一：dex 相关文件生成流程
1. PKMS.scanPackageDirtyLI
PKMS 中，进行dex 相关处理的流程入口是在PKMS.scanPackageDirtyLI() 函数中：
private PackageParser.Package scanPackageDirtyLI(PackageParser.Package pkg, int parseFlags,
int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
... ...
final boolean forceDex = (scanFlags & SCAN_FORCE_DEX) != 0;
... ...
if ((scanFlags & SCAN_NO_DEX) == 0) {
int result = mPackageDexOptimizer.performDexOpt(pkg, null /* instruction sets */,
forceDex, (scanFlags & SCAN_DEFER_DEX) != 0, false /* inclDependencies */,
(scanFlags & SCAN_BOOTING) == 0);
if (result == PackageDexOptimizer.DEX_OPT_FAILED) {
throw new PackageManagerException(INSTALL_FAILED_DEXOPT, "scanPackageLI");
}
}
... ...
}调用了PackageDexOptimizer.performDexOpt函数，这个函数又继续调用了performDexOptLI函数：
1.1 performDexOptLI
private int performDexOptLI(PackageParser.Package pkg, String[] targetInstructionSets,
boolean forceDex, boolean defer, boolean bootComplete, ArraySet<String> done) {
... ...
if (done != null) {
done.add(pkg.packageName);
if (pkg.usesLibraries != null) {
performDexOptLibsLI(pkg.usesLibraries, instructionSets, forceDex, defer,
bootComplete, done);
}
if (pkg.usesOptionalLibraries != null) {
performDexOptLibsLI(pkg.usesOptionalLibraries, instructionSets, forceDex, defer,
bootComplete, done);
}
}
... ...
}performDexOptLI 先处理 共享库dex 相关问题：调用performDexOptLibsLI 检查对应的共享库是否已经dex：
1.1.1 performDexOptLibsLI
private void performDexOptLibsLI(ArrayList<String> libs, String[] instructionSets,
boolean forceDex, boolean defer, boolean bootComplete, ArraySet<String> done) {
for (String libName : libs) {
PackageParser.Package libPkg = mPackageManagerService.findSharedNonSystemLibrary(
libName);
if (libPkg != null && !done.contains(libName)) {
performDexOptLI(libPkg, instructionSets, forceDex, defer, bootComplete, done);
}
}
}
遍历需要dex 的库组合libs中每个库对应的pkg是否已经dex，没有则先调用 performDexOptLI 来dex 之前需要dex的lib所对应的pkg。
1.2 performDexOptLI （2）
... ...
final List<String> paths = pkg.getAllCodePathsExcludingResourceOnly();
boolean performedDexOpt = false;
// There are three basic cases here:
// 1.) we need to dexopt, either because we are forced or it is needed
// 2.) we are deferring a needed dexopt
// 3.) we are skipping an unneeded dexopt
final String[] dexCodeInstructionSets = getDexCodeInstructionSets(instructionSets);
for (String dexCodeInstructionSet : dexCodeInstructionSets) {
if (!forceDex && pkg.mDexOptPerformed.contains(dexCodeInstructionSet)) {//没有强制或者已经dex优化过直接continue
continue;
}
//(1): 遍历此pkg所以普resource相关路径
for (String path : paths) {
final int dexoptNeeded;
if (forceDex) {
dexoptNeeded = DexFile.DEX2OAT_NEEDED;
} else {
try {
dexoptNeeded = DexFile.getDexOptNeeded(path, pkg.packageName,
dexCodeInstructionSet, defer);
} catch (IOException ioe) {
Slog.w(TAG, "IOException reading apk: " + path, ioe);
return DEX_OPT_FAILED;
}
}
if (!forceDex && defer && dexoptNeeded != DexFile.NO_DEXOPT_NEEDED) {
// We're deciding to defer a needed dexopt. Don't bother dexopting for other
// paths and instruction sets. We'll deal with them all together when we process
// our list of deferred dexopts.
