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Erlang/OTP, with DTrace patches and other experiments & bugfixing. See README text below.

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README.md

The dtrace-experiment branch of Erlang/OTP

The purpose of this branch is to bring DTrace user-space probes to the Erlang virtual machine. At the moment, it is a proof of concept: unpolished, rough, and occasionally ugly. The goal: merge this code (or something philosophically similar) into Ericsson's Erlang/OTP source distribution.

History

The first implementation of DTrace probes for the Erlang virtual machine was presented at the 2008 Erlang User Conference. That work, based on the Erlang/OTP R12 release, was discontinued due to what appears to be miscommunication with the original developers.

Several users have created Erlang port drivers, linked-in drivers, or NIFs that allow Erlang code to try to activate a probe, e.g. foo_module:dtrace_probe("message goes here!").

Goals

  1. Annotate as much of the Erlang VM as is practical.
    • The initial goal is to trace file I/O operations.
  2. Support all platforms that implement DTrace: OS X, Solaris, and (I hope) FreeBSD and NetBSD.
  3. To the extent that it's practical, support SystemTap on Linux via DTrace provider compatibility.
  4. Allow Erlang code to supply annotations.

Supported platforms

The autoconf procedure is supported, I believe, for OS X/Snow Leopard and OpenSolaris/64-bit. Just add the --enable-dtrace option your command to run the configure script.

The code has been only very lightly tested on OS X. It ought to compile on a Solaris 10 or OpenSolaris machine, but no promises yet.

The autoconf stuff is ugly right now. It could use some cleaning up. For example:

  • After editing the erlang_dtrace.d file, you need to re-run the
  • top-level "configure" script in order to update erlang_dtrace.h.
  • make clean will remove erlang_dtrace.h. A build will fail unless the top-level "configure" script is re-run to re-create that file.
  • The erlang_dtrace.h file's location should probably be moved to an OTP platform-specific build dir, for example, path/to/somewhere/i386-apple-darwin10.8.0
  • There are probably some other build by-products that are also being put into the "wrong" directory, for example, erlang_dtrace.o for Solaris platforms.

Contributions

Code contributions are welcome! This is a side project for me (SLF), so things would go faster if other people are willing to pitch in. Please use the GitHub pull request mechanism or send me an email message.

To build from scratch, use this recipe. If you're an experienced Git user and wish to add my repository as a remote repository, be my guest. Just resume the recipe at command #4.

% git clone git://github.com/slfritchie/otp.git
% cd otp
% git checkout -b dtrace-experiment origin/dtrace-experiment
% env ERL_TOP=`pwd` ./otp_build autoconf
% env ERL_TOP=`pwd` ./configure --enable-dtrace + whatever args you need
% env ERL_TOP=`pwd` make

Then make install and then start an Erlang shell via /path/to/installed/bin/erl +A 8. The Erlang shell's banner should include [dtrace].

Try using this (ugly) DTrace command to watch file I/O probes in use (tested on OS X only, sorry):

dtrace -Z -n 'erlang*:::efile_drv-entry {printf("%d %d %s | %d | %s %s , %d %d %d", arg0, arg1, arg2 == NULL ? "" : copyinstr(arg2), arg3, arg4 == NULL ? "" : copyinstr(arg4), arg5 == NULL ? "" : copyinstr(arg5), arg6, arg7, arg8)} erlang*:::efile_drv-int* {printf("%d %d %d | %d", arg0, arg1, arg2, arg3);} erlang*:::efile_drv-return {printf("%d %d %s | %d | %d %d %d", arg0, arg1, arg2 == NULL ? "" : copyinstr(arg2), arg3, arg4, arg5, arg6 ) ; }'

Implementation summary

So far, most effort has been focused on the efile_drv.erl code, which implements most file I/O on behalf of the Erlang virtual machine. This driver also presents a big challenge: its use of an I/O worker pool (enabled by using the erl +A 8 flag, for example) makes it much more difficult to trace I/O activity because each of the following may be executed in a different Pthread:

  • I/O initiation (Erlang code)
  • I/O proxy process handling, e.g. read/write when file is not opened in raw mode, operations executed by the code & file server processes. (Erlang code)
  • efile_drv command setup (C code)
  • efile_drv command execution (C code)
  • efile_drv status return (C code)

TODO: keep this description up-to-date.

