Limitations

Developing programs on the Solana blockchain has some inherent limitation associated with them. Below is a list of common limitation that you may run into.

Rust libraries

Since Rust based onchain programs must run be deterministic while running in a resource-constrained, single-threaded environment, they have some limitations on various libraries.

On-chain Rust programs support most of Rust's libstd, libcore, and liballoc, as well as many 3rd party crates.

There are some limitations since these programs run in a resource-constrained, single-threaded environment, as well as being deterministic:

• No access to
  • rand
  • std::fs
  • std::net
  • std::future
  • std::process
  • std::sync
  • std::task
  • std::thread
  • std::time
• Limited access to:
  • std::hash
  • std::os
• Bincode is extremely computationally expensive in both cycles and call depth and should be avoided
• String formatting should be avoided since it is also computationally expensive.
• No support for println!, print!, use the msg! macro instead.
• The runtime enforces a limit on the number of instructions a program can execute during the processing of one instruction. See computation budget for more information.

Compute budget

To prevent abuse of the blockchain's computational resources, each transaction is allocated a compute budget. Exceeding this compute budget will result in the transaction failing.

See the computational constraints documentation for more specific details.

Call stack depth - CallDepthExceeded error

Solana programs are constrained to run quickly, and to facilitate this, the program's call stack is limited to a max depth of 64 frames.

When a program exceeds the allowed call stack depth limit, it will receive the CallDepthExceeded error.

CPI call depth - CallDepth error

Cross-program invocations allow programs to invoke other programs directly, but the depth is constrained currently to 4.

When a program exceeds the allowed cross-program invocation call depth, it will receive a CallDepth error

Float Rust types support

Programs support a limited subset of Rust's float operations. If a program attempts to use a float operation that is not supported, the runtime will report an unresolved symbol error.

Float operations are performed via software libraries, specifically LLVM's float built-ins. Due to the software emulated, they consume more compute units than integer operations. In general, fixed point operations are recommended where possible.

The Solana Program Library math tests will report the performance of some math operations. To run the test, sync the repo and run:

cargo test-sbf -- --nocapture --test-threads=1

Recent results show the float operations take more instructions compared to integers equivalents. Fixed point implementations may vary but will also be less than the float equivalents:

          u64   f32
Multiply    8   176
Divide      9   219

Static writable data

Program shared objects do not support writable shared data. Programs are shared between multiple parallel executions using the same shared read-only code and data. This means that developers should not include any static writable or global variables in programs. In the future a copy-on-write mechanism could be added to support writable data.

Signed division

The SBF instruction set does not support signed division.