addPackageForDeferredDexopt(pkg);
return DEX_OPT_DEFERRED;
}
if (dexoptNeeded != DexFile.NO_DEXOPT_NEEDED) {
final String dexoptType;
String oatDir = null;
if (dexoptNeeded == DexFile.DEX2OAT_NEEDED) {
dexoptType = "dex2oat";//dex-opt类型
try {
oatDir = createOatDirIfSupported(pkg, dexCodeInstructionSet);//获取otaDir
} catch (IOException ioe) {
Slog.w(TAG, "Unable to create oatDir for package: " + pkg.packageName);
return DEX_OPT_FAILED;
}
} else if (dexoptNeeded == DexFile.PATCHOAT_NEEDED) {
dexoptType = "patchoat";
} else if (dexoptNeeded == DexFile.SELF_PATCHOAT_NEEDED) {
dexoptType = "self patchoat";
} else {
throw new IllegalStateException("Invalid dexopt needed: " + dexoptNeeded);
}
Log.i(TAG, "Running dexopt (" + dexoptType + ") on: " + path + " pkg="//关键信息打印
+ pkg.applicationInfo.packageName + " isa=" + dexCodeInstructionSet
+ " vmSafeMode=" + vmSafeMode + " debuggable=" + debuggable
+ " oatDir = " + oatDir + " bootComplete=" + bootComplete);
final int sharedGid = UserHandle.getSharedAppGid(pkg.applicationInfo.uid);
final int ret = mPackageManagerService.mInstaller.dexopt(path, sharedGid,//调用installd的dexopt
!pkg.isForwardLocked(), pkg.packageName, dexCodeInstructionSet,
dexoptNeeded, vmSafeMode, debuggable, oatDir, bootComplete);
// Dex2oat might fail due to compiler / verifier errors. We soldier on
// regardless, and attempt to interpret the app as a safety net.
if (ret == 0) {//Installd dexopt成功了
performedDexOpt = true;
}
}
}
// At this point we haven't failed dexopt and we haven't deferred dexopt. We must
// either have either succeeded dexopt, or have had getDexOptNeeded tell us
// it isn't required. We therefore mark that this package doesn't need dexopt unless
// it's forced. performedDexOpt will tell us whether we performed dex-opt or skipped
// it.
pkg.mDexOptPerformed.add(dexCodeInstructionSet);//这代表已经处理过了
}
// If we've gotten here, we're sure that no error occurred and that we haven't
// deferred dex-opt. We've either dex-opted one more paths or instruction sets or
// we've skipped all of them because they are up to date. In both cases this
// package doesn't need dexopt any longer.
return performedDexOpt ? DEX_OPT_PERFORMED : DEX_OPT_SKIPPED;
遍历apk所有的代码路径，根据解析得到dexoptType，最后用installd来完成dexopt工作，其中：
dexoptType = dex2oat 时 ，调用createOatDirIfSupported 获取oatdir ，其他dexoptType 则oatdir = null ：
private String createOatDirIfSupported(PackageParser.Package pkg, String dexInstructionSet)
throws IOException {
if (!pkg.canHaveOatDir()) {
return null;
}
File codePath = new File(pkg.codePath);
if (codePath.isDirectory()) {
File oatDir = getOatDir(codePath);
mPackageManagerService.mInstaller.createOatDir(oatDir.getAbsolutePath(),
dexInstructionSet);
return oatDir.getAbsolutePath();
}
return null;
}createOatDirIfSupported函数的逻辑是 ：
1 .codePath如果是目录，就用Installd在该目录下创建一个目录，如果是apk文件直接返回空。
2.调用pkg.canHaveOatDir 来判断，pkg 是一个NOT updated 的system app。
3.Installd.dexopt
int dexopt(const char *apk_path, uid_t uid, bool is_public,
const char *pkgname, const char *instruction_set, int dexopt_needed,
bool vm_safe_mode, bool debuggable, const char* oat_dir, bool boot_complete)
{
......
// Early best-effort check whether we can fit the the path into our buffers.