Example output from lib/dtrace/examples/efile_drv.d while executing file:rename("old-name", "new-name"):

efile_drv enter tag={3,84} user tag some-user-tag | RENAME (12) | args: old-name new-name , 0 0 (port #Port<0.59>)
async I/O worker tag={3,83} | RENAME (12) | efile_drv-int_entry
async I/O worker tag={3,83} | RENAME (12) | efile_drv-int_return
efile_drv return tag={3,83} user tag  | RENAME (12) | errno 2

... where the following key can help decipher the output:

  • {3,83} is the Erlang scheduler thread number (3) and operation counter number (83) assigned to this I/O operation. Together, these two numbers form a unique ID for the I/O operation.
  • 12 is the command number for the rename operation. See the definition for FILE_RENAME in the source code file efile_drv.c or the BEGIN section of the D script lib/dtrace/examples/efile_drv.d.
  • old-name and new-name are the two string arguments for the source and destination of the rename(2) system call. The two integer arguments are unused; the simple formatting code prints the arguments anyway, 0 and 0.
  • The worker pool code was called on behalf of Erlang port #Port<0.59>.
  • The system call failed with a POSIX errno value of 2: ENOENT, because the path old-name does not exist.
  • The efile_drv-int_entry and efile_drv_int_return probes are provided in case the user is interested in measuring only the latency of code executed by efile_drv asynchronous functions by I/O worker pool threads and the OS system call that they encapsulate.

So, where does the some-user-tag string come from?

At the moment, the user tag comes from code like the following:

put(dtrace_utag, "some-user-tag"),
file:rename("old-name", "new-name").

This method of tagging I/O at the Erlang level is subject to change.

Example DTrace probe specification

/**
 * Fired when a message is sent from one local process to another.
 *
 * NOTE: The 'size' parameter is in machine-dependent words and
 *       that the actual size of any binary terms in the message
 *       are not included.
 *
 * @param sender the PID (string form) of the sender
 * @param receiver the PID (string form) of the receiver
 * @param size the size of the message being delivered (words)
 * @param token_label for the sender's sequential trace token
 * @param token_previous count for the sender's sequential trace token
 * @param token_current count for the sender's sequential trace token
 */
probe message__send(char *sender, char *receiver, uint32_t size,
                    int token_label, int token_previous, int token_current);

/**
 * Fired when a message is sent from a local process to a remote process.
 *
 * NOTE: The 'size' parameter is in machine-dependent words and 
 *       that the actual size of any binary terms in the message
 *       are not included.
 *
 * @param sender the PID (string form) of the sender
 * @param node_name the Erlang node name (string form) of the receiver
 * @param receiver the PID/name (string form) of the receiver
 * @param size the size of the message being delivered (words)
 * @param token_label for the sender's sequential trace token
 * @param token_previous count for the sender's sequential trace token
 * @param token_current count for the sender's sequential trace token
 */
probe message__send__remote(char *sender, char *node_name, char *receiver,
                            uint32_t size,
                    int token_label, int token_previous, int token_current);

/**
 * Fired when a message is queued to a local process.  This probe
 * will not fire if the sender's pid == receiver's pid.
 *
 * NOTE: The 'size' parameter is in machine-dependent words and 
 *       that the actual size of any binary terms in the message
 *       are not included.
 *
 * @param receiver the PID (string form) of the receiver
 * @param size the size of the message being delivered (words)
 * @param queue_len length of the queue of the receiving process
 * @param token_label for the sender's sequential trace token
 * @param token_previous count for the sender's sequential trace token
 * @param token_current count for the sender's sequential trace token
 */
probe message__queued(char *receiver, uint32_t size, uint32_t queue_len,
                    int token_label, int token_previous, int token_current);

