature, "") == 0)
+    {
+      event_str = g_strdup_printf ("[%" G_GINT64_FORMAT ", \"%s\"]", time, name);
+    }
+  else if (strcmp (signature, "i") == 0)
+    {
+      event_str = g_strdup_printf ("[%" G_GINT64_FORMAT ", \"%s\", %i]",
+                                   time,
+                                   name,
+                                   g_value_get_int (arg));
+    }
+  else if (strcmp (signature, "x") == 0)
+    {
+      event_str = g_strdup_printf ("[%" G_GINT64_FORMAT ", \"%s\", %"G_GINT64_FORMAT "]",
+                                   time,
+                                   name,
+                                   g_value_get_int64 (arg));
+    }
+  else if (strcmp (signature, "s") == 0)
+    {
+      const char *arg_str = g_value_get_string (arg);
+      char *escaped = escape_quotes (arg_str);
+
+      event_str = g_strdup_printf ("[%" G_GINT64_FORMAT ", \"%s\", \"%s\"]",
+                                   time,
+                                   name,
+                                   g_value_get_string (arg));
+
+      if (escaped != arg_str)
+        g_free (escaped);
+    }
+  else
+    {
+      g_assert_not_reached ();
+    }
+
+  if (!write_string (closure->out, event_str, &closure->error))
+      return;
+}
+
+/**
+ * shell_perf_log_dump_log:
+ * @perf_log: a #ShellPerfLog
+ * @out: output stream into which to write the event log
+ * @error: location to store #GError, or %NULL
+ *
+ * Writes the performance event log, formatted as JSON, to the specified
+ * output stream. For performance reasons, the output stream passed
+ * in should generally be a buffered (or memory) output stream, since
+ * it will be written to in small pieces. The JSON output is an array
+ * with the elements of the array also being arrays, of the form
+ * '[' <time>, <event name> [, <event_arg>... ] ']'.
+ *
+ * Return value: %TRUE if the dump succeeded. %FALSE if an IO error occurred
+ */
+gboolean
+shell_perf_log_dump_log (ShellPerfLog   *perf_log,
+                         GOutputStream  *out,
+                         GError        **error)
+{
+  ReplayToJsonClosure closure;
+
+  closure.out = out;
+  closure.error = NULL;
+  closure.first = TRUE;
+
+  if (!write_string (out, "[ ", &closure.error))
+    return FALSE;
+
+  shell_perf_log_replay (perf_log, replay_to_json, &closure);
+
+  if (closure.error != NULL)
+    {
+      g_propagate_error (error, closure.error);
+      return FALSE;
+    }
+
+  if (!write_string (out, " ]", &closure.error))
+    return FALSE;
+
+  return TRUE;
+}