// Note: the cache path will require an additional 5 bytes for ".swap", but we'll try to run
// without a swap file, if necessary.
if (strlen(apk_path) >= (PKG_PATH_MAX - 8)) {
ALOGE("apk_path too long '%s'\n", apk_path);
return -1;
}
if (oat_dir != NULL && oat_dir[0] != '!') {
if (validate_apk_path(oat_dir)) {
ALOGE("invalid oat_dir '%s'\n", oat_dir);
return -1;
}
if (calculate_oat_file_path(out_path, oat_dir, apk_path, instruction_set)) {
return -1;
}
} else {
if (create_cache_path(out_path, apk_path, instruction_set)) {
return -1;
}
}1.oat_dir为空则调用create_cache_path函数来计算out_path
2.oat_dir不为空且有效则会根据这个oat_dir调用calculate_oat_file_path计算这个out_path
3.1 calculate_oat_file_path
int calculate_oat_file_path(char path[PKG_PATH_MAX], const char *oat_dir, const char *apk_path,
const char *instruction_set) {
char *file_name_start;
char *file_name_end;
file_name_start = strrchr(apk_path, '/');
if (file_name_start == NULL) {
ALOGE("apk_path '%s' has no '/'s in it\n", apk_path);
return -1;
}
file_name_end = strrchr(apk_path, '.');
if (file_name_end < file_name_start) {
ALOGE("apk_path '%s' has no extension\n", apk_path);
return -1;
}
// Calculate file_name
int file_name_len = file_name_end - file_name_start - 1;
char file_name[file_name_len + 1];
memcpy(file_name, file_name_start + 1, file_name_len);
file_name[file_name_len] = '\0';
// <apk_parent_dir>/oat/<isa>/<file_name>.odex
snprintf(path, PKG_PATH_MAX, "%s/%s/%s.odex", oat_dir, instruction_set, file_name);
return 0;
}最终生成/sytstem/app/XXXX/arm/oat/XXXX.odex
3.2 create_cache_path
int create_cache_path(char path[PKG_PATH_MAX], const char *src, const char *instruction_set)
{
char *tmp;
int srclen;
int dstlen;
srclen = strlen(src);
/* demand that we are an absolute path */
if ((src == 0) || (src[0] != '/') || strstr(src,"..")) {
return -1;
}
if (srclen > PKG_PATH_MAX) { // XXX: PKG_NAME_MAX?
return -1;
}
dstlen = srclen + strlen(DALVIK_CACHE_PREFIX) +
strlen(instruction_set) +
strlen(DALVIK_CACHE_POSTFIX) + 2;
if (dstlen > PKG_PATH_MAX) {
return -1;
}
sprintf(path,"%s%s/%s%s",
DALVIK_CACHE_PREFIX,
instruction_set,
src + 1, /* skip the leading / */
DALVIK_CACHE_POSTFIX);
for(tmp = path + strlen(DALVIK_CACHE_PREFIX) + strlen(instruction_set) + 1; *tmp; tmp++) {
if (*tmp == '/') {
*tmp = '@';
}
}
return 0;
}其中，DALVIK_CACHE_PREFIX = “/data/dalvik-cache/” ，,最后会在DALVIK_CACHE_PREFIX目录下创建，也就是最终会在这个目录下生成dex文件。
继续分析dexopt函数，根据dexopt类型来看源文件，一般是apk文件：
switch (dexopt_needed) {
case DEXOPT_DEX2OAT_NEEDED:
input_file = apk_path;
break;
case DEXOPT_PATCHOAT_NEEDED:
if (!calculate_odex_file_path(in_odex_path, apk_path, instruction_set)) {
return -1;
}
input_file = in_odex_path;
break;
case DEXOPT_SELF_PATCHOAT_NEEDED:
input_file = out_path;
break;
default:
ALOGE("Invalid dexopt needed: %d\n", dexopt_needed);
exit(72);
}二.优化：
1.预编译提取Odex：
在BoardConfig.mk中定义：WITH_DEXPREOPT := true。打开这个宏之后，无论是有源码还是无源码的预置apk预编译时都会提取odex文件。
优点：
开启预编译后，生成的system.img 中APP 文件夹中包含已经odex 的文件，系统第一次开机时将不必进行Odex：
缺点：
1.打开WITH_DEXPREOPT 宏之后，会导致system.img 的size 变大，需要对应的调整partition.xml 才能正常烧录；
1.1 预编译时跳过一些apk的odex提取
Android.mk 中 “LOCAL_DEX_PREOPT = false ”则不进行预优化 ；
“LOCAL_DEX_PREOPT = true ” 则进行预优化