/**
 * Fired when a message is 'receive'd by a local process and removed
 * from its mailbox.
 *
 * NOTE: The 'size' parameter is in machine-dependent words and 
 *       that the actual size of any binary terms in the message
 *       are not included.
 *
 * @param receiver the PID (string form) of the receiver
 * @param size the size of the message being delivered (words)
 * @param queue_len length of the queue of the receiving process
 * @param token_label for the sender's sequential trace token
 * @param token_previous count for the sender's sequential trace token
 * @param token_current count for the sender's sequential trace token
 */
probe message__receive(char *receiver, uint32_t size, uint32_t queue_len,
                    int token_label, int token_previous, int token_current);

/* ... */

/* Async driver pool */

/**
 * Show the post-add length of the async driver thread pool member's queue.
 *
 * NOTE: The port name is not available: additional lock(s) must
 *       be acquired in order to get the port name safely in an SMP
 *       environment.  The same is true for the aio__pool_get probe.
 *
 * @param port the Port (string form)
 * @param new queue length
 */
probe aio_pool__add(char *, int);

/**
 * Show the post-get length of the async driver thread pool member's queue.
 *
 * @param port the Port (string form)
 * @param new queue length
 */
probe aio_pool__get(char *, int);

/* Probes for efile_drv.c */

/**
 * Entry into the efile_drv.c file I/O driver
 *
 * For a list of command numbers used by this driver, see the section
 * "Guide to probe arguments" in ../../../README.md.  That section
 * also contains explanation of the various integer and string
 * arguments that may be present when any particular probe fires.
 *
 * TODO: Adding the port string, args[10], is a pain.  Making that
 *       port string available to all the other efile_drv.c probes
 *       will be more pain.  Is the pain worth it?  If yes, then
 *       add them everywhere else and grit our teeth.  If no, then
 *       rip it out.
 *
 * @param thread-id number of the scheduler Pthread                   arg0
 * @param tag number: {thread-id, tag} uniquely names a driver operation
 * @param user-tag string                                             arg2
 * @param command number                                              arg3
 * @param string argument 1                                           arg4
 * @param string argument 2                                           arg5
 * @param integer argument 1                                          arg6
 * @param integer argument 2                                          arg7
 * @param integer argument 3                                          arg8
 * @param integer argument 4                                          arg9
 * @param port the port ID of the busy port                       args[10]
 */
probe efile_drv__entry(int, int, char *, int, char *, char *,
                       int64_t, int64_t, int64_t, int64_t, char *);

/**
 * Entry into the driver's internal work function.  Computation here
 * is performed by a async worker pool Pthread.
 *
 * @param thread-id number
 * @param tag number
 * @param command number
 */
probe efile_drv__int_entry(int, int, int);

/**
 * Return from the driver's internal work function.
 *
 * @param thread-id number
 * @param tag number
 * @param command number
 */
probe efile_drv__int_return(int, int, int);

/**
 * Return from the efile_drv.c file I/O driver
 *
 * @param thread-id number                                            arg0
 * @param tag number                                                  arg1
 * @param user-tag string                                             arg2
 * @param command number                                              arg3
 * @param Success? 1 is success, 0 is failure                         arg4
 * @param If failure, the errno of the error.                         arg5
 */
probe efile_drv__return(int, int, char *, int, int, int);

Guide to efile_drv.c probe arguments

/* Driver op code: used by efile_drv-entry      arg3 */
/*                 used by efile_drv-int_entry  arg3 */
/*                 used by efile_drv-int_return arg3 */
/*                 used by efile_drv-return     arg3 */

#define FILE_OPEN            1                 (probe arg3)
        probe arg6 = C driver dt_i1 = flags;
        probe arg4 = C driver dt_s1 = path;

#define FILE_READ            2                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;
        probe arg8 = C driver dt_i3 = size;

#define FILE_LSEEK           3                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = offset;
        probe arg8 = C driver dt_i3 = origin;

