1 Toplevel Interface
2 Collecting Profile Information
3 Analyzing Profile Data
4 Profile Renderers
4.1 Textual Rendering
4.2 Graph Rendering

Profile: Statistical Profiler

The profile collection implements a statistical profiler. The profiling is done by running a background thread that collects stack snapshots via continuation-mark-set->context, meaning that the result is an estimate of the execution costs and it is limited to the kind of information that continuation-mark-set->context produces (most notably being limited to functions calls, and subject to compiler optimizations); but the result is often useful. In practice, since this method does not require recompilation of your source and has very little runtime overhead, it can be used for longer runs which compensates for these limits.

    1 Toplevel Interface

    2 Collecting Profile Information

    3 Analyzing Profile Data

    4 Profile Renderers

      4.1 Textual Rendering

      4.2 Graph Rendering

1 Toplevel Interface

 (require profile)

This module provides one procedure and one macro that are convenient high-level entry points for profiling expressions. It abstracts over details that are available through other parts of the library, and is intended as a convenient tool for profiling code.


(profile-thunk thunk    
  [#:delay delay    
  #:repeat iterations    
  #:threads threads?    
  #:render renderer    
  #:periodic-renderer periodic-renderer])  void?
  thunk : (-> any/c)
  delay : (>=/c 0.0) = 0.05
  iterations : exact-nonnegative-integer? = 1
  threads? : any/c = #f
  renderer : (profile? . -> . any/c) = text:render
  periodic-renderer : 
(or/c #f (list/c (>=/c 0.0)
                 (profile? . -> . any/c)))
   = #f
Executes the given thunk and collect profiling data during execution, eventually analyzing and rendering this. Keyword arguments can customize the profiling:
  • The profiler works by starting a “sampler” thread to periodically collect stack snapshots (using continuation-mark-set->context). To determine the frequency of these collections, the sampler thread sleeps delay seconds between collections. Note that this is will be close, but not identical to, the frequency in which data is actually sampled. (The delay value is passed on to create-sampler, which creates the sampler thread.)

  • Due to the statistical nature of the profiler, longer executions result in more accurate analysis. You can specify a number of iterations to repeat the thunk to collect more data.

  • Normally, the sampler collects only snapshots of the current-thread’s stack. Profiling a computation that creates threads will therefore lead to bad analysis: the timing results will be correct, but because the profiler is unaware of other threads the observed time will be suspiciously small, and work done in other threads will not be included in the results. To track all threads, specify a non-#f value for the threads? argument—this will execute the computation in a fresh custodian, and keep track of all threads under this custodian.

  • Once the computation is done and the sampler is stopped, the accumulated data is analyzed (by analyze-samples) and the resulting profile value is sent to the renderer function. See Profile Renderers for available renderers. You can also use values as a “renderer”—in this case profile-thunk returns the analyzed information which can now be rendered multiple times, or saved for rendering directly using one of the renderers, perhaps multiple times for different views.

  • To provide feedback information during execution, specify a periodic-renderer. This should be a list holding a delay time (in seconds) and a renderer function. The delay determines the frequency in which the renderer is called, and it should be larger than the sampler delay (usually much larger since it can involve more noticeable overhead, and it is intended for a human observer).


(profile expr keyword-arguments ...)

A macro version of profile-thunk. Keyword arguments can be specified as in a function call: they can appear before and/or after the expression to be profiled.

2 Collecting Profile Information

 (require profile/sampler)


(create-sampler to-track delay [super-cust])

  ((symbol?) (any/c) . ->* . any/c)
  to-track : 
(or/c thread? custodian?
      (listof (or/c thread? custodian?)))
  delay : (>=/c 0.0)
  super-cust : custodian? = (current-custodian)
Creates a stack-snapshot collector thread, which tracks the given to-track value every delay seconds. The to-track value can be either a thread (track just that thread), a custodian (track all threads managed by the custodian), or a list of threads and/or custodians. If a custodian is given, it must be subordinate to super-cust, which defaults to the current custodian.

The resulting value is a controller function, which consumes a message consisting of a symbol and an optional argument, and can affect the sampler. The following messages are currently supported:
  • 'pause and 'resume will stop or resume snapshot collection. These messages can be nested. Note that the thread will continue running—it will just stop collecting snapshots.

  • 'stop kills the sampler thread. It should be called when no additional data should be collected. (This is currently irreversible: there is no message to start a new sampler thread.)

  • 'set-tracked! with a value will change the tracked object(s) which were initially specified as the to-track argument.

  • 'set-tracked! with a numeric value will change the delay that the sampler is taking between snapshots. Note that although changing this means that the snapshots are not uniformly distributed, the results will still be correct: the cpu time between samples is taken into account when the collected data is analyzed.

  • Finally, a 'get-snapshots message will make the controller return the currently collected data. Note that this can be called multiple times, each call will return the data that is collected up to that point in time. In addition, it can be (and usually is) called after the sampler was stopped.

    The value that is returned should be considered as an undocumented internal detail of the profiler, intended to be sent to analyze-samples for analysis. The reason this is not done automatically, is that a future extension might allow you to combine several sampler results, making it possible to combine a profile analysis from several individual runs, possibly from different machines.

