github.com/lzhfromustc/gofuzz@v0.0.0-20211116160056-151b3108bbd1/runtime/metrics/doc.go (about)

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  /*
     6  Package metrics provides a stable interface to access implementation-defined
     7  metrics exported by the Go runtime. This package is similar to existing functions
     8  like runtime.ReadMemStats and debug.ReadGCStats, but significantly more general.
     9  
    10  The set of metrics defined by this package may evolve as the runtime itself
    11  evolves, and also enables variation across Go implementations, whose relevant
    12  metric sets may not intersect.
    13  
    14  Interface
    15  
    16  Metrics are designated by a string key, rather than, for example, a field name in
    17  a struct. The full list of supported metrics is always available in the slice of
    18  Descriptions returned by All. Each Description also includes useful information
    19  about the metric.
    20  
    21  Thus, users of this API are encouraged to sample supported metrics defined by the
    22  slice returned by All to remain compatible across Go versions. Of course, situations
    23  arise where reading specific metrics is critical. For these cases, users are
    24  encouraged to use build tags, and although metrics may be deprecated and removed,
    25  users should consider this to be an exceptional and rare event, coinciding with a
    26  very large change in a particular Go implementation.
    27  
    28  Each metric key also has a "kind" that describes the format of the metric's value.
    29  In the interest of not breaking users of this package, the "kind" for a given metric
    30  is guaranteed not to change. If it must change, then a new metric will be introduced
    31  with a new key and a new "kind."
    32  
    33  Metric key format
    34  
    35  As mentioned earlier, metric keys are strings. Their format is simple and well-defined,
    36  designed to be both human and machine readable. It is split into two components,
    37  separated by a colon: a rooted path and a unit. The choice to include the unit in
    38  the key is motivated by compatibility: if a metric's unit changes, its semantics likely
    39  did also, and a new key should be introduced.
    40  
    41  For more details on the precise definition of the metric key's path and unit formats, see
    42  the documentation of the Name field of the Description struct.
    43  
    44  A note about floats
    45  
    46  This package supports metrics whose values have a floating-point representation. In
    47  order to improve ease-of-use, this package promises to never produce the following
    48  classes of floating-point values: NaN, infinity.
    49  
    50  Supported metrics
    51  
    52  Below is the full list of supported metrics, ordered lexicographically.
    53  
    54  	/gc/cycles/automatic:gc-cycles
    55  		Count of completed GC cycles generated by the Go runtime.
    56  
    57  	/gc/cycles/forced:gc-cycles
    58  		Count of completed GC cycles forced by the application.
    59  
    60  	/gc/cycles/total:gc-cycles
    61  		Count of all completed GC cycles.
    62  
    63  	/gc/heap/allocs-by-size:bytes
    64  		Distribution of all objects allocated by approximate size.
    65  
    66  	/gc/heap/frees-by-size:bytes
    67  		Distribution of all objects freed by approximate size.
    68  
    69  	/gc/heap/goal:bytes
    70  		Heap size target for the end of the GC cycle.
    71  
    72  	/gc/heap/objects:objects
    73  		Number of objects, live or unswept, occupying heap memory.
    74  
    75  	/gc/pauses:seconds
    76  		Distribution individual GC-related stop-the-world pause latencies.
    77  
    78  	/memory/classes/heap/free:bytes
    79  		Memory that is completely free and eligible to be returned to
    80  		the underlying system, but has not been. This metric is the
    81  		runtime's estimate of free address space that is backed by
    82  		physical memory.
    83  
    84  	/memory/classes/heap/objects:bytes
    85  		Memory occupied by live objects and dead objects that have
    86  		not yet been marked free by the garbage collector.
    87  
    88  	/memory/classes/heap/released:bytes
    89  		Memory that is completely free and has been returned to
    90  		the underlying system. This metric is the runtime's estimate of
    91  		free address space that is still mapped into the process, but
    92  		is not backed by physical memory.
    93  
    94  	/memory/classes/heap/stacks:bytes
    95  		Memory allocated from the heap that is reserved for stack
    96  		space, whether or not it is currently in-use.
    97  
    98  	/memory/classes/heap/unused:bytes
    99  		Memory that is reserved for heap objects but is not currently
   100  		used to hold heap objects.
   101  
   102  	/memory/classes/metadata/mcache/free:bytes
   103  		Memory that is reserved for runtime mcache structures, but
   104  		not in-use.
   105  
   106  	/memory/classes/metadata/mcache/inuse:bytes
   107  		Memory that is occupied by runtime mcache structures that
   108  		are currently being used.
   109  
   110  	/memory/classes/metadata/mspan/free:bytes
   111  		Memory that is reserved for runtime mspan structures, but
   112  		not in-use.
   113  
   114  	/memory/classes/metadata/mspan/inuse:bytes
   115  		Memory that is occupied by runtime mspan structures that are
   116  		currently being used.
   117  
   118  	/memory/classes/metadata/other:bytes
   119  		Memory that is reserved for or used to hold runtime
   120  		metadata.
   121  
   122  	/memory/classes/os-stacks:bytes
   123  		Stack memory allocated by the underlying operating system.
   124  
   125  	/memory/classes/other:bytes
   126  		Memory used by execution trace buffers, structures for
   127  		debugging the runtime, finalizer and profiler specials, and
   128  		more.
   129  
   130  	/memory/classes/profiling/buckets:bytes
   131  		Memory that is used by the stack trace hash map used for
   132  		profiling.
   133  
   134  	/memory/classes/total:bytes
   135  		All memory mapped by the Go runtime into the current process
   136  		as read-write. Note that this does not include memory mapped
   137  		by code called via cgo or via the syscall package.
   138  		Sum of all metrics in /memory/classes.
   139  
   140  	/sched/goroutines:goroutines
   141  		Count of live goroutines.
   142  */
   143  package metrics