threads and thread-local storage. The runtime package declares a few
variables:

	var (
		iscgo             bool
		_cgo_init         unsafe.Pointer
		_cgo_thread_start unsafe.Pointer
	)

Any package using cgo imports "runtime/cgo", which provides
initializations for these variables. It sets iscgo to true, _cgo_init
to a gcc-compiled function that can be called early during program

Variables may also be initialized using functions named <code>init</code>
declared in the package block, with no arguments and no result parameters.
</p>

<pre>
func init() { … }
</pre>

<p>
Multiple such functions may be defined per package, even within a single
source file. In the package block, the <code>init</code> identifier can
be used only to declare <code>init</code> functions, yet the identifier

var testBytes []byte  // test data; same as testString but as a slice.

type negativeReader struct{}

func (r *negativeReader) Read([]byte) (int, error) { return -1, nil }

func init() {
	testBytes = make([]byte, N)
	for i := 0; i < N; i++ {
		testBytes[i] = 'a' + byte(i%26)
	}
	testString = string(testBytes)
}

// Verify that contents of buf match the string s.

	if len(r.File) != 5 {
		t.Errorf("Archive has unexpected number of files, got %d, want 5", len(r.File))
	}
}

func TestCVE202139293(t *testing.T) {
	// directory size is so large, that the check in Reader.init
	// overflows when subtracting from the archive size, causing
	// the pre-allocation check to be bypassed.
	data := []byte{
		0x50, 0x4b, 0x06, 0x06, 0x05, 0x06, 0x31, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50, 0x4b,

Variables may also be initialized using functions named <code>init</code>
declared in the package block, with no arguments and no result parameters.
</p>

<pre>
func init() { … }
</pre>

<p>
Multiple such functions may be defined per package, even within a single
source file. In the package block, the <code>init</code> identifier can
be used only to declare <code>init</code> functions, yet the identifier

// license that can be found in the LICENSE file.

//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.

</p>

<h2 id="synchronization">Synchronization</h2>

<h3 id="init">Initialization</h3>

<p>
Program initialization runs in a single goroutine,
but that goroutine may create other goroutines,
which run concurrently.
</p>

<p class="rule">
If a package <code>p</code> imports package <code>q</code>, the completion of
<code>q</code>'s <code>init</code> functions happens before the start of any of <code>p</code>'s.
</p>