Faasm functions can interact with the Faasm runtime and underlying host through the host interface. This lets them do things like manage state and interact with other functions.
The host interface includes:
These cover interactions with serverless functions and their ability to invoke other functions ("chaining").
| Function | Description |
|---|---|
byte* read_call_input() |
Read input data as byte array |
void write_call_output(out_data) |
Write output data for function |
int chain_call(name, args) |
Call function and return call_id |
int await_call(call_id) |
Await completion of call_id |
byte* await_call_output(call_id) |
Await completion and get output of call_id |
This section of the host interface covers management of state as outlined in the state docs.
| Function | Description |
|---|---|
byte* get_state(key, flags) |
Read input data as byte array |
byte* get_state_offset(key, off, flags) |
Write output data for function |
void set_state(key, val) |
Write output data for function |
void set_state_offset(key, val, len, off) |
Write output data for function |
void push/pull_state(key) |
Write output data for function |
void push/pull_state_offset(key, off) |
Write output data for function |
void append_state(key, val) |
Write output data for function |
void lock_state_read/write(key) |
Write output data for function |
void lock_state_global_read/write(key) |
Write output data for function |
Faasm supports WASI, but adds and customises further POSIX-like system calls to support a broader range of legacy applications and libraries (such as CPython).
This is done in part with a modified wasi-libc.
The main additions and modifications are as follows:
| Category | Function | Description |
|---|---|---|
| Dynamic linking | void *dlopen/dlsym(...) |
Standard POSIX-like dynamic linking |
| Dynamic linking | int dlclose(...) |
As above |
| Memory | void* mmap(...), int munmap(...) |
Only permits memory growth and file mapping |
| File I/O | int dup(...) |
Necessary for certain legacy applications |
Faasm supports standard filesystem syscalls, but provides a serverless-specific implementation. Because functions may be executing on different hosts, all filesystem accesses are global-read-local-write, i.e. functions can access files from any host, but writes are only made locally. This is sufficient to support legacy filesystem use-cases, while any data sharing between functions can be done through state.
As mentioned above, Faasm also supports pthreads, which also introduce a number of extra POSIX syscalls.