3 Analyzing Profile Data

 (require profile/analyzer)

Once a profile run is done and the results are collected, the next step is to analyze the data. In this step sample times are computed and summed, a call-graph representing observed function calls is built, and per-node and per-edge information is created. This is the job of the main function provided by profile/analyzer.


(analyze-samples raw-sample-data)  profile?

  raw-sample-data : any/c
This function consumes the raw result of the sampler (given in an undocumented form), analyzes it, and returns a profile value holding the analyzed results. Without this function, the results of the sampler should be considered meaningless.


(struct profile (total-time
  total-time : exact-nonnegative-integer?
  cpu-time : exact-nonnegative-integer?
  sample-number : exact-nonnegative-integer?
  thread-times : 
(listof (cons exact-nonnegative-integer?
  nodes : (listof node?)
  *-node : node?
Represents an analyzed profile result.


(struct node (id src thread-ids total self callers callees))

  id : (or/c #f symbol?)
  src : (or/c #f srcloc?)
  thread-ids : (listof exact-nonnegative-integer?)
  total : exact-nonnegative-integer?
  self : exact-nonnegative-integer?
  callers : (listof edge?)
  callees : (listof edge?)
Represents a function call node in the call graph of an analyzed profile result.


(struct edge (total caller caller-time callee callee-time))

  total : exact-nonnegative-integer?
  caller : node?
  caller-time : exact-nonnegative-integer?
  callee : node?
  callee-time : exact-nonnegative-integer?
Represents an edge between two function call nodes in the call graph of an analyzed profile result.

4 Profile Renderers

After collecting the profile samples and analyzing the data, the last step of the profiling process is to render the results. The profile collection provides several renderers, each providing a rendering function that consumes a profile instance. See the analyzer section for a description of the profile struct if you want to implement a new renderer.

4.1 Textual Rendering

 (require profile/render-text)


(render profile-data    
  [#:truncate-source truncate-source    
  #:hide-self hide-self%    
  #:hide-subs hide-subs%])  void?
  profile-data : profile?
  truncate-source : exact-nonnegative-integer? = 50
  hide-self% : (between/c 0 1) = 1/100
  hide-subs% : (between/c 0 1) = 1/50
Prints the given profile results as a textual table.

The printout begins with general information about the profile, followed by a table with an entry for each function in the call graph. The entries are displayed in a topological order (roughly, since the graph can have cycles). This means that it is usually easy to find the callers and callees of a function in its close environment.

Each row in the table has the following format:

                          B [M1] M2%

  [N1] N2(N3%) N4(N5%)  A ...path/to/source.rkt:12:34

                          C [M3] M4%

with the following meaning of the numbers and labels:
  • A the name of the function that this node represents, followed by the source location for the function if it is known. The name can be “???” for anonymous functions, which will be identified with their source location.

  • N1 an integer label associated with this node in the printout. This label is used to mark references to this function, since symbolic names are not unique (and they can be missing or very long). The labels are assigned from the top.

  • N2 the time (in milliseconds) that this function has been anywhere in a stack snapshot. This is the total time that the execution was somewhere in this function or in its callees. (Corresponds to the node-total field.)

  • N3 this is the percentage of the node’s total time (N2) from the total observed time of the profile. An entry with a 100% refers to a function that was active throughout the whole execution.

  • N4 the time (in milliseconds) that this function has been at the top of the stack snapshot. This is the time that this function was itself doing work rather than calling other functions. (Corresponds to the node-self field.)

  • N5 this is the percentage of N4 out of the total observed time of the profile. Functions with high values here can be good candidates for optimization, But, of course, they can represent doing real work for a caller that needs to be optimized.

  • B and C these are labels for the callers and callees of the function. Any number of callers and callees can appear here (including 0). The function itself can also appear in both places if it is (non-tail) recursive.

  • M1 and M3 the index numbers for B and C. They can be used to disambiguate functions with the same name, as well as a quick way to find the corresponding entry in the table.

  • M2 and M4 the percentages of the time A spent being called by B and calling C. These percentages represent the time that this edge was found on a stack snapshot, divided by the number of occurrences of A on the same snapshot. The number is the percentage of these times out of N2, the total time A has been active.

    The total percentages for the all caller and for all callees should be close to 100% minus the time A was the leaf or the root.

    These values correspond to the edge-caller-time and edge-callee-time fields; see the documentation for further details.

The function has a few keyword arguments to customize its output:
  • The truncate-source argument determines the length that the source string should take (together with its label).

  • hide-self% and hide-subs% control hiding some of the nodes. A node is hidden if its self time (N3 in the above example) is smaller than hide-self% and if all places where it occurs as a caller or a callee have percentages that are smaller than hide-subs%. The reason for requiring both conditions is to avoid having “dangling references” to hidden nodes.

4.2 Graph Rendering

 (require profile/render-graphviz)


(render profile-data    
  [#:hide-self hide-self%    
  #:hide-subs hide-subs%])  void?
  profile-data : profile?
  hide-self% : (between/c 0 1) = 1/100
  hide-subs% : (between/c 0 1) = 1/50
Prints the given profile results as a Graphviz directed graph.

This is an experimental module, provided mostly as a proof-of-concept. It renders the profile’s call-graph as a graph representation for one of the Graphviz tools to render. Nodes are colored according to their ‘self’ percentages, and edges.

The keyword arguments control hiding nodes in the same way as with the textual renderer.