Suppose a function <code>G</code> defers a function <code>D</code> that calls
<code>recover</code> and a panic occurs in a function on the same goroutine in which <code>G</code>
is executing.
When the running of deferred functions reaches <code>D</code>,
the return value of <code>D</code>'s call to <code>recover</code> will be the value passed to the call of <code>panic</code>.
If <code>D</code> returns normally, without starting a new

	// is too large we are basically just thrashing the CPU D-cache.
	// So if the result length is larger than an empirically-found
	// limit (8KB), we stop growing the source string once the limit
	// is reached and keep reusing the same source string - that
	// should therefore be always resident in the L1 cache - until we
	// have completed the construction of the result.
	// This yields significant speedups (up to +100%) in cases where

Suppose a function <code>G</code> defers a function <code>D</code> that calls
<code>recover</code> and a panic occurs in a function on the same goroutine in which <code>G</code>
is executing.
When the running of deferred functions reaches <code>D</code>,
the return value of <code>D</code>'s call to <code>recover</code> will be the value passed to the call of <code>panic</code>.
If <code>D</code> returns normally, without starting a new

		spd = append(spd, sparseEntry{Offset: offset, Length: length})
		sparseMap = sparseMap[2:]
	}
	return spd, nil
}

// Read reads from the current file in the tar archive.
// It returns (0, io.EOF) when it reaches the end of that file,
// until [Next] is called to advance to the next file.
//
// If the current file is sparse, then the regions marked as a hole
// are read back as NUL-bytes.
//

//go:build unix

package tar

import (
	"io/fs"
	"os/user"
	"runtime"
	"strconv"
	"sync"
	"syscall"
)

func init() {
	sysStat = statUnix
}

// userMap and groupMap caches UID and GID lookups for performance reasons.
// The downside is that renaming uname or gname by the OS never takes effect.
var userMap, groupMap sync.Map // map[int]string