#define FILE_WRITE           4                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;
        probe arg8 = C driver dt_i3 = size;

#define FILE_FSTAT           5                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;

#define FILE_PWD             6                 (probe arg3)
        none

#define FILE_READDIR         7                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_CHDIR           8                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_FSYNC           9                 (probe arg3)
            probe arg6 = C driver dt_i1 = fd;

#define FILE_MKDIR          10                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_DELETE         11                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_RENAME         12                 (probe arg3)
        probe arg4 = C driver dt_s1 = old_name;
        probe arg5 = C driver dt_s2 = new_name;

#define FILE_RMDIR          13                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_TRUNCATE       14                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;

#define FILE_READ_FILE      15                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_WRITE_INFO     16                 (probe arg3)
        probe arg6 = C driver dt_i1 = mode;
        probe arg7 = C driver dt_i2 = uid;
        probe arg8 = C driver dt_i3 = gid;

#define FILE_LSTAT          19                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_READLINK       20                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_LINK           21                 (probe arg3)
        probe arg4 = C driver dt_s1 = existing_path;
        probe arg5 = C driver dt_s2 = new_path;

#define FILE_SYMLINK        22                 (probe arg3)
        probe arg4 = C driver dt_s1 = existing_path;
        probe arg5 = C driver dt_s2 = new_path;

#define FILE_CLOSE          23                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;

#define FILE_PWRITEV        24                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;
        probe arg8 = C driver dt_i3 = size;

#define FILE_PREADV         25                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;
        probe arg8 = C driver dt_i3 = size;

#define FILE_SETOPT         26                 (probe arg3)
        probe arg6 = C driver dt_i1 = opt_name;
        probe arg7 = C driver dt_i2 = opt_specific_value;

#define FILE_IPREAD         27                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;
        probe arg8 = C driver dt_i3 = offsets[0];
        probe arg9 = C driver dt_i4 = size;

#define FILE_ALTNAME        28                 (probe arg3)
        probe arg4 = C driver dt_s1 = path;

#define FILE_READ_LINE      29                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = flags;
        probe arg8 = C driver dt_i3 = read_offset;
        probe arg9 = C driver dt_i4 = read_ahead;

#define FILE_FDATASYNC      30                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;

#define FILE_FADVISE        31                 (probe arg3)
        probe arg6 = C driver dt_i1 = fd;
        probe arg7 = C driver dt_i2 = offset;
        probe arg8 = C driver dt_i3 = length;
        probe arg9 = C driver dt_i4 = advise_type;

Erlang/OTP

Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecom, banking, e-commerce, computer telephony and instant messaging. Erlang's runtime system has built-in support for concurrency, distribution and fault tolerance.

OTP is set of Erlang libraries and design principles providing middle-ware to develop these systems. It includes its own distributed database, applications to interface towards other languages, debugging and release handling tools.

More information can be found at erlang.org.

Building and Installing

Information on building and installing Erlang/OTP can be found in the INSTALL.md document.

Contributing to Erlang/OTP

Here are the instructions for submitting patches.

In short:

  • We prefer to receive proposed updates via email on the erlang-patches mailing list rather than through a pull request. Pull requests are not practical because we have a strict policy never to merge any untested changes to the development branch (the only exception being obviously correct changes, such as corrections of typos).

  • We merge all proposed updates to the pu (proposed updates) branch, typically within one working day.

  • At least once a day, the contents of the pu branch will be built on several platforms (Linux, Solaris, Mac OS X, Windows, and so on) and automatic test suites will be run. We will email you if any problems are found.

  • If a proposed change builds and passes the tests, it will be reviewed by one or more members of the Erlang/OTP team at Ericsson. The reviewer may suggest improvements that are needed before the change can be accepted and merged.

  • Once or twice a week, a status email called "What's cooking in Erlang/OTP" will be sent to the erlang-patches mailing list.

Copyright and License

%CopyrightBegin%

Copyright Ericsson AB 2010. All Rights Reserved.

The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/.

Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License.

%CopyrightEnd%

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