buffer_syntax.md

Buffer Specification Syntax

Example

// First line is always the emit command.
emit C++;

// Buffer name and default buffer size.
buffer name 512;

// options go here

// Frame declarations after
frame simple {
  int a, b, c;
  double d;
  interval time duration;
  interval int seqnos;
}

frame complex {
   interval counter perfctrs;
   int array_sz;
}

Emit Line

The emit line specifies a language. Only C++ is currently supported.

Options

option time timeval;
option time timespec <realtime|realtime_course|monotonic|monotonic_course|monotonic_raw|boottime|proc_cputime|thread_cputime>;
option runtime multithread <true|false>;
option tag key value;

Time Options

For timestamps (of type time in frames), there are two primary system calls available:

• gettimeofday(2) - which works on struct timeval, microsecond precision
• clock_gettime(2) - which works on struct timespec, nanosecond precision

You specify the type of structure to use, and that determines which system call the ppt-generated code uses. clock_gettime(2) takes an additional parameter. That is specified in the last argument to the option. These correspond to the clk_id argument. Note that ppt does not check if the system used is new enough to support the given clock.

Runtime options

The only runtime option supported is multithread, which generates code that supports writing from multiple threads. The non-multithread code is faster.

Tags

Tags are user-defined arbitrary strings embedded within the generated code. ppt can print these out. Tags can be useful for storing metadata. Tag keys and values can be uoted strings. Use double quotes only.

Frame specifications

One or more frame specifications are last in the buffer specification. They specify objects that can be put in the buffer. All frames in a buffer share the same buffer, and are padded to be the same size. Frame members can be:

• int
• double
• time
• counter

Or an interval of one of these types.